Commit 13d35a0c authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
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libbpf: Reduce reliance of attach_fns on sec_def internals 



Move closer to not relying on bpf_sec_def internals that won't be part
of public API, when pluggable SEC() handlers will be allowed. Drop
pre-calculated prefix length, and in various helpers don't rely on this
prefix length availability. Also minimize reliance on knowing
bpf_sec_def's prefix for few places where section prefix shortcuts are
supported (e.g., tp vs tracepoint, raw_tp vs raw_tracepoint).

Given checking some string for having a given string-constant prefix is
such a common operation and so annoying to be done with pure C code, add
a small macro helper, str_has_pfx(), and reuse it throughout libbpf.c
where prefix comparison is performed. With __builtin_constant_p() it's
possible to have a convenient helper that checks some string for having
a given prefix, where prefix is either string literal (or compile-time
known string due to compiler optimization) or just a runtime string
pointer, which is quite convenient and saves a lot of typing and string
literal duplication.

Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20210928161946.2512801-7-andrii@kernel.org
parent 12d9466d

tools/lib/bpf/libbpf.c

+23 −18
Original line number Diff line number Diff line
@@ -226,7 +226,6 @@ typedef struct bpf_link *(*attach_fn_t)(const struct bpf_program *prog, long coo 


struct bpf_sec_def {

	const char *sec;

	size_t len;

	enum bpf_prog_type prog_type;

	enum bpf_attach_type expected_attach_type;

	bool is_exp_attach_type_optional;
@@ -1671,7 +1670,7 @@ static int bpf_object__process_kconfig_line(struct bpf_object *obj, 
	void *ext_val;

	__u64 num;



	if (strncmp(buf, "CONFIG_", 7))

	if (!str_has_pfx(buf, "CONFIG_"))

		return 0;



	sep = strchr(buf, '=');
@@ -2920,7 +2919,7 @@ static Elf_Data *elf_sec_data(const struct bpf_object *obj, Elf_Scn *scn) 
static bool is_sec_name_dwarf(const char *name)

{

	/* approximation, but the actual list is too long */

	return strncmp(name, ".debug_", sizeof(".debug_") - 1) == 0;

	return str_has_pfx(name, ".debug_");

}



static bool ignore_elf_section(GElf_Shdr *hdr, const char *name)
@@ -2942,7 +2941,7 @@ static bool ignore_elf_section(GElf_Shdr *hdr, const char *name) 
	if (is_sec_name_dwarf(name))

		return true;



	if (strncmp(name, ".rel", sizeof(".rel") - 1) == 0) {

	if (str_has_pfx(name, ".rel")) {

		name += sizeof(".rel") - 1;

		/* DWARF section relocations */

		if (is_sec_name_dwarf(name))
@@ -6891,8 +6890,7 @@ static int bpf_object__resolve_externs(struct bpf_object *obj, 
			if (err)

				return err;

			pr_debug("extern (kcfg) %s=0x%x\n", ext->name, kver);

		} else if (ext->type == EXT_KCFG &&

			   strncmp(ext->name, "CONFIG_", 7) == 0) {

		} else if (ext->type == EXT_KCFG && str_has_pfx(ext->name, "CONFIG_")) {

			need_config = true;

		} else if (ext->type == EXT_KSYM) {

			if (ext->ksym.type_id)
@@ -7956,7 +7954,6 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog, 
			  attachable, attach_btf)			    \

	{								    \

		.sec = string,						    \

		.len = sizeof(string) - 1,				    \

		.prog_type = ptype,					    \

		.expected_attach_type = eatype,				    \

		.is_exp_attach_type_optional = eatype_optional,		    \
@@ -7987,7 +7984,6 @@ void bpf_program__set_expected_attach_type(struct bpf_program *prog, 


#define SEC_DEF(sec_pfx, ptype, ...) {					    \

	.sec = sec_pfx,							    \

	.len = sizeof(sec_pfx) - 1,					    \

	.prog_type = BPF_PROG_TYPE_##ptype,				    \

	.preload_fn = libbpf_preload_prog,				    \

	__VA_ARGS__							    \
@@ -8162,9 +8158,7 @@ static const struct bpf_sec_def *find_sec_def(const char *sec_name) 
	int i, n = ARRAY_SIZE(section_defs);



	for (i = 0; i < n; i++) {

		if (strncmp(sec_name,

			    section_defs[i].sec, section_defs[i].len))

			continue;

		if (str_has_pfx(sec_name, section_defs[i].sec))

			return &section_defs[i];

	}

	return NULL;
@@ -8519,7 +8513,7 @@ static int libbpf_find_attach_btf_id(struct bpf_program *prog, int *btf_obj_fd, 
			prog->sec_name);

		return -ESRCH;

	}

	attach_name = prog->sec_name + prog->sec_def->len;

	attach_name = prog->sec_name + strlen(prog->sec_def->sec);



	/* BPF program's BTF ID */

	if (attach_prog_fd) {
@@ -9479,8 +9473,11 @@ static struct bpf_link *attach_kprobe(const struct bpf_program *prog, long cooki 
	char *func;

	int n, err;



	func_name = prog->sec_name + prog->sec_def->len;

	opts.retprobe = strcmp(prog->sec_def->sec, "kretprobe/") == 0;

	opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe/");

	if (opts.retprobe)

		func_name = prog->sec_name + sizeof("kretprobe/") - 1;

	else

		func_name = prog->sec_name + sizeof("kprobe/") - 1;



	n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);

	if (n < 1) {
@@ -9762,8 +9759,11 @@ static struct bpf_link *attach_tp(const struct bpf_program *prog, long cookie) 
	if (!sec_name)

		return libbpf_err_ptr(-ENOMEM);



	/* extract "tp/<category>/<name>" */

	tp_cat = sec_name + prog->sec_def->len;

	/* extract "tp/<category>/<name>" or "tracepoint/<category>/<name>" */

	if (str_has_pfx(prog->sec_name, "tp/"))

		tp_cat = sec_name + sizeof("tp/") - 1;

	else

		tp_cat = sec_name + sizeof("tracepoint/") - 1;

	tp_name = strchr(tp_cat, '/');

	if (!tp_name) {

		free(sec_name);
@@ -9809,7 +9809,12 @@ struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *pr 


static struct bpf_link *attach_raw_tp(const struct bpf_program *prog, long cookie)

{

	const char *tp_name = prog->sec_name + prog->sec_def->len;

	const char *tp_name;



	if (str_has_pfx(prog->sec_name, "raw_tp/"))

		tp_name = prog->sec_name + sizeof("raw_tp/") - 1;

	else

		tp_name = prog->sec_name + sizeof("raw_tracepoint/") - 1;



	return bpf_program__attach_raw_tracepoint(prog, tp_name);

}

tools/lib/bpf/libbpf_internal.h

+7 −0
Original line number Diff line number Diff line
@@ -89,6 +89,13 @@ 
	(offsetof(TYPE, FIELD) + sizeof(((TYPE *)0)->FIELD))

#endif



/* Check whether a string `str` has prefix `pfx`, regardless if `pfx` is

 * a string literal known at compilation time or char * pointer known only at

 * runtime.

 */

#define str_has_pfx(str, pfx) \

	(strncmp(str, pfx, __builtin_constant_p(pfx) ? sizeof(pfx) - 1 : strlen(pfx)) == 0)



/* Symbol versioning is different between static and shared library.

 * Properly versioned symbols are needed for shared library, but

 * only the symbol of the new version is needed for static library.