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libbpf: attempt to load kernel BTF from sysfs first 

Add support for loading kernel BTF from sysfs (/sys/kernel/btf/vmlinux)
as a target BTF. Also extend the list of on disk search paths for
vmlinux ELF image with entries that perf is searching for.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Andrii Nakryiko 2019-08-13 11:54:43 -07:00 committed by Daniel Borkmann
parent 7fd785685e
commit a1916a153c
1 changed files with 57 additions and 7 deletions
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64
tools/lib/bpf/libbpf.c
View File

@ -2807,15 +2807,61 @@ static int bpf_core_reloc_insn(struct bpf_program *prog, int insn_off,
return 0;
}
static struct btf *btf_load_raw(const char *path)
{
struct btf *btf;
size_t read_cnt;
struct stat st;
void *data;
FILE *f;
if (stat(path, &st))
return ERR_PTR(-errno);
data = malloc(st.st_size);
if (!data)
return ERR_PTR(-ENOMEM);
f = fopen(path, "rb");
if (!f) {
btf = ERR_PTR(-errno);
goto cleanup;
}
read_cnt = fread(data, 1, st.st_size, f);
fclose(f);
if (read_cnt < st.st_size) {
btf = ERR_PTR(-EBADF);
goto cleanup;
}
btf = btf__new(data, read_cnt);
cleanup:
free(data);
return btf;
}
/*
* Probe few well-known locations for vmlinux kernel image and try to load BTF
* data out of it to use for target BTF.
*/
static struct btf *bpf_core_find_kernel_btf(void)
{
const char *locations[] = {
"/lib/modules/%1$s/vmlinux-%1$s",
"/usr/lib/modules/%1$s/kernel/vmlinux",
struct {
const char *path_fmt;
bool raw_btf;
} locations[] = {
/* try canonical vmlinux BTF through sysfs first */
{ "/sys/kernel/btf/vmlinux", true /* raw BTF */ },
/* fall back to trying to find vmlinux ELF on disk otherwise */
{ "/boot/vmlinux-%1$s" },
{ "/lib/modules/%1$s/vmlinux-%1$s" },
{ "/lib/modules/%1$s/build/vmlinux" },
{ "/usr/lib/modules/%1$s/kernel/vmlinux" },
{ "/usr/lib/debug/boot/vmlinux-%1$s" },
{ "/usr/lib/debug/boot/vmlinux-%1$s.debug" },
{ "/usr/lib/debug/lib/modules/%1$s/vmlinux" },
};
char path[PATH_MAX + 1];
struct utsname buf;
@ -2825,14 +2871,18 @@ static struct btf *bpf_core_find_kernel_btf(void)
uname(&buf);
for (i = 0; i < ARRAY_SIZE(locations); i++) {
snprintf(path, PATH_MAX, locations[i], buf.release);
snprintf(path, PATH_MAX, locations[i].path_fmt, buf.release);
if (access(path, R_OK))
continue;
btf = btf__parse_elf(path, NULL);
pr_debug("kernel BTF load from '%s': %ld\n",
path, PTR_ERR(btf));
if (locations[i].raw_btf)
btf = btf_load_raw(path);
else
btf = btf__parse_elf(path, NULL);
pr_debug("loading kernel BTF '%s': %ld\n",
path, IS_ERR(btf) ? PTR_ERR(btf) : 0);
if (IS_ERR(btf))
continue;