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libbpf: Reduce reliance of attach_fns on sec_def internals

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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: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/bpf/20210928161946.2512801-7-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-09-28 09:19:42 -07:00 • committed by Alexei Starovoitov
parent 12d9466d8b
commit 13d35a0cf1
2 changed files with 30 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

41
tools/lib/bpf/libbpf.c
View file

@ -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__ \
@ -8162,10 +8158,8 @@ 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;
return &section_defs[i];
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);
}

7
tools/lib/bpf/libbpf_internal.h
View file

@ -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.