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libbpf: Cross-join available_filter_functions and kallsyms for multi-…
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…kprobes

When using regular expression matching with "kprobe multi", it scans all
the functions under "/proc/kallsyms" that can be matched. However, not all
of them can be traced by kprobe.multi. If any one of the functions fails
to be traced, it will result in the failure of all functions. The best
approach is to filter out the functions that cannot be traced to ensure
proper tracking of the functions.

Closes: https://lore.kernel.org/oe-kbuild-all/202307030355.TdXOHklM-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Jiri Olsa <jolsa@kernel.org>
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230705091209.3803873-1-liu.yun@linux.dev
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Jackie Liu authored and Andrii Nakryiko committed Jul 6, 2023
1 parent e76a014 commit 8a3fe76
Showing 1 changed file with 97 additions and 13 deletions.
110 changes: 97 additions & 13 deletions tools/lib/bpf/libbpf.c
Original file line number Diff line number Diff line change
Expand Up @@ -10228,6 +10228,12 @@ static const char *tracefs_uprobe_events(void)
return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events";
}

static const char *tracefs_available_filter_functions(void)
{
return use_debugfs() ? DEBUGFS"/available_filter_functions"
: TRACEFS"/available_filter_functions";
}

static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
const char *kfunc_name, size_t offset)
{
Expand Down Expand Up @@ -10543,25 +10549,107 @@ struct kprobe_multi_resolve {
size_t cnt;
};

static int
resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type,
const char *sym_name, void *ctx)
struct avail_kallsyms_data {
char **syms;
size_t cnt;
struct kprobe_multi_resolve *res;
};

static int avail_func_cmp(const void *a, const void *b)
{
struct kprobe_multi_resolve *res = ctx;
return strcmp(*(const char **)a, *(const char **)b);
}

static int avail_kallsyms_cb(unsigned long long sym_addr, char sym_type,
const char *sym_name, void *ctx)
{
struct avail_kallsyms_data *data = ctx;
struct kprobe_multi_resolve *res = data->res;
int err;

if (!glob_match(sym_name, res->pattern))
if (!bsearch(&sym_name, data->syms, data->cnt, sizeof(*data->syms), avail_func_cmp))
return 0;

err = libbpf_ensure_mem((void **) &res->addrs, &res->cap, sizeof(unsigned long),
res->cnt + 1);
err = libbpf_ensure_mem((void **)&res->addrs, &res->cap, sizeof(*res->addrs), res->cnt + 1);
if (err)
return err;

res->addrs[res->cnt++] = (unsigned long) sym_addr;
res->addrs[res->cnt++] = (unsigned long)sym_addr;
return 0;
}

static int libbpf_available_kallsyms_parse(struct kprobe_multi_resolve *res)
{
const char *available_functions_file = tracefs_available_filter_functions();
struct avail_kallsyms_data data;
char sym_name[500];
FILE *f;
int err = 0, ret, i;
char **syms = NULL;
size_t cap = 0, cnt = 0;

f = fopen(available_functions_file, "re");
if (!f) {
err = -errno;
pr_warn("failed to open %s: %d\n", available_functions_file, err);
return err;
}

while (true) {
char *name;

ret = fscanf(f, "%499s%*[^\n]\n", sym_name);
if (ret == EOF && feof(f))
break;

if (ret != 1) {
pr_warn("failed to parse available_filter_functions entry: %d\n", ret);
err = -EINVAL;
goto cleanup;
}

if (!glob_match(sym_name, res->pattern))
continue;

err = libbpf_ensure_mem((void **)&syms, &cap, sizeof(*syms), cnt + 1);
if (err)
goto cleanup;

name = strdup(sym_name);
if (!name) {
err = -errno;
goto cleanup;
}

syms[cnt++] = name;
}

/* no entries found, bail out */
if (cnt == 0) {
err = -ENOENT;
goto cleanup;
}

/* sort available functions */
qsort(syms, cnt, sizeof(*syms), avail_func_cmp);

data.syms = syms;
data.res = res;
data.cnt = cnt;
libbpf_kallsyms_parse(avail_kallsyms_cb, &data);

if (res->cnt == 0)
err = -ENOENT;

cleanup:
for (i = 0; i < cnt; i++)
free((char *)syms[i]);
free(syms);

fclose(f);
return err;
}

struct bpf_link *
bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
const char *pattern,
Expand Down Expand Up @@ -10598,13 +10686,9 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
return libbpf_err_ptr(-EINVAL);

if (pattern) {
err = libbpf_kallsyms_parse(resolve_kprobe_multi_cb, &res);
err = libbpf_available_kallsyms_parse(&res);
if (err)
goto error;
if (!res.cnt) {
err = -ENOENT;
goto error;
}
addrs = res.addrs;
cnt = res.cnt;
}
Expand Down

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