bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.

Add -L flag to bpftool to use libbpf gen_trace facility and syscall/loader program
for skeleton generation and program loading.

"bpftool gen skeleton -L" command will generate a "light skeleton" or "loader skeleton"
that is similar to existing skeleton, but has one major difference:
$ bpftool gen skeleton lsm.o > lsm.skel.h
$ bpftool gen skeleton -L lsm.o > lsm.lskel.h
$ diff lsm.skel.h lsm.lskel.h
@@ -5,34 +4,34 @@
 #define __LSM_SKEL_H__

 #include <stdlib.h>
-#include <bpf/libbpf.h>
+#include <bpf/bpf.h>

The light skeleton does not use majority of libbpf infrastructure.
It doesn't need libelf. It doesn't parse .o file.
It only needs few sys_bpf wrappers. All of them are in bpf/bpf.h file.
In future libbpf/bpf.c can be inlined into bpf.h, so not even libbpf.a would be
needed to work with light skeleton.

"bpftool prog load -L file.o" command is introduced for debugging of syscall/loader
program generation. Just like the same command without -L it will try to load
the programs from file.o into the kernel. It won't even try to pin them.

"bpftool prog load -L -d file.o" command will provide additional debug messages
on how syscall/loader program was generated.
Also the execution of syscall/loader program will use bpf_trace_printk() for
each step of loading BTF, creating maps, and loading programs.
The user can do "cat /.../trace_pipe" for further debug.

An example of fexit_sleep.lskel.h generated from progs/fexit_sleep.c:
struct fexit_sleep {
	struct bpf_loader_ctx ctx;
	struct {
		struct bpf_map_desc bss;
	} maps;
	struct {
		struct bpf_prog_desc nanosleep_fentry;
		struct bpf_prog_desc nanosleep_fexit;
	} progs;
	struct {
		int nanosleep_fentry_fd;
		int nanosleep_fexit_fd;
	} links;
	struct fexit_sleep__bss {
		int pid;
		int fentry_cnt;
		int fexit_cnt;
	} *bss;
};
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-18-alexei.starovoitov@gmail.com

tools/bpf/bpftool/Makefile

@@ -136,7 +136,7 @@ endif
 
 BPFTOOL_BOOTSTRAP := $(BOOTSTRAP_OUTPUT)bpftool
 
-BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o)
+BOOTSTRAP_OBJS = $(addprefix $(BOOTSTRAP_OUTPUT),main.o common.o json_writer.o gen.o btf.o xlated_dumper.o btf_dumper.o) $(OUTPUT)disasm.o
 OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
 
 VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)				\

tools/bpf/bpftool/main.c

@@ -29,6 +29,7 @@ bool show_pinned;
 bool block_mount;
 bool verifier_logs;
 bool relaxed_maps;
+bool use_loader;
 struct btf *base_btf;
 struct pinned_obj_table prog_table;
 struct pinned_obj_table map_table;
@@ -392,6 +393,7 @@ int main(int argc, char **argv)
 		{ "mapcompat",	no_argument,	NULL,	'm' },
 		{ "nomount",	no_argument,	NULL,	'n' },
 		{ "debug",	no_argument,	NULL,	'd' },
+		{ "use-loader",	no_argument,	NULL,	'L' },
 		{ "base-btf",	required_argument, NULL, 'B' },
 		{ 0 }
 	};
@@ -409,7 +411,7 @@ int main(int argc, char **argv)
 	hash_init(link_table.table);
 
 	opterr = 0;
-	while ((opt = getopt_long(argc, argv, "VhpjfmndB:",
+	while ((opt = getopt_long(argc, argv, "VhpjfLmndB:",
 				  options, NULL)) >= 0) {
 		switch (opt) {
 		case 'V':
@@ -452,6 +454,9 @@ int main(int argc, char **argv)
 				return -1;
 			}
 			break;
+		case 'L':
+			use_loader = true;
+			break;
 		default:
 			p_err("unrecognized option '%s'", argv[optind - 1]);
 			if (json_output)

tools/bpf/bpftool/main.h

@@ -90,6 +90,7 @@ extern bool show_pids;
 extern bool block_mount;
 extern bool verifier_logs;
 extern bool relaxed_maps;
+extern bool use_loader;
 extern struct btf *base_btf;
 extern struct pinned_obj_table prog_table;
 extern struct pinned_obj_table map_table;

tools/bpf/bpftool/prog.c

@@ -16,6 +16,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <dirent.h>
 
 #include <linux/err.h>
 #include <linux/perf_event.h>
@@ -24,6 +25,8 @@
 #include <bpf/bpf.h>
 #include <bpf/btf.h>
 #include <bpf/libbpf.h>
+#include <bpf/bpf_gen_internal.h>
+#include <bpf/skel_internal.h>
 
 #include "cfg.h"
 #include "main.h"
@@ -1499,7 +1502,7 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 	set_max_rlimit();
 
 	obj = bpf_object__open_file(file, &open_opts);
-	if (IS_ERR_OR_NULL(obj)) {
+	if (libbpf_get_error(obj)) {
 		p_err("failed to open object file");
 		goto err_free_reuse_maps;
 	}
@@ -1645,8 +1648,110 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 	return -1;
 }
 
+static int count_open_fds(void)
+{
+	DIR *dp = opendir("/proc/self/fd");
+	struct dirent *de;
+	int cnt = -3;
+
+	if (!dp)
+		return -1;
+
+	while ((de = readdir(dp)))
+		cnt++;
+
+	closedir(dp);
+	return cnt;
+}
+
+static int try_loader(struct gen_loader_opts *gen)
+{
+	struct bpf_load_and_run_opts opts = {};
+	struct bpf_loader_ctx *ctx;
+	int ctx_sz = sizeof(*ctx) + 64 * max(sizeof(struct bpf_map_desc),
+					     sizeof(struct bpf_prog_desc));
+	int log_buf_sz = (1u << 24) - 1;
+	int err, fds_before, fd_delta;
+	char *log_buf;
+
+	ctx = alloca(ctx_sz);
+	memset(ctx, 0, ctx_sz);
+	ctx->sz = ctx_sz;
+	ctx->log_level = 1;
+	ctx->log_size = log_buf_sz;
+	log_buf = malloc(log_buf_sz);
+	if (!log_buf)
+		return -ENOMEM;
+	ctx->log_buf = (long) log_buf;
+	opts.ctx = ctx;
+	opts.data = gen->data;
+	opts.data_sz = gen->data_sz;
+	opts.insns = gen->insns;
+	opts.insns_sz = gen->insns_sz;
+	fds_before = count_open_fds();
+	err = bpf_load_and_run(&opts);
+	fd_delta = count_open_fds() - fds_before;
+	if (err < 0) {
+		fprintf(stderr, "err %d\n%s\n%s", err, opts.errstr, log_buf);
+		if (fd_delta)
+			fprintf(stderr, "loader prog leaked %d FDs\n",
+				fd_delta);
+	}
+	free(log_buf);
+	return err;
+}
+
+static int do_loader(int argc, char **argv)
+{
+	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts);
+	DECLARE_LIBBPF_OPTS(gen_loader_opts, gen);
+	struct bpf_object_load_attr load_attr = {};
+	struct bpf_object *obj;
+	const char *file;
+	int err = 0;
+
+	if (!REQ_ARGS(1))
+		return -1;
+	file = GET_ARG();
+
+	obj = bpf_object__open_file(file, &open_opts);
+	if (libbpf_get_error(obj)) {
+		p_err("failed to open object file");
+		goto err_close_obj;
+	}
+
+	err = bpf_object__gen_loader(obj, &gen);
+	if (err)
+		goto err_close_obj;
+
+	load_attr.obj = obj;
+	if (verifier_logs)
+		/* log_level1 + log_level2 + stats, but not stable UAPI */
+		load_attr.log_level = 1 + 2 + 4;
+
+	err = bpf_object__load_xattr(&load_attr);
+	if (err) {
+		p_err("failed to load object file");
+		goto err_close_obj;
+	}
+
+	if (verifier_logs) {
+		struct dump_data dd = {};
+
+		kernel_syms_load(&dd);
+		dump_xlated_plain(&dd, (void *)gen.insns, gen.insns_sz, false, false);
+		kernel_syms_destroy(&dd);
+	}
+	err = try_loader(&gen);
+err_close_obj:
+	bpf_object__close(obj);
+	return err;
+}
+
 static int do_load(int argc, char **argv)
 {
+	if (use_loader)
+		return do_loader(argc, argv);
 	return load_with_options(argc, argv, true);
 }
 

tools/bpf/bpftool/xlated_dumper.c

@@ -196,6 +196,9 @@ static const char *print_imm(void *private_data,
 	else if (insn->src_reg == BPF_PSEUDO_MAP_VALUE)
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "map[id:%u][0]+%u", insn->imm, (insn + 1)->imm);
+	else if (insn->src_reg == BPF_PSEUDO_MAP_IDX_VALUE)
+		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
+			 "map[idx:%u]+%u", insn->imm, (insn + 1)->imm);
 	else if (insn->src_reg == BPF_PSEUDO_FUNC)
 		snprintf(dd->scratch_buff, sizeof(dd->scratch_buff),
 			 "subprog[%+d]", insn->imm);