Merge branch 'libbpf-extern-followups'

Andrii Nakryiko says:

====================
Based on latest feedback and discussions, this patch set implements the
following changes:

- Kconfig-provided externs have to be in .kconfig section, for which
  bpf_helpers.h provides convenient __kconfig macro (Daniel);
- instead of allowing to override Kconfig file path, switch this to ability to
  extend and override system Kconfig with user-provided custom values (Alexei);
- BTF is required when externs are used.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/gen.c

@@ -83,8 +83,8 @@ static const char *get_map_ident(const struct bpf_map *map)
 		return "rodata";
 	else if (str_has_suffix(name, ".bss"))
 		return "bss";
-	else if (str_has_suffix(name, ".extern"))
-		return "externs"; /* extern is a C keyword */
+	else if (str_has_suffix(name, ".kconfig"))
+		return "kconfig";
 	else
 		return NULL;
 }
@@ -112,8 +112,8 @@ static int codegen_datasec_def(struct bpf_object *obj,
 		sec_ident = "bss";
 	else if (strcmp(sec_name, ".rodata") == 0)
 		sec_ident = "rodata";
-	else if (strcmp(sec_name, ".extern") == 0)
-		sec_ident = "externs"; /* extern is a C keyword */
+	else if (strcmp(sec_name, ".kconfig") == 0)
+		sec_ident = "kconfig";
 	else
 		return 0;
 

tools/lib/bpf/bpf_helpers.h

@@ -53,4 +53,6 @@ enum libbpf_tristate {
 	TRI_MODULE = 2,
 };
 
+#define __kconfig __attribute__((section(".kconfig")))
+
 #endif

tools/lib/bpf/libbpf.h

@@ -85,12 +85,12 @@ struct bpf_object_open_opts {
 	 */
 	const char *pin_root_path;
 	__u32 attach_prog_fd;
-	/* kernel config file path override (for CONFIG_ externs); can point
-	 * to either uncompressed text file or .gz file
+	/* Additional kernel config content that augments and overrides
+	 * system Kconfig for CONFIG_xxx externs.
 	 */
-	const char *kconfig_path;
+	const char *kconfig;
 };
-#define bpf_object_open_opts__last_field kconfig_path
+#define bpf_object_open_opts__last_field kconfig
 
 LIBBPF_API struct bpf_object *bpf_object__open(const char *path);
 LIBBPF_API struct bpf_object *

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

@@ -23,19 +23,13 @@ static uint32_t get_kernel_version(void)
 static struct test_case {
 	const char *name;
 	const char *cfg;
-	const char *cfg_path;
 	bool fails;
 	struct test_core_extern__data data;
 } test_cases[] = {
-	{ .name = "default search path", .cfg_path = NULL,
-	  .data = { .bpf_syscall = true } },
-	{ .name = "/proc/config.gz", .cfg_path = "/proc/config.gz",
-	  .data = { .bpf_syscall = true } },
-	{ .name = "missing config", .fails = true,
-	  .cfg_path = "/proc/invalid-config.gz" },
+	{ .name = "default search path", .data = { .bpf_syscall = true } },
 	{
 		.name = "custom values",
-		.cfg = "CONFIG_BPF_SYSCALL=y\n"
+		.cfg = "CONFIG_BPF_SYSCALL=n\n"
 		       "CONFIG_TRISTATE=m\n"
 		       "CONFIG_BOOL=y\n"
 		       "CONFIG_CHAR=100\n"
@@ -45,7 +39,7 @@ static struct test_case {
 		       "CONFIG_STR=\"abracad\"\n"
 		       "CONFIG_MISSING=0",
 		.data = {
-			.bpf_syscall = true,
+			.bpf_syscall = false,
 			.tristate_val = TRI_MODULE,
 			.bool_val = true,
 			.char_val = 100,
@@ -133,30 +127,14 @@ void test_core_extern(void)
 	int n = sizeof(*skel->data) / sizeof(uint64_t);
 
 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
-		char tmp_cfg_path[] = "/tmp/test_core_extern_cfg.XXXXXX";
 		struct test_case *t = &test_cases[i];
 		DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
-			.kconfig_path = t->cfg_path,
+			.kconfig = t->cfg,
 		);
 
 		if (!test__start_subtest(t->name))
 			continue;
 
-		if (t->cfg) {
-			size_t n = strlen(t->cfg) + 1;
-			int fd = mkstemp(tmp_cfg_path);
-			int written;
-
-			if (CHECK(fd < 0, "mkstemp", "errno: %d\n", errno))
-				continue;
-			printf("using '%s' as config file\n", tmp_cfg_path);
-			written = write(fd, t->cfg, n);
-			close(fd);
-			if (CHECK_FAIL(written != n))
-				goto cleanup;
-			opts.kconfig_path = tmp_cfg_path;
-		}
-
 		skel = test_core_extern__open_opts(&opts);
 		if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
 			goto cleanup;
@@ -185,8 +163,6 @@ void test_core_extern(void)
 			       j, exp[j], got[j]);
 		}
 cleanup:
-		if (t->cfg)
-			unlink(tmp_cfg_path);
 		test_core_extern__destroy(skel);
 		skel = NULL;
 	}

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

@@ -15,20 +15,18 @@ void test_skeleton(void)
 	int duration = 0, err;
 	struct test_skeleton* skel;
 	struct test_skeleton__bss *bss;
-	struct test_skeleton__externs *exts;
+	struct test_skeleton__kconfig *kcfg;
 
 	skel = test_skeleton__open();
 	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
 		return;
 
-	printf("EXTERNS BEFORE: %p\n", skel->externs);
-	if (CHECK(skel->externs, "skel_externs", "externs are mmaped()!\n"))
+	if (CHECK(skel->kconfig, "skel_kconfig", "kconfig is mmaped()!\n"))
 		goto cleanup;
 
 	err = test_skeleton__load(skel);
 	if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
 		goto cleanup;
-	printf("EXTERNS AFTER: %p\n", skel->externs);
 
 	bss = skel->bss;
 	bss->in1 = 1;
@@ -37,7 +35,7 @@ void test_skeleton(void)
 	bss->in4 = 4;
 	bss->in5.a = 5;
 	bss->in5.b = 6;
-	exts = skel->externs;
+	kcfg = skel->kconfig;
 
 	err = test_skeleton__attach(skel);
 	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
@@ -55,10 +53,10 @@ void test_skeleton(void)
 	CHECK(bss->handler_out5.b != 6, "res6", "got %lld != exp %d\n",
 	      bss->handler_out5.b, 6);
 
-	CHECK(bss->bpf_syscall != exts->CONFIG_BPF_SYSCALL, "ext1",
-	      "got %d != exp %d\n", bss->bpf_syscall, exts->CONFIG_BPF_SYSCALL);
-	CHECK(bss->kern_ver != exts->LINUX_KERNEL_VERSION, "ext2",
-	      "got %d != exp %d\n", bss->kern_ver, exts->LINUX_KERNEL_VERSION);
+	CHECK(bss->bpf_syscall != kcfg->CONFIG_BPF_SYSCALL, "ext1",
+	      "got %d != exp %d\n", bss->bpf_syscall, kcfg->CONFIG_BPF_SYSCALL);
+	CHECK(bss->kern_ver != kcfg->LINUX_KERNEL_VERSION, "ext2",
+	      "got %d != exp %d\n", bss->kern_ver, kcfg->LINUX_KERNEL_VERSION);
 
 cleanup:
 	test_skeleton__destroy(skel);

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

@@ -10,16 +10,16 @@
 /* non-existing BPF helper, to test dead code elimination */
 static int (*bpf_missing_helper)(const void *arg1, int arg2) = (void *) 999;
 
-extern int LINUX_KERNEL_VERSION;
-extern bool CONFIG_BPF_SYSCALL; /* strong */
-extern enum libbpf_tristate CONFIG_TRISTATE __weak;
-extern bool CONFIG_BOOL __weak;
-extern char CONFIG_CHAR __weak;
-extern uint16_t CONFIG_USHORT __weak;
-extern int CONFIG_INT __weak;
-extern uint64_t CONFIG_ULONG __weak;
-extern const char CONFIG_STR[8] __weak;
-extern uint64_t CONFIG_MISSING __weak;
+extern int LINUX_KERNEL_VERSION __kconfig;
+extern bool CONFIG_BPF_SYSCALL __kconfig; /* strong */
+extern enum libbpf_tristate CONFIG_TRISTATE __kconfig __weak;
+extern bool CONFIG_BOOL __kconfig __weak;
+extern char CONFIG_CHAR __kconfig __weak;
+extern uint16_t CONFIG_USHORT __kconfig __weak;
+extern int CONFIG_INT __kconfig __weak;
+extern uint64_t CONFIG_ULONG __kconfig __weak;
+extern const char CONFIG_STR[8] __kconfig __weak;
+extern uint64_t CONFIG_MISSING __kconfig __weak;
 
 uint64_t kern_ver = -1;
 uint64_t bpf_syscall = -1;

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

@@ -21,8 +21,8 @@ char out3 = 0;
 long long out4 = 0;
 int out1 = 0;
 
-extern bool CONFIG_BPF_SYSCALL;
-extern int LINUX_KERNEL_VERSION;
+extern bool CONFIG_BPF_SYSCALL __kconfig;
+extern int LINUX_KERNEL_VERSION __kconfig;
 bool bpf_syscall = 0;
 int kern_ver = 0;