Merge branch 'bpftool-show-pid'

Andrii Nakryiko says:

====================
This patch set implements libbpf support for a second kind of special externs,
kernel symbols, in addition to existing Kconfig externs.

Right now, only untyped (const void) externs are supported, which, in
C language, allow only to take their address. In the future, with kernel BTF
getting type info about its own global and per-cpu variables, libbpf will
extend this support with BTF type info, which will allow to also directly
access variable's contents and follow its internal pointers, similarly to how
it's possible today in fentry/fexit programs.

As a first practical use of this functionality, bpftool gained ability to show
PIDs of processes that have open file descriptors for BPF map/program/link/BTF
object. It relies on iter/task_file BPF iterator program to extract this
information efficiently.

There was a bunch of bpftool refactoring (especially Makefile) necessary to
generalize bpftool's internal BPF program use. This includes generalization of
BPF skeletons support, addition of a vmlinux.h generation, extracting and
building minimal subset of bpftool for bootstrapping.

v2->v3:
- fix sec_btf_id check (Hao);

v1->v2:
- docs fixes (Quentin);
- dual GPL/BSD license for pid_inter.bpf.c (Quentin);
- NULL-init kcfg_data (Hao Luo);

rfc->v1:
- show pids, if supported by kernel, always (Alexei);
- switched iter output to binary to support showing process names;
- update man pages;
- fix few minor bugs in libbpf w.r.t. extern iteration.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
 *.d
-/_bpftool
+/bpftool-bootstrap
 /bpftool
 bpftool*.8
 bpf-helpers.*
 FEATURE-DUMP.bpftool
 feature
 libbpf
-profiler.skel.h
+/*.skel.h
+/vmlinux.h

tools/bpf/bpftool/Documentation/bpftool-btf.rst

@@ -36,6 +36,11 @@ DESCRIPTION
 		  otherwise list all BTF objects currently loaded on the
 		  system.
 
+		  Since Linux 5.8 bpftool is able to discover information about
+		  processes that hold open file descriptors (FDs) against BTF
+		  objects. On such kernels bpftool will automatically emit this
+		  information as well.
+
 	**bpftool btf dump** *BTF_SRC*
 		  Dump BTF entries from a given *BTF_SRC*.
 

tools/bpf/bpftool/Documentation/bpftool-link.rst

@@ -37,6 +37,11 @@ DESCRIPTION
 		  zero or more named attributes, some of which depend on type
 		  of link.
 
+		  Since Linux 5.8 bpftool is able to discover information about
+		  processes that hold open file descriptors (FDs) against BPF
+		  links. On such kernels bpftool will automatically emit this
+		  information as well.
+
 	**bpftool link pin** *LINK* *FILE*
 		  Pin link *LINK* as *FILE*.
 
@@ -82,6 +87,7 @@ EXAMPLES
 
     10: cgroup  prog 25
             cgroup_id 614  attach_type egress
+            pids test_progs(223)
 
 **# bpftool --json --pretty link show**
 
@@ -91,7 +97,12 @@ EXAMPLES
             "type": "cgroup",
             "prog_id": 25,
             "cgroup_id": 614,
-            "attach_type": "egress"
+            "attach_type": "egress",
+            "pids": [{
+                    "pid": 223,
+                    "comm": "test_progs"
+                }
+            ]
         }
     ]
 

tools/bpf/bpftool/Documentation/bpftool-map.rst

@@ -62,6 +62,11 @@ DESCRIPTION
 		  Output will start with map ID followed by map type and
 		  zero or more named attributes (depending on kernel version).
 
+		  Since Linux 5.8 bpftool is able to discover information about
+		  processes that hold open file descriptors (FDs) against BPF
+		  maps. On such kernels bpftool will automatically emit this
+		  information as well.
+
 	**bpftool map create** *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE*  **entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**dev** *NAME*]
 		  Create a new map with given parameters and pin it to *bpffs*
 		  as *FILE*.
@@ -181,6 +186,7 @@ EXAMPLES
 
   10: hash  name some_map  flags 0x0
         key 4B  value 8B  max_entries 2048  memlock 167936B
+        pids systemd(1)
 
 The following three commands are equivalent:
 

tools/bpf/bpftool/Documentation/bpftool-prog.rst

@@ -75,6 +75,11 @@ DESCRIPTION
 		  program run. Activation or deactivation of the feature is
 		  performed via the **kernel.bpf_stats_enabled** sysctl knob.
 
+		  Since Linux 5.8 bpftool is able to discover information about
+		  processes that hold open file descriptors (FDs) against BPF
+		  programs. On such kernels bpftool will automatically emit this
+		  information as well.
+
 	**bpftool prog dump xlated** *PROG* [{ **file** *FILE* | **opcodes** | **visual** | **linum** }]
 		  Dump eBPF instructions of the programs from the kernel. By
 		  default, eBPF will be disassembled and printed to standard
@@ -243,6 +248,7 @@ EXAMPLES
     10: xdp  name some_prog  tag 005a3d2123620c8b  gpl run_time_ns 81632 run_cnt 10
             loaded_at 2017-09-29T20:11:00+0000  uid 0
             xlated 528B  jited 370B  memlock 4096B  map_ids 10
+            pids systemd(1)
 
 **# bpftool --json --pretty prog show**
 
@@ -262,6 +268,11 @@ EXAMPLES
             "bytes_jited": 370,
             "bytes_memlock": 4096,
             "map_ids": [10
+            ],
+            "pids": [{
+                    "pid": 1,
+                    "comm": "systemd"
+                }
             ]
         }
     ]

tools/bpf/bpftool/Makefile

@@ -42,6 +42,7 @@ CFLAGS += -O2
 CFLAGS += -W -Wall -Wextra -Wno-unused-parameter -Wno-missing-field-initializers
 CFLAGS += $(filter-out -Wswitch-enum,$(EXTRA_WARNINGS))
 CFLAGS += -DPACKAGE='"bpftool"' -D__EXPORTED_HEADERS__ \
+	-I$(if $(OUTPUT),$(OUTPUT),.) \
 	-I$(srctree)/kernel/bpf/ \
 	-I$(srctree)/tools/include \
 	-I$(srctree)/tools/include/uapi \
@@ -61,9 +62,9 @@ CLANG ?= clang
 
 FEATURE_USER = .bpftool
 FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib libcap \
-	clang-bpf-global-var
+	clang-bpf-co-re
 FEATURE_DISPLAY = libbfd disassembler-four-args zlib libcap \
-	clang-bpf-global-var
+	clang-bpf-co-re
 
 check_feat := 1
 NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
@@ -116,40 +117,56 @@ CFLAGS += -DHAVE_LIBBFD_SUPPORT
 SRCS += $(BFD_SRCS)
 endif
 
+BPFTOOL_BOOTSTRAP := $(if $(OUTPUT),$(OUTPUT)bpftool-bootstrap,./bpftool-bootstrap)
+
+BOOTSTRAP_OBJS = $(addprefix $(OUTPUT),main.o common.o json_writer.o gen.o btf.o)
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
-_OBJS = $(filter-out $(OUTPUT)prog.o,$(OBJS)) $(OUTPUT)_prog.o
 
-ifeq ($(feature-clang-bpf-global-var),1)
-	__OBJS = $(OBJS)
-else
-	__OBJS = $(_OBJS)
-endif
+VMLINUX_BTF_PATHS := $(if $(O),$(O)/vmlinux)				\
+		     $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)	\
+		     ../../../vmlinux					\
+		     /sys/kernel/btf/vmlinux				\
+		     /boot/vmlinux-$(shell uname -r)
+VMLINUX_BTF := $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
 
-$(OUTPUT)_prog.o: prog.c
-	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -DBPFTOOL_WITHOUT_SKELETONS -o $@ $<
+ifneq ($(VMLINUX_BTF),)
+ifeq ($(feature-clang-bpf-co-re),1)
 
-$(OUTPUT)_bpftool: $(_OBJS) $(LIBBPF)
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(_OBJS) $(LIBS)
+BUILD_BPF_SKELS := 1
 
-skeleton/profiler.bpf.o: skeleton/profiler.bpf.c $(LIBBPF)
+$(OUTPUT)vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL_BOOTSTRAP)
+	$(QUIET_GEN)$(BPFTOOL_BOOTSTRAP) btf dump file $< format c > $@
+
+$(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF)
 	$(QUIET_CLANG)$(CLANG) \
+		-I$(if $(OUTPUT),$(OUTPUT),.) \
 		-I$(srctree)/tools/include/uapi/ \
-		-I$(LIBBPF_PATH) -I$(srctree)/tools/lib \
+		-I$(LIBBPF_PATH) \
+		-I$(srctree)/tools/lib \
 		-g -O2 -target bpf -c $< -o $@
 
-profiler.skel.h: $(OUTPUT)_bpftool skeleton/profiler.bpf.o
-	$(QUIET_GEN)$(OUTPUT)./_bpftool gen skeleton skeleton/profiler.bpf.o > $@
+$(OUTPUT)%.skel.h: $(OUTPUT)%.bpf.o $(BPFTOOL_BOOTSTRAP)
+	$(QUIET_GEN)$(BPFTOOL_BOOTSTRAP) gen skeleton $< > $@
 
-$(OUTPUT)prog.o: prog.c profiler.skel.h
-	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<
+$(OUTPUT)prog.o: $(OUTPUT)profiler.skel.h
+
+$(OUTPUT)pids.o: $(OUTPUT)pid_iter.skel.h
+
+endif
+endif
+
+CFLAGS += $(if BUILD_BPF_SKELS,,-DBPFTOOL_WITHOUT_SKELETONS)
 
 $(OUTPUT)disasm.o: $(srctree)/kernel/bpf/disasm.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<
 
 $(OUTPUT)feature.o: | zdep
 
-$(OUTPUT)bpftool: $(__OBJS) $(LIBBPF)
-	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(__OBJS) $(LIBS)
+$(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(BOOTSTRAP_OBJS) $(LIBS)
+
+$(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
+	$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
 
 $(OUTPUT)%.o: %.c
 	$(QUIET_CC)$(CC) $(CFLAGS) -c -MMD -o $@ $<
@@ -157,7 +174,7 @@ $(OUTPUT)%.o: %.c
 clean: $(LIBBPF)-clean
 	$(call QUIET_CLEAN, bpftool)
 	$(Q)$(RM) -- $(OUTPUT)bpftool $(OUTPUT)*.o $(OUTPUT)*.d
-	$(Q)$(RM) -- $(OUTPUT)_bpftool profiler.skel.h skeleton/profiler.bpf.o
+	$(Q)$(RM) -- $(BPFTOOL_BOOTSTRAP) $(OUTPUT)*.skel.h $(OUTPUT)vmlinux.h
 	$(Q)$(RM) -r -- $(OUTPUT)libbpf/
 	$(call QUIET_CLEAN, core-gen)
 	$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.bpftool
@@ -192,6 +209,7 @@ FORCE:
 zdep:
 	@if [ "$(feature-zlib)" != "1" ]; then echo "No zlib found"; exit 1 ; fi
 
+.SECONDARY:
 .PHONY: all FORCE clean install uninstall zdep
 .PHONY: doc doc-clean doc-install doc-uninstall
 .DEFAULT_GOAL := all

tools/bpf/bpftool/btf.c

@@ -809,6 +809,7 @@ show_btf_plain(struct bpf_btf_info *info, int fd,
 			printf("%s%u", n++ == 0 ? "  map_ids " : ",",
 			       obj->obj_id);
 	}
+	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 }
@@ -841,6 +842,9 @@ show_btf_json(struct bpf_btf_info *info, int fd,
 			jsonw_uint(json_wtr, obj->obj_id);
 	}
 	jsonw_end_array(json_wtr);	/* map_ids */
+
+	emit_obj_refs_json(&refs_table, info->id, json_wtr); /* pids */
+
 	jsonw_end_object(json_wtr);	/* btf object */
 }
 
@@ -893,6 +897,7 @@ static int do_show(int argc, char **argv)
 			close(fd);
 		return err;
 	}
+	build_obj_refs_table(&refs_table, BPF_OBJ_BTF);
 
 	if (fd >= 0) {
 		err = show_btf(fd, &btf_prog_table, &btf_map_table);
@@ -939,6 +944,7 @@ static int do_show(int argc, char **argv)
 exit_free:
 	delete_btf_table(&btf_prog_table);
 	delete_btf_table(&btf_map_table);
+	delete_obj_refs_table(&refs_table);
 
 	return err;
 }

tools/bpf/bpftool/common.c

@@ -581,3 +581,311 @@ print_all_levels(__maybe_unused enum libbpf_print_level level,
 {
 	return vfprintf(stderr, format, args);
 }
+
+static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
+{
+	unsigned int id = 0;
+	int fd, nb_fds = 0;
+	void *tmp;
+	int err;
+
+	while (true) {
+		struct bpf_prog_info info = {};
+		__u32 len = sizeof(info);
+
+		err = bpf_prog_get_next_id(id, &id);
+		if (err) {
+			if (errno != ENOENT) {
+				p_err("%s", strerror(errno));
+				goto err_close_fds;
+			}
+			return nb_fds;
+		}
+
+		fd = bpf_prog_get_fd_by_id(id);
+		if (fd < 0) {
+			p_err("can't get prog by id (%u): %s",
+			      id, strerror(errno));
+			goto err_close_fds;
+		}
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			p_err("can't get prog info (%u): %s",
+			      id, strerror(errno));
+			goto err_close_fd;
+		}
+
+		if ((tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) ||
+		    (!tag && strncmp(nametag, info.name, BPF_OBJ_NAME_LEN))) {
+			close(fd);
+			continue;
+		}
+
+		if (nb_fds > 0) {
+			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
+			if (!tmp) {
+				p_err("failed to realloc");
+				goto err_close_fd;
+			}
+			*fds = tmp;
+		}
+		(*fds)[nb_fds++] = fd;
+	}
+
+err_close_fd:
+	close(fd);
+err_close_fds:
+	while (--nb_fds >= 0)
+		close((*fds)[nb_fds]);
+	return -1;
+}
+
+int prog_parse_fds(int *argc, char ***argv, int **fds)
+{
+	if (is_prefix(**argv, "id")) {
+		unsigned int id;
+		char *endptr;
+
+		NEXT_ARGP();
+
+		id = strtoul(**argv, &endptr, 0);
+		if (*endptr) {
+			p_err("can't parse %s as ID", **argv);
+			return -1;
+		}
+		NEXT_ARGP();
+
+		(*fds)[0] = bpf_prog_get_fd_by_id(id);
+		if ((*fds)[0] < 0) {
+			p_err("get by id (%u): %s", id, strerror(errno));
+			return -1;
+		}
+		return 1;
+	} else if (is_prefix(**argv, "tag")) {
+		unsigned char tag[BPF_TAG_SIZE];
+
+		NEXT_ARGP();
+
+		if (sscanf(**argv, BPF_TAG_FMT, tag, tag + 1, tag + 2,
+			   tag + 3, tag + 4, tag + 5, tag + 6, tag + 7)
+		    != BPF_TAG_SIZE) {
+			p_err("can't parse tag");
+			return -1;
+		}
+		NEXT_ARGP();
+
+		return prog_fd_by_nametag(tag, fds, true);
+	} else if (is_prefix(**argv, "name")) {
+		char *name;
+
+		NEXT_ARGP();
+
+		name = **argv;
+		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
+			p_err("can't parse name");
+			return -1;
+		}
+		NEXT_ARGP();
+
+		return prog_fd_by_nametag(name, fds, false);
+	} else if (is_prefix(**argv, "pinned")) {
+		char *path;
+
+		NEXT_ARGP();
+
+		path = **argv;
+		NEXT_ARGP();
+
+		(*fds)[0] = open_obj_pinned_any(path, BPF_OBJ_PROG);
+		if ((*fds)[0] < 0)
+			return -1;
+		return 1;
+	}
+
+	p_err("expected 'id', 'tag', 'name' or 'pinned', got: '%s'?", **argv);
+	return -1;
+}
+
+int prog_parse_fd(int *argc, char ***argv)
+{
+	int *fds = NULL;
+	int nb_fds, fd;
+
+	fds = malloc(sizeof(int));
+	if (!fds) {
+		p_err("mem alloc failed");
+		return -1;
+	}
+	nb_fds = prog_parse_fds(argc, argv, &fds);
+	if (nb_fds != 1) {
+		if (nb_fds > 1) {
+			p_err("several programs match this handle");
+			while (nb_fds--)
+				close(fds[nb_fds]);
+		}
+		fd = -1;
+		goto exit_free;
+	}
+
+	fd = fds[0];
+exit_free:
+	free(fds);
+	return fd;
+}
+
+static int map_fd_by_name(char *name, int **fds)
+{
+	unsigned int id = 0;
+	int fd, nb_fds = 0;
+	void *tmp;
+	int err;
+
+	while (true) {
+		struct bpf_map_info info = {};
+		__u32 len = sizeof(info);
+
+		err = bpf_map_get_next_id(id, &id);
+		if (err) {
+			if (errno != ENOENT) {
+				p_err("%s", strerror(errno));
+				goto err_close_fds;
+			}
+			return nb_fds;
+		}
+
+		fd = bpf_map_get_fd_by_id(id);
+		if (fd < 0) {
+			p_err("can't get map by id (%u): %s",
+			      id, strerror(errno));
+			goto err_close_fds;
+		}
+
+		err = bpf_obj_get_info_by_fd(fd, &info, &len);
+		if (err) {
+			p_err("can't get map info (%u): %s",
+			      id, strerror(errno));
+			goto err_close_fd;
+		}
+
+		if (strncmp(name, info.name, BPF_OBJ_NAME_LEN)) {
+			close(fd);
+			continue;
+		}
+
+		if (nb_fds > 0) {
+			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
+			if (!tmp) {
+				p_err("failed to realloc");
+				goto err_close_fd;
+			}
+			*fds = tmp;
+		}
+		(*fds)[nb_fds++] = fd;
+	}
+
+err_close_fd:
+	close(fd);
+err_close_fds:
+	while (--nb_fds >= 0)
+		close((*fds)[nb_fds]);
+	return -1;
+}
+
+int map_parse_fds(int *argc, char ***argv, int **fds)
+{
+	if (is_prefix(**argv, "id")) {
+		unsigned int id;
+		char *endptr;
+
+		NEXT_ARGP();
+
+		id = strtoul(**argv, &endptr, 0);
+		if (*endptr) {
+			p_err("can't parse %s as ID", **argv);
+			return -1;
+		}
+		NEXT_ARGP();
+
+		(*fds)[0] = bpf_map_get_fd_by_id(id);
+		if ((*fds)[0] < 0) {
+			p_err("get map by id (%u): %s", id, strerror(errno));
+			return -1;
+		}
+		return 1;
+	} else if (is_prefix(**argv, "name")) {
+		char *name;
+
+		NEXT_ARGP();
+
+		name = **argv;
+		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
+			p_err("can't parse name");
+			return -1;
+		}
+		NEXT_ARGP();
+
+		return map_fd_by_name(name, fds);
+	} else if (is_prefix(**argv, "pinned")) {
+		char *path;
+
+		NEXT_ARGP();
+
+		path = **argv;
+		NEXT_ARGP();
+
+		(*fds)[0] = open_obj_pinned_any(path, BPF_OBJ_MAP);
+		if ((*fds)[0] < 0)
+			return -1;
+		return 1;
+	}
+
+	p_err("expected 'id', 'name' or 'pinned', got: '%s'?", **argv);
+	return -1;
+}
+
+int map_parse_fd(int *argc, char ***argv)
+{
+	int *fds = NULL;
+	int nb_fds, fd;
+
+	fds = malloc(sizeof(int));
+	if (!fds) {
+		p_err("mem alloc failed");
+		return -1;
+	}
+	nb_fds = map_parse_fds(argc, argv, &fds);
+	if (nb_fds != 1) {
+		if (nb_fds > 1) {
+			p_err("several maps match this handle");
+			while (nb_fds--)
+				close(fds[nb_fds]);
+		}
+		fd = -1;
+		goto exit_free;
+	}
+
+	fd = fds[0];
+exit_free:
+	free(fds);
+	return fd;
+}
+
+int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len)
+{
+	int err;
+	int fd;
+
+	fd = map_parse_fd(argc, argv);
+	if (fd < 0)
+		return -1;
+
+	err = bpf_obj_get_info_by_fd(fd, info, info_len);
+	if (err) {
+		p_err("can't get map info: %s", strerror(errno));
+		close(fd);
+		return err;
+	}
+
+	return fd;
+}

tools/bpf/bpftool/link.c

@@ -143,6 +143,9 @@ static int show_link_close_json(int fd, struct bpf_link_info *info)
 		}
 		jsonw_end_array(json_wtr);
 	}
+
+	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+
 	jsonw_end_object(json_wtr);
 
 	return 0;
@@ -212,6 +215,7 @@ static int show_link_close_plain(int fd, struct bpf_link_info *info)
 				printf("\n\tpinned %s", obj->path);
 		}
 	}
+	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
 
@@ -257,6 +261,7 @@ static int do_show(int argc, char **argv)
 
 	if (show_pinned)
 		build_pinned_obj_table(&link_table, BPF_OBJ_LINK);
+	build_obj_refs_table(&refs_table, BPF_OBJ_LINK);
 
 	if (argc == 2) {
 		fd = link_parse_fd(&argc, &argv);
@@ -296,6 +301,8 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
+	delete_obj_refs_table(&refs_table);
+
 	return errno == ENOENT ? 0 : -1;
 }
 

tools/bpf/bpftool/main.c

@@ -31,6 +31,7 @@ bool relaxed_maps;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
 struct pinned_obj_table link_table;
+struct obj_refs_table refs_table;
 
 static void __noreturn clean_and_exit(int i)
 {
@@ -92,9 +93,16 @@ int cmd_select(const struct cmd *cmds, int argc, char **argv,
 	if (argc < 1 && cmds[0].func)
 		return cmds[0].func(argc, argv);
 
-	for (i = 0; cmds[i].func; i++)
-		if (is_prefix(*argv, cmds[i].cmd))
+	for (i = 0; cmds[i].cmd; i++) {
+		if (is_prefix(*argv, cmds[i].cmd)) {
+			if (!cmds[i].func) {
+				p_err("command '%s' is not supported in bootstrap mode",
+				      cmds[i].cmd);
+				return -1;
+			}
 			return cmds[i].func(argc - 1, argv + 1);
+		}
+	}
 
 	help(argc - 1, argv + 1);
 

tools/bpf/bpftool/main.h

@@ -127,11 +127,13 @@ static const char * const attach_type_name[__MAX_BPF_ATTACH_TYPE] = {
 extern const char * const map_type_name[];
 extern const size_t map_type_name_size;
 
+/* keep in sync with the definition in skeleton/pid_iter.bpf.c */
 enum bpf_obj_type {
 	BPF_OBJ_UNKNOWN,
 	BPF_OBJ_PROG,
 	BPF_OBJ_MAP,
 	BPF_OBJ_LINK,
+	BPF_OBJ_BTF,
 };
 
 extern const char *bin_name;
@@ -139,12 +141,14 @@ extern const char *bin_name;
 extern json_writer_t *json_wtr;
 extern bool json_output;
 extern bool show_pinned;
+extern bool show_pids;
 extern bool block_mount;
 extern bool verifier_logs;
 extern bool relaxed_maps;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;
 extern struct pinned_obj_table link_table;
+extern struct obj_refs_table refs_table;
 
 void __printf(1, 2) p_err(const char *fmt, ...);
 void __printf(1, 2) p_info(const char *fmt, ...);
@@ -168,12 +172,35 @@ struct pinned_obj {
 	struct hlist_node hash;
 };
 
+struct obj_refs_table {
+	DECLARE_HASHTABLE(table, 16);
+};
+
+struct obj_ref {
+	int pid;
+	char comm[16];
+};
+
+struct obj_refs {
+	struct hlist_node node;
+	__u32 id;
+	int ref_cnt;
+	struct obj_ref *refs;
+};
+
 struct btf;
 struct bpf_line_info;
 
 int build_pinned_obj_table(struct pinned_obj_table *table,
 			   enum bpf_obj_type type);
 void delete_pinned_obj_table(struct pinned_obj_table *tab);
+__weak int build_obj_refs_table(struct obj_refs_table *table,
+				enum bpf_obj_type type);
+__weak void delete_obj_refs_table(struct obj_refs_table *table);
+__weak void emit_obj_refs_json(struct obj_refs_table *table, __u32 id,
+			       json_writer_t *json_wtr);
+__weak void emit_obj_refs_plain(struct obj_refs_table *table, __u32 id,
+				const char *prefix);
 void print_dev_plain(__u32 ifindex, __u64 ns_dev, __u64 ns_inode);
 void print_dev_json(__u32 ifindex, __u64 ns_dev, __u64 ns_inode);
 
@@ -194,23 +221,28 @@ int mount_bpffs_for_pin(const char *name);
 int do_pin_any(int argc, char **argv, int (*get_fd_by_id)(int *, char ***));
 int do_pin_fd(int fd, const char *name);
 
-int do_prog(int argc, char **arg);
-int do_map(int argc, char **arg);
-int do_link(int argc, char **arg);
-int do_event_pipe(int argc, char **argv);
-int do_cgroup(int argc, char **arg);
-int do_perf(int argc, char **arg);
-int do_net(int argc, char **arg);
-int do_tracelog(int argc, char **arg);
-int do_feature(int argc, char **argv);
-int do_btf(int argc, char **argv);
+/* commands available in bootstrap mode */
 int do_gen(int argc, char **argv);
-int do_struct_ops(int argc, char **argv);
-int do_iter(int argc, char **argv);
+int do_btf(int argc, char **argv);
+
+/* non-bootstrap only commands */
+int do_prog(int argc, char **arg) __weak;
+int do_map(int argc, char **arg) __weak;
+int do_link(int argc, char **arg) __weak;
+int do_event_pipe(int argc, char **argv) __weak;
+int do_cgroup(int argc, char **arg) __weak;
+int do_perf(int argc, char **arg) __weak;
+int do_net(int argc, char **arg) __weak;
+int do_tracelog(int argc, char **arg) __weak;
+int do_feature(int argc, char **argv) __weak;
+int do_struct_ops(int argc, char **argv) __weak;
+int do_iter(int argc, char **argv) __weak;
 
 int parse_u32_arg(int *argc, char ***argv, __u32 *val, const char *what);
 int prog_parse_fd(int *argc, char ***argv);
+int prog_parse_fds(int *argc, char ***argv, int **fds);
 int map_parse_fd(int *argc, char ***argv);
+int map_parse_fds(int *argc, char ***argv, int **fds);
 int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len);
 
 struct bpf_prog_linfo;

tools/bpf/bpftool/map.c

@@ -92,162 +92,6 @@ static void *alloc_value(struct bpf_map_info *info)
 		return malloc(info->value_size);
 }
 
-static int map_fd_by_name(char *name, int **fds)
-{
-	unsigned int id = 0;
-	int fd, nb_fds = 0;
-	void *tmp;
-	int err;
-
-	while (true) {
-		struct bpf_map_info info = {};
-		__u32 len = sizeof(info);
-
-		err = bpf_map_get_next_id(id, &id);
-		if (err) {
-			if (errno != ENOENT) {
-				p_err("%s", strerror(errno));
-				goto err_close_fds;
-			}
-			return nb_fds;
-		}
-
-		fd = bpf_map_get_fd_by_id(id);
-		if (fd < 0) {
-			p_err("can't get map by id (%u): %s",
-			      id, strerror(errno));
-			goto err_close_fds;
-		}
-
-		err = bpf_obj_get_info_by_fd(fd, &info, &len);
-		if (err) {
-			p_err("can't get map info (%u): %s",
-			      id, strerror(errno));
-			goto err_close_fd;
-		}
-
-		if (strncmp(name, info.name, BPF_OBJ_NAME_LEN)) {
-			close(fd);
-			continue;
-		}
-
-		if (nb_fds > 0) {
-			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
-			if (!tmp) {
-				p_err("failed to realloc");
-				goto err_close_fd;
-			}
-			*fds = tmp;
-		}
-		(*fds)[nb_fds++] = fd;
-	}
-
-err_close_fd:
-	close(fd);
-err_close_fds:
-	while (--nb_fds >= 0)
-		close((*fds)[nb_fds]);
-	return -1;
-}
-
-static int map_parse_fds(int *argc, char ***argv, int **fds)
-{
-	if (is_prefix(**argv, "id")) {
-		unsigned int id;
-		char *endptr;
-
-		NEXT_ARGP();
-
-		id = strtoul(**argv, &endptr, 0);
-		if (*endptr) {
-			p_err("can't parse %s as ID", **argv);
-			return -1;
-		}
-		NEXT_ARGP();
-
-		(*fds)[0] = bpf_map_get_fd_by_id(id);
-		if ((*fds)[0] < 0) {
-			p_err("get map by id (%u): %s", id, strerror(errno));
-			return -1;
-		}
-		return 1;
-	} else if (is_prefix(**argv, "name")) {
-		char *name;
-
-		NEXT_ARGP();
-
-		name = **argv;
-		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
-			p_err("can't parse name");
-			return -1;
-		}
-		NEXT_ARGP();
-
-		return map_fd_by_name(name, fds);
-	} else if (is_prefix(**argv, "pinned")) {
-		char *path;
-
-		NEXT_ARGP();
-
-		path = **argv;
-		NEXT_ARGP();
-
-		(*fds)[0] = open_obj_pinned_any(path, BPF_OBJ_MAP);
-		if ((*fds)[0] < 0)
-			return -1;
-		return 1;
-	}
-
-	p_err("expected 'id', 'name' or 'pinned', got: '%s'?", **argv);
-	return -1;
-}
-
-int map_parse_fd(int *argc, char ***argv)
-{
-	int *fds = NULL;
-	int nb_fds, fd;
-
-	fds = malloc(sizeof(int));
-	if (!fds) {
-		p_err("mem alloc failed");
-		return -1;
-	}
-	nb_fds = map_parse_fds(argc, argv, &fds);
-	if (nb_fds != 1) {
-		if (nb_fds > 1) {
-			p_err("several maps match this handle");
-			while (nb_fds--)
-				close(fds[nb_fds]);
-		}
-		fd = -1;
-		goto exit_free;
-	}
-
-	fd = fds[0];
-exit_free:
-	free(fds);
-	return fd;
-}
-
-int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len)
-{
-	int err;
-	int fd;
-
-	fd = map_parse_fd(argc, argv);
-	if (fd < 0)
-		return -1;
-
-	err = bpf_obj_get_info_by_fd(fd, info, info_len);
-	if (err) {
-		p_err("can't get map info: %s", strerror(errno));
-		close(fd);
-		return err;
-	}
-
-	return fd;
-}
-
 static int do_dump_btf(const struct btf_dumper *d,
 		       struct bpf_map_info *map_info, void *key,
 		       void *value)
@@ -665,6 +509,8 @@ static int show_map_close_json(int fd, struct bpf_map_info *info)
 		jsonw_end_array(json_wtr);
 	}
 
+	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+
 	jsonw_end_object(json_wtr);
 
 	return 0;
@@ -752,6 +598,8 @@ static int show_map_close_plain(int fd, struct bpf_map_info *info)
 	if (frozen)
 		printf("%sfrozen", info->btf_id ? "  " : "");
 
+	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+
 	printf("\n");
 	return 0;
 }
@@ -810,6 +658,7 @@ static int do_show(int argc, char **argv)
 
 	if (show_pinned)
 		build_pinned_obj_table(&map_table, BPF_OBJ_MAP);
+	build_obj_refs_table(&refs_table, BPF_OBJ_MAP);
 
 	if (argc == 2)
 		return do_show_subset(argc, argv);
@@ -853,6 +702,8 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
+	delete_obj_refs_table(&refs_table);
+
 	return errno == ENOENT ? 0 : -1;
 }
 

tools/bpf/bpftool/pids.c

+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/* Copyright (C) 2020 Facebook */
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <bpf/bpf.h>
+
+#include "main.h"
+#include "skeleton/pid_iter.h"
+
+#ifdef BPFTOOL_WITHOUT_SKELETONS
+
+int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
+{
+	p_err("bpftool built without PID iterator support");
+	return -ENOTSUP;
+}
+void delete_obj_refs_table(struct obj_refs_table *table) {}
+
+#else /* BPFTOOL_WITHOUT_SKELETONS */
+
+#include "pid_iter.skel.h"
+
+static void add_ref(struct obj_refs_table *table, struct pid_iter_entry *e)
+{
+	struct obj_refs *refs;
+	struct obj_ref *ref;
+	void *tmp;
+	int i;
+
+	hash_for_each_possible(table->table, refs, node, e->id) {
+		if (refs->id != e->id)
+			continue;
+
+		for (i = 0; i < refs->ref_cnt; i++) {
+			if (refs->refs[i].pid == e->pid)
+				return;
+		}
+
+		tmp = realloc(refs->refs, (refs->ref_cnt + 1) * sizeof(*ref));
+		if (!tmp) {
+			p_err("failed to re-alloc memory for ID %u, PID %d, COMM %s...",
+			      e->id, e->pid, e->comm);
+			return;
+		}
+		refs->refs = tmp;
+		ref = &refs->refs[refs->ref_cnt];
+		ref->pid = e->pid;
+		memcpy(ref->comm, e->comm, sizeof(ref->comm));
+		refs->ref_cnt++;
+
+		return;
+	}
+
+	/* new ref */
+	refs = calloc(1, sizeof(*refs));
+	if (!refs) {
+		p_err("failed to alloc memory for ID %u, PID %d, COMM %s...",
+		      e->id, e->pid, e->comm);
+		return;
+	}
+
+	refs->id = e->id;
+	refs->refs = malloc(sizeof(*refs->refs));
+	if (!refs->refs) {
+		free(refs);
+		p_err("failed to alloc memory for ID %u, PID %d, COMM %s...",
+		      e->id, e->pid, e->comm);
+		return;
+	}
+	ref = &refs->refs[0];
+	ref->pid = e->pid;
+	memcpy(ref->comm, e->comm, sizeof(ref->comm));
+	refs->ref_cnt = 1;
+	hash_add(table->table, &refs->node, e->id);
+}
+
+static int __printf(2, 0)
+libbpf_print_none(__maybe_unused enum libbpf_print_level level,
+		  __maybe_unused const char *format,
+		  __maybe_unused va_list args)
+{
+	return 0;
+}
+
+int build_obj_refs_table(struct obj_refs_table *table, enum bpf_obj_type type)
+{
+	char buf[4096];
+	struct pid_iter_bpf *skel;
+	struct pid_iter_entry *e;
+	int err, ret, fd = -1, i;
+	libbpf_print_fn_t default_print;
+
+	hash_init(table->table);
+	set_max_rlimit();
+
+	skel = pid_iter_bpf__open();
+	if (!skel) {
+		p_err("failed to open PID iterator skeleton");
+		return -1;
+	}
+
+	skel->rodata->obj_type = type;
+
+	/* we don't want output polluted with libbpf errors if bpf_iter is not
+	 * supported
+	 */
+	default_print = libbpf_set_print(libbpf_print_none);
+	err = pid_iter_bpf__load(skel);
+	libbpf_set_print(default_print);
+	if (err) {
+		/* too bad, kernel doesn't support BPF iterators yet */
+		err = 0;
+		goto out;
+	}
+	err = pid_iter_bpf__attach(skel);
+	if (err) {
+		/* if we loaded above successfully, attach has to succeed */
+		p_err("failed to attach PID iterator: %d", err);
+		goto out;
+	}
+
+	fd = bpf_iter_create(bpf_link__fd(skel->links.iter));
+	if (fd < 0) {
+		err = -errno;
+		p_err("failed to create PID iterator session: %d", err);
+		goto out;
+	}
+
+	while (true) {
+		ret = read(fd, buf, sizeof(buf));
+		if (ret < 0) {
+			err = -errno;
+			p_err("failed to read PID iterator output: %d", err);
+			goto out;
+		}
+		if (ret == 0)
+			break;
+		if (ret % sizeof(*e)) {
+			err = -EINVAL;
+			p_err("invalid PID iterator output format");
+			goto out;
+		}
+		ret /= sizeof(*e);
+
+		e = (void *)buf;
+		for (i = 0; i < ret; i++, e++) {
+			add_ref(table, e);
+		}
+	}
+	err = 0;
+out:
+	if (fd >= 0)
+		close(fd);
+	pid_iter_bpf__destroy(skel);
+	return err;
+}
+
+void delete_obj_refs_table(struct obj_refs_table *table)
+{
+	struct obj_refs *refs;
+	struct hlist_node *tmp;
+	unsigned int bkt;
+
+	hash_for_each_safe(table->table, bkt, tmp, refs, node) {
+		hash_del(&refs->node);
+		free(refs->refs);
+		free(refs);
+	}
+}
+
+void emit_obj_refs_json(struct obj_refs_table *table, __u32 id, json_writer_t *json_wtr)
+{
+	struct obj_refs *refs;
+	struct obj_ref *ref;
+	int i;
+
+	if (hash_empty(table->table))
+		return;
+
+	hash_for_each_possible(table->table, refs, node, id) {
+		if (refs->id != id)
+			continue;
+		if (refs->ref_cnt == 0)
+			break;
+
+		jsonw_name(json_wtr, "pids");
+		jsonw_start_array(json_wtr);
+		for (i = 0; i < refs->ref_cnt; i++) {
+			ref = &refs->refs[i];
+			jsonw_start_object(json_wtr);
+			jsonw_int_field(json_wtr, "pid", ref->pid);
+			jsonw_string_field(json_wtr, "comm", ref->comm);
+			jsonw_end_object(json_wtr);
+		}
+		jsonw_end_array(json_wtr);
+		break;
+	}
+}
+
+void emit_obj_refs_plain(struct obj_refs_table *table, __u32 id, const char *prefix)
+{
+	struct obj_refs *refs;
+	struct obj_ref *ref;
+	int i;
+
+	if (hash_empty(table->table))
+		return;
+
+	hash_for_each_possible(table->table, refs, node, id) {
+		if (refs->id != id)
+			continue;
+		if (refs->ref_cnt == 0)
+			break;
+
+		printf("%s", prefix);
+		for (i = 0; i < refs->ref_cnt; i++) {
+			ref = &refs->refs[i];
+			printf("%s%s(%d)", i == 0 ? "" : ", ", ref->comm, ref->pid);
+		}
+		break;
+	}
+}
+
+
+#endif

tools/bpf/bpftool/prog.c

@@ -86,158 +86,6 @@ static void print_boot_time(__u64 nsecs, char *buf, unsigned int size)
 		strftime(buf, size, "%FT%T%z", &load_tm);
 }
 
-static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
-{
-	unsigned int id = 0;
-	int fd, nb_fds = 0;
-	void *tmp;
-	int err;
-
-	while (true) {
-		struct bpf_prog_info info = {};
-		__u32 len = sizeof(info);
-
-		err = bpf_prog_get_next_id(id, &id);
-		if (err) {
-			if (errno != ENOENT) {
-				p_err("%s", strerror(errno));
-				goto err_close_fds;
-			}
-			return nb_fds;
-		}
-
-		fd = bpf_prog_get_fd_by_id(id);
-		if (fd < 0) {
-			p_err("can't get prog by id (%u): %s",
-			      id, strerror(errno));
-			goto err_close_fds;
-		}
-
-		err = bpf_obj_get_info_by_fd(fd, &info, &len);
-		if (err) {
-			p_err("can't get prog info (%u): %s",
-			      id, strerror(errno));
-			goto err_close_fd;
-		}
-
-		if ((tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) ||
-		    (!tag && strncmp(nametag, info.name, BPF_OBJ_NAME_LEN))) {
-			close(fd);
-			continue;
-		}
-
-		if (nb_fds > 0) {
-			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
-			if (!tmp) {
-				p_err("failed to realloc");
-				goto err_close_fd;
-			}
-			*fds = tmp;
-		}
-		(*fds)[nb_fds++] = fd;
-	}
-
-err_close_fd:
-	close(fd);
-err_close_fds:
-	while (--nb_fds >= 0)
-		close((*fds)[nb_fds]);
-	return -1;
-}
-
-static int prog_parse_fds(int *argc, char ***argv, int **fds)
-{
-	if (is_prefix(**argv, "id")) {
-		unsigned int id;
-		char *endptr;
-
-		NEXT_ARGP();
-
-		id = strtoul(**argv, &endptr, 0);
-		if (*endptr) {
-			p_err("can't parse %s as ID", **argv);
-			return -1;
-		}
-		NEXT_ARGP();
-
-		(*fds)[0] = bpf_prog_get_fd_by_id(id);
-		if ((*fds)[0] < 0) {
-			p_err("get by id (%u): %s", id, strerror(errno));
-			return -1;
-		}
-		return 1;
-	} else if (is_prefix(**argv, "tag")) {
-		unsigned char tag[BPF_TAG_SIZE];
-
-		NEXT_ARGP();
-
-		if (sscanf(**argv, BPF_TAG_FMT, tag, tag + 1, tag + 2,
-			   tag + 3, tag + 4, tag + 5, tag + 6, tag + 7)
-		    != BPF_TAG_SIZE) {
-			p_err("can't parse tag");
-			return -1;
-		}
-		NEXT_ARGP();
-
-		return prog_fd_by_nametag(tag, fds, true);
-	} else if (is_prefix(**argv, "name")) {
-		char *name;
-
-		NEXT_ARGP();
-
-		name = **argv;
-		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
-			p_err("can't parse name");
-			return -1;
-		}
-		NEXT_ARGP();
-
-		return prog_fd_by_nametag(name, fds, false);
-	} else if (is_prefix(**argv, "pinned")) {
-		char *path;
-
-		NEXT_ARGP();
-
-		path = **argv;
-		NEXT_ARGP();
-
-		(*fds)[0] = open_obj_pinned_any(path, BPF_OBJ_PROG);
-		if ((*fds)[0] < 0)
-			return -1;
-		return 1;
-	}
-
-	p_err("expected 'id', 'tag', 'name' or 'pinned', got: '%s'?", **argv);
-	return -1;
-}
-
-int prog_parse_fd(int *argc, char ***argv)
-{
-	int *fds = NULL;
-	int nb_fds, fd;
-
-	fds = malloc(sizeof(int));
-	if (!fds) {
-		p_err("mem alloc failed");
-		return -1;
-	}
-	nb_fds = prog_parse_fds(argc, argv, &fds);
-	if (nb_fds != 1) {
-		if (nb_fds > 1) {
-			p_err("several programs match this handle");
-			while (nb_fds--)
-				close(fds[nb_fds]);
-		}
-		fd = -1;
-		goto exit_free;
-	}
-
-	fd = fds[0];
-exit_free:
-	free(fds);
-	return fd;
-}
-
 static void show_prog_maps(int fd, __u32 num_maps)
 {
 	struct bpf_prog_info info = {};
@@ -342,6 +190,8 @@ static void print_prog_json(struct bpf_prog_info *info, int fd)
 		jsonw_end_array(json_wtr);
 	}
 
+	emit_obj_refs_json(&refs_table, info->id, json_wtr);
+
 	jsonw_end_object(json_wtr);
 }
 
@@ -408,6 +258,8 @@ static void print_prog_plain(struct bpf_prog_info *info, int fd)
 	if (info->btf_id)
 		printf("\n\tbtf_id %d", info->btf_id);
 
+	emit_obj_refs_plain(&refs_table, info->id, "\n\tpids ");
+
 	printf("\n");
 }
 
@@ -473,6 +325,7 @@ static int do_show(int argc, char **argv)
 
 	if (show_pinned)
 		build_pinned_obj_table(&prog_table, BPF_OBJ_PROG);
+	build_obj_refs_table(&refs_table, BPF_OBJ_PROG);
 
 	if (argc == 2)
 		return do_show_subset(argc, argv);
@@ -514,6 +367,8 @@ static int do_show(int argc, char **argv)
 	if (json_output)
 		jsonw_end_array(json_wtr);
 
+	delete_obj_refs_table(&refs_table);
+
 	return err;
 }
 

tools/bpf/bpftool/skeleton/pid_iter.bpf.c

+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/* Copyright (c) 2020 Facebook */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include <bpf/bpf_tracing.h>
+#include "pid_iter.h"
+
+/* keep in sync with the definition in main.h */
+enum bpf_obj_type {
+	BPF_OBJ_UNKNOWN,
+	BPF_OBJ_PROG,
+	BPF_OBJ_MAP,
+	BPF_OBJ_LINK,
+	BPF_OBJ_BTF,
+};
+
+extern const void bpf_link_fops __ksym;
+extern const void bpf_map_fops __ksym;
+extern const void bpf_prog_fops __ksym;
+extern const void btf_fops __ksym;
+
+const volatile enum bpf_obj_type obj_type = BPF_OBJ_UNKNOWN;
+
+static __always_inline __u32 get_obj_id(void *ent, enum bpf_obj_type type)
+{
+	switch (type) {
+	case BPF_OBJ_PROG:
+		return BPF_CORE_READ((struct bpf_prog *)ent, aux, id);
+	case BPF_OBJ_MAP:
+		return BPF_CORE_READ((struct bpf_map *)ent, id);
+	case BPF_OBJ_BTF:
+		return BPF_CORE_READ((struct btf *)ent, id);
+	case BPF_OBJ_LINK:
+		return BPF_CORE_READ((struct bpf_link *)ent, id);
+	default:
+		return 0;
+	}
+}
+
+SEC("iter/task_file")
+int iter(struct bpf_iter__task_file *ctx)
+{
+	struct file *file = ctx->file;
+	struct task_struct *task = ctx->task;
+	struct pid_iter_entry e;
+	const void *fops;
+
+	if (!file || !task)
+		return 0;
+
+	switch (obj_type) {
+	case BPF_OBJ_PROG:
+		fops = &bpf_prog_fops;
+		break;
+	case BPF_OBJ_MAP:
+		fops = &bpf_map_fops;
+		break;
+	case BPF_OBJ_BTF:
+		fops = &btf_fops;
+		break;
+	case BPF_OBJ_LINK:
+		fops = &bpf_link_fops;
+		break;
+	default:
+		return 0;
+	}
+
+	if (file->f_op != fops)
+		return 0;
+
+	e.pid = task->tgid;
+	e.id = get_obj_id(file->private_data, obj_type);
+	bpf_probe_read(&e.comm, sizeof(e.comm), task->group_leader->comm);
+	bpf_seq_write(ctx->meta->seq, &e, sizeof(e));
+
+	return 0;
+}
+
+char LICENSE[] SEC("license") = "Dual BSD/GPL";

tools/bpf/bpftool/skeleton/pid_iter.h

+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
+/* Copyright (c) 2020 Facebook */
+#ifndef __PID_ITER_H
+#define __PID_ITER_H
+
+struct pid_iter_entry {
+	__u32 id;
+	int pid;
+	char comm[16];
+};
+
+#endif

tools/bpf/bpftool/skeleton/profiler.bpf.c

 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (c) 2020 Facebook
-#include "profiler.h"
-#include <linux/bpf.h>
+#include <vmlinux.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_tracing.h>
 

tools/bpf/bpftool/skeleton/profiler.h

-/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
-#ifndef __PROFILER_H
-#define __PROFILER_H
-
-/* useful typedefs from vmlinux.h */
-
-typedef signed char __s8;
-typedef unsigned char __u8;
-typedef short int __s16;
-typedef short unsigned int __u16;
-typedef int __s32;
-typedef unsigned int __u32;
-typedef long long int __s64;
-typedef long long unsigned int __u64;
-
-typedef __s8 s8;
-typedef __u8 u8;
-typedef __s16 s16;
-typedef __u16 u16;
-typedef __s32 s32;
-typedef __u32 u32;
-typedef __s64 s64;
-typedef __u64 u64;
-
-enum {
-	false = 0,
-	true = 1,
-};
-
-#ifdef __CHECKER__
-#define __bitwise__ __attribute__((bitwise))
-#else
-#define __bitwise__
-#endif
-
-typedef __u16 __bitwise__ __le16;
-typedef __u16 __bitwise__ __be16;
-typedef __u32 __bitwise__ __le32;
-typedef __u32 __bitwise__ __be32;
-typedef __u64 __bitwise__ __le64;
-typedef __u64 __bitwise__ __be64;
-
-typedef __u16 __bitwise__ __sum16;
-typedef __u32 __bitwise__ __wsum;
-
-#endif /* __PROFILER_H */

tools/build/feature/Makefile

@@ -68,7 +68,7 @@ FILES=                                          \
          test-llvm-version.bin			\
          test-libaio.bin			\
          test-libzstd.bin			\
-         test-clang-bpf-global-var.bin		\
+         test-clang-bpf-co-re.bin		\
          test-file-handle.bin			\
          test-libpfm4.bin
 
@@ -325,7 +325,7 @@ $(OUTPUT)test-libaio.bin:
 $(OUTPUT)test-libzstd.bin:
 	$(BUILD) -lzstd
 
-$(OUTPUT)test-clang-bpf-global-var.bin:
+$(OUTPUT)test-clang-bpf-co-re.bin:
 	$(CLANG) -S -g -target bpf -o - $(patsubst %.bin,%.c,$(@F)) |	\
 		grep BTF_KIND_VAR
 

tools/build/feature/test-clang-bpf-global-var.c → tools/build/feature/test-clang-bpf-co-re.c

 // SPDX-License-Identifier: GPL-2.0
 // Copyright (c) 2020 Facebook
 
-volatile int global_value_for_test = 1;
+struct test {
+	int a;
+	int b;
+} __attribute__((preserve_access_index));
+
+volatile struct test global_value_for_test = {};

tools/lib/bpf/bpf_core_read.h

@@ -217,7 +217,7 @@ enum bpf_field_info_kind {
  */
 #define BPF_CORE_READ_INTO(dst, src, a, ...)				    \
 	({								    \
-		___core_read(bpf_core_read, dst, src, a, ##__VA_ARGS__)	    \
+		___core_read(bpf_core_read, dst, (src), a, ##__VA_ARGS__)   \
 	})
 
 /*
@@ -227,7 +227,7 @@ enum bpf_field_info_kind {
  */
 #define BPF_CORE_READ_STR_INTO(dst, src, a, ...)			    \
 	({								    \
-		___core_read(bpf_core_read_str, dst, src, a, ##__VA_ARGS__) \
+		___core_read(bpf_core_read_str, dst, (src), a, ##__VA_ARGS__)\
 	})
 
 /*
@@ -254,8 +254,8 @@ enum bpf_field_info_kind {
  */
 #define BPF_CORE_READ(src, a, ...)					    \
 	({								    \
-		___type(src, a, ##__VA_ARGS__) __r;			    \
-		BPF_CORE_READ_INTO(&__r, src, a, ##__VA_ARGS__);	    \
+		___type((src), a, ##__VA_ARGS__) __r;			    \
+		BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__);	    \
 		__r;							    \
 	})
 

tools/lib/bpf/bpf_helpers.h

@@ -75,5 +75,6 @@ enum libbpf_tristate {
 };
 
 #define __kconfig __attribute__((section(".kconfig")))
+#define __ksym __attribute__((section(".ksyms")))
 
 #endif

tools/lib/bpf/btf.h

@@ -168,6 +168,11 @@ static inline bool btf_kflag(const struct btf_type *t)
 	return BTF_INFO_KFLAG(t->info);
 }
 
+static inline bool btf_is_void(const struct btf_type *t)
+{
+	return btf_kind(t) == BTF_KIND_UNKN;
+}
+
 static inline bool btf_is_int(const struct btf_type *t)
 {
 	return btf_kind(t) == BTF_KIND_INT;

tools/lib/bpf/libbpf.c

@@ -285,6 +285,7 @@ struct bpf_struct_ops {
 #define BSS_SEC ".bss"
 #define RODATA_SEC ".rodata"
 #define KCONFIG_SEC ".kconfig"
+#define KSYMS_SEC ".ksyms"
 #define STRUCT_OPS_SEC ".struct_ops"
 
 enum libbpf_map_type {
@@ -330,24 +331,39 @@ struct bpf_map {
 
 enum extern_type {
 	EXT_UNKNOWN,
-	EXT_CHAR,
-	EXT_BOOL,
-	EXT_INT,
-	EXT_TRISTATE,
-	EXT_CHAR_ARR,
+	EXT_KCFG,
+	EXT_KSYM,
+};
+
+enum kcfg_type {
+	KCFG_UNKNOWN,
+	KCFG_CHAR,
+	KCFG_BOOL,
+	KCFG_INT,
+	KCFG_TRISTATE,
+	KCFG_CHAR_ARR,
 };
 
 struct extern_desc {
-	const char *name;
+	enum extern_type type;
 	int sym_idx;
 	int btf_id;
-	enum extern_type type;
+	int sec_btf_id;
+	const char *name;
+	bool is_set;
+	bool is_weak;
+	union {
+		struct {
+			enum kcfg_type type;
 			int sz;
 			int align;
 			int data_off;
 			bool is_signed;
-	bool is_weak;
-	bool is_set;
+		} kcfg;
+		struct {
+			unsigned long long addr;
+		} ksym;
+	};
 };
 
 static LIST_HEAD(bpf_objects_list);
@@ -1424,19 +1440,19 @@ static struct extern_desc *find_extern_by_name(const struct bpf_object *obj,
 	return NULL;
 }
 
-static int set_ext_value_tri(struct extern_desc *ext, void *ext_val,
+static int set_kcfg_value_tri(struct extern_desc *ext, void *ext_val,
 			      char value)
 {
-	switch (ext->type) {
-	case EXT_BOOL:
+	switch (ext->kcfg.type) {
+	case KCFG_BOOL:
 		if (value == 'm') {
-			pr_warn("extern %s=%c should be tristate or char\n",
+			pr_warn("extern (kcfg) %s=%c should be tristate or char\n",
 				ext->name, value);
 			return -EINVAL;
 		}
 		*(bool *)ext_val = value == 'y' ? true : false;
 		break;
-	case EXT_TRISTATE:
+	case KCFG_TRISTATE:
 		if (value == 'y')
 			*(enum libbpf_tristate *)ext_val = TRI_YES;
 		else if (value == 'm')
@@ -1444,14 +1460,14 @@ static int set_ext_value_tri(struct extern_desc *ext, void *ext_val,
 		else /* value == 'n' */
 			*(enum libbpf_tristate *)ext_val = TRI_NO;
 		break;
-	case EXT_CHAR:
+	case KCFG_CHAR:
 		*(char *)ext_val = value;
 		break;
-	case EXT_UNKNOWN:
-	case EXT_INT:
-	case EXT_CHAR_ARR:
+	case KCFG_UNKNOWN:
+	case KCFG_INT:
+	case KCFG_CHAR_ARR:
 	default:
-		pr_warn("extern %s=%c should be bool, tristate, or char\n",
+		pr_warn("extern (kcfg) %s=%c should be bool, tristate, or char\n",
 			ext->name, value);
 		return -EINVAL;
 	}
@@ -1459,29 +1475,29 @@ static int set_ext_value_tri(struct extern_desc *ext, void *ext_val,
 	return 0;
 }
 
-static int set_ext_value_str(struct extern_desc *ext, char *ext_val,
+static int set_kcfg_value_str(struct extern_desc *ext, char *ext_val,
 			      const char *value)
 {
 	size_t len;
 
-	if (ext->type != EXT_CHAR_ARR) {
-		pr_warn("extern %s=%s should char array\n", ext->name, value);
+	if (ext->kcfg.type != KCFG_CHAR_ARR) {
+		pr_warn("extern (kcfg) %s=%s should be char array\n", ext->name, value);
 		return -EINVAL;
 	}
 
 	len = strlen(value);
 	if (value[len - 1] != '"') {
-		pr_warn("extern '%s': invalid string config '%s'\n",
+		pr_warn("extern (kcfg) '%s': invalid string config '%s'\n",
 			ext->name, value);
 		return -EINVAL;
 	}
 
 	/* strip quotes */
 	len -= 2;
-	if (len >= ext->sz) {
-		pr_warn("extern '%s': long string config %s of (%zu bytes) truncated to %d bytes\n",
-			ext->name, value, len, ext->sz - 1);
-		len = ext->sz - 1;
+	if (len >= ext->kcfg.sz) {
+		pr_warn("extern (kcfg) '%s': long string config %s of (%zu bytes) truncated to %d bytes\n",
+			ext->name, value, len, ext->kcfg.sz - 1);
+		len = ext->kcfg.sz - 1;
 	}
 	memcpy(ext_val, value + 1, len);
 	ext_val[len] = '\0';
@@ -1508,11 +1524,11 @@ static int parse_u64(const char *value, __u64 *res)
 	return 0;
 }
 
-static bool is_ext_value_in_range(const struct extern_desc *ext, __u64 v)
+static bool is_kcfg_value_in_range(const struct extern_desc *ext, __u64 v)
 {
-	int bit_sz = ext->sz * 8;
+	int bit_sz = ext->kcfg.sz * 8;
 
-	if (ext->sz == 8)
+	if (ext->kcfg.sz == 8)
 		return true;
 
 	/* Validate that value stored in u64 fits in integer of `ext->sz`
@@ -1527,26 +1543,26 @@ static bool is_ext_value_in_range(const struct extern_desc *ext, __u64 v)
 	 *  For unsigned target integer, check that all the (64 - Y) bits are
 	 *  zero.
 	 */
-	if (ext->is_signed)
+	if (ext->kcfg.is_signed)
 		return v + (1ULL << (bit_sz - 1)) < (1ULL << bit_sz);
 	else
 		return (v >> bit_sz) == 0;
 }
 
-static int set_ext_value_num(struct extern_desc *ext, void *ext_val,
+static int set_kcfg_value_num(struct extern_desc *ext, void *ext_val,
 			      __u64 value)
 {
-	if (ext->type != EXT_INT && ext->type != EXT_CHAR) {
-		pr_warn("extern %s=%llu should be integer\n",
+	if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR) {
+		pr_warn("extern (kcfg) %s=%llu should be integer\n",
 			ext->name, (unsigned long long)value);
 		return -EINVAL;
 	}
-	if (!is_ext_value_in_range(ext, value)) {
-		pr_warn("extern %s=%llu value doesn't fit in %d bytes\n",
-			ext->name, (unsigned long long)value, ext->sz);
+	if (!is_kcfg_value_in_range(ext, value)) {
+		pr_warn("extern (kcfg) %s=%llu value doesn't fit in %d bytes\n",
+			ext->name, (unsigned long long)value, ext->kcfg.sz);
 		return -ERANGE;
 	}
-	switch (ext->sz) {
+	switch (ext->kcfg.sz) {
 		case 1: *(__u8 *)ext_val = value; break;
 		case 2: *(__u16 *)ext_val = value; break;
 		case 4: *(__u32 *)ext_val = value; break;
@@ -1592,30 +1608,30 @@ static int bpf_object__process_kconfig_line(struct bpf_object *obj,
 	if (!ext || ext->is_set)
 		return 0;
 
-	ext_val = data + ext->data_off;
+	ext_val = data + ext->kcfg.data_off;
 	value = sep + 1;
 
 	switch (*value) {
 	case 'y': case 'n': case 'm':
-		err = set_ext_value_tri(ext, ext_val, *value);
+		err = set_kcfg_value_tri(ext, ext_val, *value);
 		break;
 	case '"':
-		err = set_ext_value_str(ext, ext_val, value);
+		err = set_kcfg_value_str(ext, ext_val, value);
 		break;
 	default:
 		/* assume integer */
 		err = parse_u64(value, &num);
 		if (err) {
-			pr_warn("extern %s=%s should be integer\n",
+			pr_warn("extern (kcfg) %s=%s should be integer\n",
 				ext->name, value);
 			return err;
 		}
-		err = set_ext_value_num(ext, ext_val, num);
+		err = set_kcfg_value_num(ext, ext_val, num);
 		break;
 	}
 	if (err)
 		return err;
-	pr_debug("extern %s=%s\n", ext->name, value);
+	pr_debug("extern (kcfg) %s=%s\n", ext->name, value);
 	return 0;
 }
 
@@ -1686,16 +1702,20 @@ static int bpf_object__read_kconfig_mem(struct bpf_object *obj,
 
 static int bpf_object__init_kconfig_map(struct bpf_object *obj)
 {
-	struct extern_desc *last_ext;
+	struct extern_desc *last_ext = NULL, *ext;
 	size_t map_sz;
-	int err;
+	int i, err;
 
-	if (obj->nr_extern == 0)
-		return 0;
+	for (i = 0; i < obj->nr_extern; i++) {
+		ext = &obj->externs[i];
+		if (ext->type == EXT_KCFG)
+			last_ext = ext;
+	}
 
-	last_ext = &obj->externs[obj->nr_extern - 1];
-	map_sz = last_ext->data_off + last_ext->sz;
+	if (!last_ext)
+		return 0;
 
+	map_sz = last_ext->kcfg.data_off + last_ext->kcfg.sz;
 	err = bpf_object__init_internal_map(obj, LIBBPF_MAP_KCONFIG,
 					    obj->efile.symbols_shndx,
 					    NULL, map_sz);
@@ -2714,7 +2734,32 @@ static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
 	return -ENOENT;
 }
 
-static enum extern_type find_extern_type(const struct btf *btf, int id,
+static int find_extern_sec_btf_id(struct btf *btf, int ext_btf_id) {
+	const struct btf_var_secinfo *vs;
+	const struct btf_type *t;
+	int i, j, n;
+
+	if (!btf)
+		return -ESRCH;
+
+	n = btf__get_nr_types(btf);
+	for (i = 1; i <= n; i++) {
+		t = btf__type_by_id(btf, i);
+
+		if (!btf_is_datasec(t))
+			continue;
+
+		vs = btf_var_secinfos(t);
+		for (j = 0; j < btf_vlen(t); j++, vs++) {
+			if (vs->type == ext_btf_id)
+				return i;
+		}
+	}
+
+	return -ENOENT;
+}
+
+static enum kcfg_type find_kcfg_type(const struct btf *btf, int id,
 				     bool *is_signed)
 {
 	const struct btf_type *t;
@@ -2730,29 +2775,29 @@ static enum extern_type find_extern_type(const struct btf *btf, int id,
 		int enc = btf_int_encoding(t);
 
 		if (enc & BTF_INT_BOOL)
-			return t->size == 1 ? EXT_BOOL : EXT_UNKNOWN;
+			return t->size == 1 ? KCFG_BOOL : KCFG_UNKNOWN;
 		if (is_signed)
 			*is_signed = enc & BTF_INT_SIGNED;
 		if (t->size == 1)
-			return EXT_CHAR;
+			return KCFG_CHAR;
 		if (t->size < 1 || t->size > 8 || (t->size & (t->size - 1)))
-			return EXT_UNKNOWN;
-		return EXT_INT;
+			return KCFG_UNKNOWN;
+		return KCFG_INT;
 	}
 	case BTF_KIND_ENUM:
 		if (t->size != 4)
-			return EXT_UNKNOWN;
+			return KCFG_UNKNOWN;
 		if (strcmp(name, "libbpf_tristate"))
-			return EXT_UNKNOWN;
-		return EXT_TRISTATE;
+			return KCFG_UNKNOWN;
+		return KCFG_TRISTATE;
 	case BTF_KIND_ARRAY:
 		if (btf_array(t)->nelems == 0)
-			return EXT_UNKNOWN;
-		if (find_extern_type(btf, btf_array(t)->type, NULL) != EXT_CHAR)
-			return EXT_UNKNOWN;
-		return EXT_CHAR_ARR;
+			return KCFG_UNKNOWN;
+		if (find_kcfg_type(btf, btf_array(t)->type, NULL) != KCFG_CHAR)
+			return KCFG_UNKNOWN;
+		return KCFG_CHAR_ARR;
 	default:
-		return EXT_UNKNOWN;
+		return KCFG_UNKNOWN;
 	}
 }
 
@@ -2761,23 +2806,45 @@ static int cmp_externs(const void *_a, const void *_b)
 	const struct extern_desc *a = _a;
 	const struct extern_desc *b = _b;
 
+	if (a->type != b->type)
+		return a->type < b->type ? -1 : 1;
+
+	if (a->type == EXT_KCFG) {
 		/* descending order by alignment requirements */
-	if (a->align != b->align)
-		return a->align > b->align ? -1 : 1;
+		if (a->kcfg.align != b->kcfg.align)
+			return a->kcfg.align > b->kcfg.align ? -1 : 1;
 		/* ascending order by size, within same alignment class */
-	if (a->sz != b->sz)
-		return a->sz < b->sz ? -1 : 1;
+		if (a->kcfg.sz != b->kcfg.sz)
+			return a->kcfg.sz < b->kcfg.sz ? -1 : 1;
+	}
+
 	/* resolve ties by name */
 	return strcmp(a->name, b->name);
 }
 
+static int find_int_btf_id(const struct btf *btf)
+{
+	const struct btf_type *t;
+	int i, n;
+
+	n = btf__get_nr_types(btf);
+	for (i = 1; i <= n; i++) {
+		t = btf__type_by_id(btf, i);
+
+		if (btf_is_int(t) && btf_int_bits(t) == 32)
+			return i;
+	}
+
+	return 0;
+}
+
 static int bpf_object__collect_externs(struct bpf_object *obj)
 {
+	struct btf_type *sec, *kcfg_sec = NULL, *ksym_sec = NULL;
 	const struct btf_type *t;
 	struct extern_desc *ext;
-	int i, n, off, btf_id;
-	struct btf_type *sec;
-	const char *ext_name;
+	int i, n, off;
+	const char *ext_name, *sec_name;
 	Elf_Scn *scn;
 	GElf_Shdr sh;
 
@@ -2823,22 +2890,50 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 		ext->name = btf__name_by_offset(obj->btf, t->name_off);
 		ext->sym_idx = i;
 		ext->is_weak = GELF_ST_BIND(sym.st_info) == STB_WEAK;
-		ext->sz = btf__resolve_size(obj->btf, t->type);
-		if (ext->sz <= 0) {
-			pr_warn("failed to resolve size of extern '%s': %d\n",
-				ext_name, ext->sz);
-			return ext->sz;
-		}
-		ext->align = btf__align_of(obj->btf, t->type);
-		if (ext->align <= 0) {
-			pr_warn("failed to determine alignment of extern '%s': %d\n",
-				ext_name, ext->align);
-			return -EINVAL;
-		}
-		ext->type = find_extern_type(obj->btf, t->type,
-					     &ext->is_signed);
-		if (ext->type == EXT_UNKNOWN) {
-			pr_warn("extern '%s' type is unsupported\n", ext_name);
+
+		ext->sec_btf_id = find_extern_sec_btf_id(obj->btf, ext->btf_id);
+		if (ext->sec_btf_id <= 0) {
+			pr_warn("failed to find BTF for extern '%s' [%d] section: %d\n",
+				ext_name, ext->btf_id, ext->sec_btf_id);
+			return ext->sec_btf_id;
+		}
+		sec = (void *)btf__type_by_id(obj->btf, ext->sec_btf_id);
+		sec_name = btf__name_by_offset(obj->btf, sec->name_off);
+
+		if (strcmp(sec_name, KCONFIG_SEC) == 0) {
+			kcfg_sec = sec;
+			ext->type = EXT_KCFG;
+			ext->kcfg.sz = btf__resolve_size(obj->btf, t->type);
+			if (ext->kcfg.sz <= 0) {
+				pr_warn("failed to resolve size of extern (kcfg) '%s': %d\n",
+					ext_name, ext->kcfg.sz);
+				return ext->kcfg.sz;
+			}
+			ext->kcfg.align = btf__align_of(obj->btf, t->type);
+			if (ext->kcfg.align <= 0) {
+				pr_warn("failed to determine alignment of extern (kcfg) '%s': %d\n",
+					ext_name, ext->kcfg.align);
+				return -EINVAL;
+			}
+			ext->kcfg.type = find_kcfg_type(obj->btf, t->type,
+						        &ext->kcfg.is_signed);
+			if (ext->kcfg.type == KCFG_UNKNOWN) {
+				pr_warn("extern (kcfg) '%s' type is unsupported\n", ext_name);
+				return -ENOTSUP;
+			}
+		} else if (strcmp(sec_name, KSYMS_SEC) == 0) {
+			const struct btf_type *vt;
+
+			ksym_sec = sec;
+			ext->type = EXT_KSYM;
+
+			vt = skip_mods_and_typedefs(obj->btf, t->type, NULL);
+			if (!btf_is_void(vt)) {
+				pr_warn("extern (ksym) '%s' is not typeless (void)\n", ext_name);
+				return -ENOTSUP;
+			}
+		} else {
+			pr_warn("unrecognized extern section '%s'\n", sec_name);
 			return -ENOTSUP;
 		}
 	}
@@ -2847,25 +2942,63 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 	if (!obj->nr_extern)
 		return 0;
 
-	/* sort externs by (alignment, size, name) and calculate their offsets
-	 * within a map */
+	/* sort externs by type, for kcfg ones also by (align, size, name) */
 	qsort(obj->externs, obj->nr_extern, sizeof(*ext), cmp_externs);
-	off = 0;
+
+	/* for .ksyms section, we need to turn all externs into allocated
+	 * variables in BTF to pass kernel verification; we do this by
+	 * pretending that each extern is a 8-byte variable
+	 */
+	if (ksym_sec) {
+		/* find existing 4-byte integer type in BTF to use for fake
+		 * extern variables in DATASEC
+		 */
+		int int_btf_id = find_int_btf_id(obj->btf);
+
 		for (i = 0; i < obj->nr_extern; i++) {
 			ext = &obj->externs[i];
-		ext->data_off = roundup(off, ext->align);
-		off = ext->data_off + ext->sz;
-		pr_debug("extern #%d: symbol %d, off %u, name %s\n",
-			 i, ext->sym_idx, ext->data_off, ext->name);
+			if (ext->type != EXT_KSYM)
+				continue;
+			pr_debug("extern (ksym) #%d: symbol %d, name %s\n",
+				 i, ext->sym_idx, ext->name);
 		}
 
-	btf_id = btf__find_by_name(obj->btf, KCONFIG_SEC);
-	if (btf_id <= 0) {
-		pr_warn("no BTF info found for '%s' datasec\n", KCONFIG_SEC);
+		sec = ksym_sec;
+		n = btf_vlen(sec);
+		for (i = 0, off = 0; i < n; i++, off += sizeof(int)) {
+			struct btf_var_secinfo *vs = btf_var_secinfos(sec) + i;
+			struct btf_type *vt;
+
+			vt = (void *)btf__type_by_id(obj->btf, vs->type);
+			ext_name = btf__name_by_offset(obj->btf, vt->name_off);
+			ext = find_extern_by_name(obj, ext_name);
+			if (!ext) {
+				pr_warn("failed to find extern definition for BTF var '%s'\n",
+					ext_name);
 				return -ESRCH;
 			}
+			btf_var(vt)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
+			vt->type = int_btf_id;
+			vs->offset = off;
+			vs->size = sizeof(int);
+		}
+		sec->size = off;
+	}
+
+	if (kcfg_sec) {
+		sec = kcfg_sec;
+		/* for kcfg externs calculate their offsets within a .kconfig map */
+		off = 0;
+		for (i = 0; i < obj->nr_extern; i++) {
+			ext = &obj->externs[i];
+			if (ext->type != EXT_KCFG)
+				continue;
 
-	sec = (struct btf_type *)btf__type_by_id(obj->btf, btf_id);
+			ext->kcfg.data_off = roundup(off, ext->kcfg.align);
+			off = ext->kcfg.data_off + ext->kcfg.sz;
+			pr_debug("extern (kcfg) #%d: symbol %d, off %u, name %s\n",
+				 i, ext->sym_idx, ext->kcfg.data_off, ext->name);
+		}
 		sec->size = off;
 		n = btf_vlen(sec);
 		for (i = 0; i < n; i++) {
@@ -2879,10 +3012,10 @@ static int bpf_object__collect_externs(struct bpf_object *obj)
 					ext_name);
 				return -ESRCH;
 			}
-		vs->offset = ext->data_off;
 			btf_var(t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
+			vs->offset = ext->kcfg.data_off;
+		}
 	}
-
 	return 0;
 }
 
@@ -3012,11 +3145,11 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 				sym_idx);
 			return -LIBBPF_ERRNO__RELOC;
 		}
-		pr_debug("found extern #%d '%s' (sym %d, off %u) for insn %u\n",
-			 i, ext->name, ext->sym_idx, ext->data_off, insn_idx);
+		pr_debug("found extern #%d '%s' (sym %d) for insn %u\n",
+			 i, ext->name, ext->sym_idx, insn_idx);
 		reloc_desc->type = RELO_EXTERN;
 		reloc_desc->insn_idx = insn_idx;
-		reloc_desc->sym_off = ext->data_off;
+		reloc_desc->sym_off = i; /* sym_off stores extern index */
 		return 0;
 	}
 
@@ -4941,6 +5074,7 @@ bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
 	for (i = 0; i < prog->nr_reloc; i++) {
 		struct reloc_desc *relo = &prog->reloc_desc[i];
 		struct bpf_insn *insn = &prog->insns[relo->insn_idx];
+		struct extern_desc *ext;
 
 		if (relo->insn_idx + 1 >= (int)prog->insns_cnt) {
 			pr_warn("relocation out of range: '%s'\n",
@@ -4959,9 +5093,15 @@ bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
 			insn[0].imm = obj->maps[relo->map_idx].fd;
 			break;
 		case RELO_EXTERN:
+			ext = &obj->externs[relo->sym_off];
+			if (ext->type == EXT_KCFG) {
 				insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
 				insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
-			insn[1].imm = relo->sym_off;
+				insn[1].imm = ext->kcfg.data_off;
+			} else /* EXT_KSYM */ {
+				insn[0].imm = (__u32)ext->ksym.addr;
+				insn[1].imm = ext->ksym.addr >> 32;
+			}
 			break;
 		case RELO_CALL:
 			err = bpf_program__reloc_text(prog, obj, relo);
@@ -5580,56 +5720,114 @@ static int bpf_object__sanitize_maps(struct bpf_object *obj)
 	return 0;
 }
 
+static int bpf_object__read_kallsyms_file(struct bpf_object *obj)
+{
+	char sym_type, sym_name[500];
+	unsigned long long sym_addr;
+	struct extern_desc *ext;
+	int ret, err = 0;
+	FILE *f;
+
+	f = fopen("/proc/kallsyms", "r");
+	if (!f) {
+		err = -errno;
+		pr_warn("failed to open /proc/kallsyms: %d\n", err);
+		return err;
+	}
+
+	while (true) {
+		ret = fscanf(f, "%llx %c %499s%*[^\n]\n",
+			     &sym_addr, &sym_type, sym_name);
+		if (ret == EOF && feof(f))
+			break;
+		if (ret != 3) {
+			pr_warn("failed to read kallasyms entry: %d\n", ret);
+			err = -EINVAL;
+			goto out;
+		}
+
+		ext = find_extern_by_name(obj, sym_name);
+		if (!ext || ext->type != EXT_KSYM)
+			continue;
+
+		if (ext->is_set && ext->ksym.addr != sym_addr) {
+			pr_warn("extern (ksym) '%s' resolution is ambiguous: 0x%llx or 0x%llx\n",
+				sym_name, ext->ksym.addr, sym_addr);
+			err = -EINVAL;
+			goto out;
+		}
+		if (!ext->is_set) {
+			ext->is_set = true;
+			ext->ksym.addr = sym_addr;
+			pr_debug("extern (ksym) %s=0x%llx\n", sym_name, sym_addr);
+		}
+	}
+
+out:
+	fclose(f);
+	return err;
+}
+
 static int bpf_object__resolve_externs(struct bpf_object *obj,
 				       const char *extra_kconfig)
 {
-	bool need_config = false;
+	bool need_config = false, need_kallsyms = false;
 	struct extern_desc *ext;
+	void *kcfg_data = NULL;
 	int err, i;
-	void *data;
 
 	if (obj->nr_extern == 0)
 		return 0;
 
-	data = obj->maps[obj->kconfig_map_idx].mmaped;
+	if (obj->kconfig_map_idx >= 0)
+		kcfg_data = obj->maps[obj->kconfig_map_idx].mmaped;
 
 	for (i = 0; i < obj->nr_extern; i++) {
 		ext = &obj->externs[i];
 
-		if (strcmp(ext->name, "LINUX_KERNEL_VERSION") == 0) {
-			void *ext_val = data + ext->data_off;
+		if (ext->type == EXT_KCFG &&
+		    strcmp(ext->name, "LINUX_KERNEL_VERSION") == 0) {
+			void *ext_val = kcfg_data + ext->kcfg.data_off;
 			__u32 kver = get_kernel_version();
 
 			if (!kver) {
 				pr_warn("failed to get kernel version\n");
 				return -EINVAL;
 			}
-			err = set_ext_value_num(ext, ext_val, kver);
+			err = set_kcfg_value_num(ext, ext_val, kver);
 			if (err)
 				return err;
-			pr_debug("extern %s=0x%x\n", ext->name, kver);
-		} else if (strncmp(ext->name, "CONFIG_", 7) == 0) {
+			pr_debug("extern (kcfg) %s=0x%x\n", ext->name, kver);
+		} else if (ext->type == EXT_KCFG &&
+			   strncmp(ext->name, "CONFIG_", 7) == 0) {
 			need_config = true;
+		} else if (ext->type == EXT_KSYM) {
+			need_kallsyms = true;
 		} else {
 			pr_warn("unrecognized extern '%s'\n", ext->name);
 			return -EINVAL;
 		}
 	}
 	if (need_config && extra_kconfig) {
-		err = bpf_object__read_kconfig_mem(obj, extra_kconfig, data);
+		err = bpf_object__read_kconfig_mem(obj, extra_kconfig, kcfg_data);
 		if (err)
 			return -EINVAL;
 		need_config = false;
 		for (i = 0; i < obj->nr_extern; i++) {
 			ext = &obj->externs[i];
-			if (!ext->is_set) {
+			if (ext->type == EXT_KCFG && !ext->is_set) {
 				need_config = true;
 				break;
 			}
 		}
 	}
 	if (need_config) {
-		err = bpf_object__read_kconfig_file(obj, data);
+		err = bpf_object__read_kconfig_file(obj, kcfg_data);
+		if (err)
+			return -EINVAL;
+	}
+	if (need_kallsyms) {
+		err = bpf_object__read_kallsyms_file(obj);
 		if (err)
 			return -EINVAL;
 	}

tools/testing/selftests/bpf/prog_tests/ksyms.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <test_progs.h>
+#include "test_ksyms.skel.h"
+#include <sys/stat.h>
+
+static int duration;
+
+static __u64 kallsyms_find(const char *sym)
+{
+	char type, name[500];
+	__u64 addr, res = 0;
+	FILE *f;
+
+	f = fopen("/proc/kallsyms", "r");
+	if (CHECK(!f, "kallsyms_fopen", "failed to open: %d\n", errno))
+		return 0;
+
+	while (fscanf(f, "%llx %c %499s%*[^\n]\n", &addr, &type, name) > 0) {
+		if (strcmp(name, sym) == 0) {
+			res = addr;
+			goto out;
+		}
+	}
+
+	CHECK(false, "not_found", "symbol %s not found\n", sym);
+out:
+	fclose(f);
+	return res;
+}
+
+void test_ksyms(void)
+{
+	__u64 link_fops_addr = kallsyms_find("bpf_link_fops");
+	const char *btf_path = "/sys/kernel/btf/vmlinux";
+	struct test_ksyms *skel;
+	struct test_ksyms__data *data;
+	struct stat st;
+	__u64 btf_size;
+	int err;
+
+	if (CHECK(stat(btf_path, &st), "stat_btf", "err %d\n", errno))
+		return;
+	btf_size = st.st_size;
+
+	skel = test_ksyms__open_and_load();
+	if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
+		return;
+
+	err = test_ksyms__attach(skel);
+	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
+		goto cleanup;
+
+	/* trigger tracepoint */
+	usleep(1);
+
+	data = skel->data;
+	CHECK(data->out__bpf_link_fops != link_fops_addr, "bpf_link_fops",
+	      "got 0x%llx, exp 0x%llx\n",
+	      data->out__bpf_link_fops, link_fops_addr);
+	CHECK(data->out__bpf_link_fops1 != 0, "bpf_link_fops1",
+	      "got %llu, exp %llu\n", data->out__bpf_link_fops1, (__u64)0);
+	CHECK(data->out__btf_size != btf_size, "btf_size",
+	      "got %llu, exp %llu\n", data->out__btf_size, btf_size);
+	CHECK(data->out__per_cpu_start != 0, "__per_cpu_start",
+	      "got %llu, exp %llu\n", data->out__per_cpu_start, (__u64)0);
+
+cleanup:
+	test_ksyms__destroy(skel);
+}

tools/testing/selftests/bpf/progs/test_ksyms.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <stdbool.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+__u64 out__bpf_link_fops = -1;
+__u64 out__bpf_link_fops1 = -1;
+__u64 out__btf_size = -1;
+__u64 out__per_cpu_start = -1;
+
+extern const void bpf_link_fops __ksym;
+extern const void __start_BTF __ksym;
+extern const void __stop_BTF __ksym;
+extern const void __per_cpu_start __ksym;
+/* non-existing symbol, weak, default to zero */
+extern const void bpf_link_fops1 __ksym __weak;
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+	out__bpf_link_fops = (__u64)&bpf_link_fops;
+	out__btf_size = (__u64)(&__stop_BTF - &__start_BTF);
+	out__per_cpu_start = (__u64)&__per_cpu_start;
+
+	out__bpf_link_fops1 = (__u64)&bpf_link_fops1;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";