[PATCH v1 6/9] perf symbol: Use fallbacks with filename__read_build_id

Ian Rogers
2025-11-23T02:32:40Z

Try libbfd, libelf and then symbol-minimal when trying to read a build
ID. Always compile in symbol-minimal so that it is the fallback of
last resort. Rename libelf reading code. Move the decompression code
into symbol.c and allow its use with the symbol-minimal version.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/Build | 5 +-
tools/perf/util/libbfd.c | 4 +-
tools/perf/util/libbfd.h | 8 +-
tools/perf/util/perf-libelf.c | 113 +++++++++++++++++++++++
tools/perf/util/perf-libelf.h | 20 ++++
tools/perf/util/symbol-elf.c | 154 +------------------------------
tools/perf/util/symbol-minimal.c | 12 ++-
tools/perf/util/symbol-minimal.h | 9 ++
tools/perf/util/symbol.c | 50 ++++++++++
9 files changed, 210 insertions(+), 165 deletions(-)
create mode 100644 tools/perf/util/symbol-minimal.h

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index dcac6f1e1d99..c40053db2212 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -54,6 +54,7 @@ perf-util-y += usage.o
perf-util-y += dso.o
perf-util-y += dsos.o
perf-util-y += symbol.o
+perf-util-y += symbol-minimal.o
perf-util-y += symbol_fprintf.o
perf-util-y += map_symbol.o
perf-util-y += color.o
@@ -209,10 +210,6 @@ ifdef hashmap
perf-util-y += hashmap.o
endif

-ifndef CONFIG_LIBELF
-perf-util-y += symbol-minimal.o
-endif
-
ifndef CONFIG_SETNS
perf-util-y += setns.o
endif
diff --git a/tools/perf/util/libbfd.c b/tools/perf/util/libbfd.c
index 6434c2dccd4a..c438fbd03b24 100644
--- a/tools/perf/util/libbfd.c
+++ b/tools/perf/util/libbfd.c
@@ -418,13 +418,13 @@ int dso__load_bfd_symbols(struct dso *dso, const char *debugfile)
return err;
}

-int libbfd__read_build_id(const char *filename, struct build_id *bid, bool block)
+int libbfd__read_build_id(int _fd, const char *filename, struct build_id *bid)
{
size_t size = sizeof(bid->data);
int err = -1, fd;
bfd *abfd;

- fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
+ fd = dup(_fd);
if (fd < 0)
return -1;

diff --git a/tools/perf/util/libbfd.h b/tools/perf/util/libbfd.h
index 5b5149516f1a..72f1ad9a7578 100644
--- a/tools/perf/util/libbfd.h
+++ b/tools/perf/util/libbfd.h
@@ -26,7 +26,7 @@ int dso__load_bfd_symbols(struct dso *dso, const char *debugfile);
int symbol__disassemble_libbfd(const char *filename, struct symbol *sym,
struct annotate_args *args);

-int libbfd__read_build_id(const char *filename, struct build_id *bid, bool block);
+int libbfd__read_build_id(int fd, const char *filename, struct build_id *bid);

int libbfd_filename__read_debuglink(const char *filename, char *debuglink, size_t size);

@@ -65,9 +65,9 @@ static inline int symbol__disassemble_libbfd(const char *filename __always_unuse
return -1;
}

-static inline int libbfd__read_build_id(const char *filename __always_unused,
- struct build_id *bid __always_unused,
- bool block __always_unused)
+static inline int libbfd__read_build_id(int fd __always_unused,
+ const char *filename __always_unused,
+ struct build_id *bid __always_unused)
{
return -1;
}
diff --git a/tools/perf/util/perf-libelf.c b/tools/perf/util/perf-libelf.c
index abd55bd7f14b..c7fa08a177d0 100644
--- a/tools/perf/util/perf-libelf.c
+++ b/tools/perf/util/perf-libelf.c
@@ -3,6 +3,10 @@

#include <stddef.h>
#include <string.h>
+#include <unistd.h>
+
+#include "build-id.h"
+#include "debug.h"

Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
GElf_Shdr *shp, const char *name, size_t *idx)
@@ -30,3 +34,112 @@ Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
return NULL;
}

+int __libelf__read_build_id(Elf *elf, void *bf, size_t size)
+{
+ int err = -1;
+ GElf_Ehdr ehdr;
+ GElf_Shdr shdr;
+ Elf_Data *data;
+ Elf_Scn *sec;
+ Elf_Kind ek;
+ void *ptr;
+
+ if (size < BUILD_ID_SIZE)
+ goto out;
+
+ ek = elf_kind(elf);
+ if (ek != ELF_K_ELF)
+ goto out;
+
+ if (gelf_getehdr(elf, &ehdr) == NULL) {
+ pr_err("%s: cannot get elf header.\n", __func__);
+ goto out;
+ }
+
+ /*
+ * Check following sections for notes:
+ * '.note.gnu.build-id'
+ * '.notes'
+ * '.note' (VDSO specific)
+ */
+ do {
+ sec = elf_section_by_name(elf, &ehdr, &shdr,
+ ".note.gnu.build-id", NULL);
+ if (sec)
+ break;
+
+ sec = elf_section_by_name(elf, &ehdr, &shdr,
+ ".notes", NULL);
+ if (sec)
+ break;
+
+ sec = elf_section_by_name(elf, &ehdr, &shdr,
+ ".note", NULL);
+ if (sec)
+ break;
+
+ return err;
+
+ } while (0);
+
+ data = elf_getdata(sec, NULL);
+ if (data == NULL)
+ goto out;
+
+ ptr = data->d_buf;
+ while (ptr < (data->d_buf + data->d_size)) {
+ GElf_Nhdr *nhdr = ptr;
+ size_t namesz = NOTE_ALIGN(nhdr->n_namesz),
+ descsz = NOTE_ALIGN(nhdr->n_descsz);
+ const char *name;
+
+ ptr += sizeof(*nhdr);
+ name = ptr;
+ ptr += namesz;
+ if (nhdr->n_type == NT_GNU_BUILD_ID &&
+ nhdr->n_namesz == sizeof("GNU")) {
+ if (memcmp(name, "GNU", sizeof("GNU")) == 0) {
+ size_t sz = min(size, descsz);
+
+ memcpy(bf, ptr, sz);
+ memset(bf + sz, 0, size - sz);
+ err = sz;
+ break;
+ }
+ }
+ ptr += descsz;
+ }
+
+out:
+ return err;
+}
+
+int libelf__read_build_id(int _fd, const char *filename, struct build_id *bid)
+{
+ size_t size = sizeof(bid->data);
+ int fd, err = -1;
+ Elf *elf;
+
+ if (size < BUILD_ID_SIZE)
+ goto out;
+
+ fd = dup(_fd);
+ if (fd < 0)
+ goto out;
+
+ elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+ if (elf == NULL) {
+ pr_debug2("%s: cannot read %s ELF file.\n", __func__, filename);
+ goto out_close;
+ }
+
+ err = __libelf__read_build_id(elf, bid->data, size);
+ if (err > 0)
+ bid->size = err;
+
+ elf_end(elf);
+out_close:
+ close(fd);
+out:
+ return err;
+}
diff --git a/tools/perf/util/perf-libelf.h b/tools/perf/util/perf-libelf.h
index 5d7d18daf5ff..931597493b1f 100644
--- a/tools/perf/util/perf-libelf.h
+++ b/tools/perf/util/perf-libelf.h
@@ -2,6 +2,8 @@
#ifndef __PERF_LIBELF_H
#define __PERF_LIBELF_H

+struct build_id;
+
#ifdef HAVE_LIBELF_SUPPORT

#include <libelf.h>
@@ -17,9 +19,27 @@
# define PERF_ELF_C_READ_MMAP ELF_C_READ
#endif

+/*
+ * Align offset to 4 bytes as needed for note name and descriptor data.
+ */
+#define NOTE_ALIGN(n) (((n) + 3) & -4U)
+
Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep, GElf_Shdr *shp, const char *name,
size_t *idx);

+int __libelf__read_build_id(Elf *elf, void *bf, size_t size);
+
+int libelf__read_build_id(int _fd, const char *filename, struct build_id *bid);
+
+#else // !defined(HAVE_LIBELF_SUPPORT)
+
+static inline int libelf__read_build_id(int fd __always_unused,
+ const char *filename __always_unused,
+ struct build_id *bid __always_unused)
+{
+ return -1;
+}
+
#endif // defined(HAVE_LIBELF_SUPPORT)

#endif /* __PERF_LIBELF_H */
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 750a30b216d6..b301f1263ecc 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -751,158 +751,6 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss)
return 0;
}

-/*
- * Align offset to 4 bytes as needed for note name and descriptor data.
- */
-#define NOTE_ALIGN(n) (((n) + 3) & -4U)
-
-static int elf_read_build_id(Elf *elf, void *bf, size_t size)
-{
- int err = -1;
- GElf_Ehdr ehdr;
- GElf_Shdr shdr;
- Elf_Data *data;
- Elf_Scn *sec;
- Elf_Kind ek;
- void *ptr;
-
- if (size < BUILD_ID_SIZE)
- goto out;
-
- ek = elf_kind(elf);
- if (ek != ELF_K_ELF)
- goto out;
-
- if (gelf_getehdr(elf, &ehdr) == NULL) {
- pr_err("%s: cannot get elf header.\n", __func__);
- goto out;
- }
-
- /*
- * Check following sections for notes:
- * '.note.gnu.build-id'
- * '.notes'
- * '.note' (VDSO specific)
- */
- do {
- sec = elf_section_by_name(elf, &ehdr, &shdr,
- ".note.gnu.build-id", NULL);
- if (sec)
- break;
-
- sec = elf_section_by_name(elf, &ehdr, &shdr,
- ".notes", NULL);
- if (sec)
- break;
-
- sec = elf_section_by_name(elf, &ehdr, &shdr,
- ".note", NULL);
- if (sec)
- break;
-
- return err;
-
- } while (0);
-
- data = elf_getdata(sec, NULL);
- if (data == NULL)
- goto out;
-
- ptr = data->d_buf;
- while (ptr < (data->d_buf + data->d_size)) {
- GElf_Nhdr *nhdr = ptr;
- size_t namesz = NOTE_ALIGN(nhdr->n_namesz),
- descsz = NOTE_ALIGN(nhdr->n_descsz);
- const char *name;
-
- ptr += sizeof(*nhdr);
- name = ptr;
- ptr += namesz;
- if (nhdr->n_type == NT_GNU_BUILD_ID &&
- nhdr->n_namesz == sizeof("GNU")) {
- if (memcmp(name, "GNU", sizeof("GNU")) == 0) {
- size_t sz = min(size, descsz);
- memcpy(bf, ptr, sz);
- memset(bf + sz, 0, size - sz);
- err = sz;
- break;
- }
- }
- ptr += descsz;
- }
-
-out:
- return err;
-}
-
-static int read_build_id(const char *filename, struct build_id *bid, bool block)
-{
- size_t size = sizeof(bid->data);
- int fd, err;
- Elf *elf;
-
- err = libbfd__read_build_id(filename, bid, block);
- if (err >= 0)
- goto out;
-
- if (size < BUILD_ID_SIZE)
- goto out;
-
- fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
- if (fd < 0)
- goto out;
-
- elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
- if (elf == NULL) {
- pr_debug2("%s: cannot read %s ELF file.\n", __func__, filename);
- goto out_close;
- }
-
- err = elf_read_build_id(elf, bid->data, size);
- if (err > 0)
- bid->size = err;
-
- elf_end(elf);
-out_close:
- close(fd);
-out:
- return err;
-}
-
-int filename__read_build_id(const char *filename, struct build_id *bid, bool block)
-{
- struct kmod_path m = { .name = NULL, };
- char path[PATH_MAX];
- int err;
-
- if (!filename)
- return -EFAULT;
-
- err = kmod_path__parse(&m, filename);
- if (err)
- return -1;
-
- if (m.comp) {
- int error = 0, fd;
-
- fd = filename__decompress(filename, path, sizeof(path), m.comp, &error);
- if (fd < 0) {
- pr_debug("Failed to decompress (error %d) %s\n",
- error, filename);
- return -1;
- }
- close(fd);
- filename = path;
- block = true;
- }
-
- err = read_build_id(filename, bid, block);
-
- if (m.comp)
- unlink(filename);
- return err;
-}
-
int sysfs__read_build_id(const char *filename, struct build_id *bid)
{
size_t size = sizeof(bid->data);
@@ -1170,7 +1018,7 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
struct build_id bid;
int size;

- size = elf_read_build_id(elf, build_id, BUILD_ID_SIZE);
+ size = __libelf__read_build_id(elf, build_id, BUILD_ID_SIZE);
if (size <= 0) {
*dso__load_errno(dso) = DSO_LOAD_ERRNO__CANNOT_READ_BUILDID;
goto out_elf_end;
diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
index aeb253248895..f9adeb09ef00 100644
--- a/tools/perf/util/symbol-minimal.c
+++ b/tools/perf/util/symbol-minimal.c
@@ -1,5 +1,7 @@
+#include "debug.h"
#include "dso.h"
#include "symbol.h"
+#include "symbol-minimal.h"
#include "symsrc.h"

#include <errno.h>
@@ -75,17 +77,19 @@ static int read_build_id(void *note_data, size_t note_len, struct build_id *bid,
return -1;
}

+#ifndef HAVE_LIBELF_SUPPORT
int filename__read_debuglink(const char *filename __maybe_unused,
char *debuglink __maybe_unused,
size_t size __maybe_unused)
{
return -1;
}
+#endif

/*
* Just try PT_NOTE header otherwise fails
*/
-int filename__read_build_id(const char *filename, struct build_id *bid, bool block)
+int sym_min__read_build_id(int _fd, const char *filename, struct build_id *bid)
{
int fd, ret = -1;
bool need_swap = false, elf32;
@@ -102,7 +106,7 @@ int filename__read_build_id(const char *filename, struct build_id *bid, bool blo
void *phdr, *buf = NULL;
ssize_t phdr_size, ehdr_size, buf_size = 0;

- fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
+ fd = dup(_fd);
if (fd < 0)
return -1;

@@ -194,9 +198,12 @@ int filename__read_build_id(const char *filename, struct build_id *bid, bool blo
free(phdr);
out:
close(fd);
+ if (ret)
+ pr_debug("Error reading build-id from %s\n", filename);
return ret;
}

+#ifndef HAVE_LIBELF_SUPPORT
int sysfs__read_build_id(const char *filename, struct build_id *bid)
{
int fd;
@@ -358,3 +365,4 @@ bool filename__has_section(const char *filename __maybe_unused, const char *sec
{
return false;
}
+#endif // HAVE_LIBELF_SUPPORT
diff --git a/tools/perf/util/symbol-minimal.h b/tools/perf/util/symbol-minimal.h
new file mode 100644
index 000000000000..185d98968212
--- /dev/null
+++ b/tools/perf/util/symbol-minimal.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_SYMBOL_MINIMAL_H
+#define __PERF_SYMBOL_MINIMAL_H
+
+struct build_id;
+
+int sym_min__read_build_id(int _fd, const char *filename, struct build_id *bid);
+
+#endif /* __PERF_SYMBOL_MINIMAL_H */
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 638015651547..c8795e1da2df 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -35,6 +35,7 @@
#include "path.h"
#include "perf-libelf.h"
#include "strlist.h"
+#include "symbol-minimal.h"
#include "symbol.h"
#include "symsrc.h"
#include "util.h" // lsdir()
@@ -1999,6 +2000,55 @@ static bool filename__readable(const char *file)
return true;
}

+int filename__read_build_id(const char *filename, struct build_id *bid, bool block)
+{
+ struct kmod_path m = { .name = NULL, };
+ char path[PATH_MAX];
+ int err, fd;
+
+ if (!filename)
+ return -EFAULT;
+
+ err = kmod_path__parse(&m, filename);
+ if (err)
+ return -1;
+
+ if (m.comp) {
+ int error = 0;
+
+ fd = filename__decompress(filename, path, sizeof(path), m.comp, &error);
+ if (fd < 0) {
+ pr_debug("Failed to decompress (error %d) %s\n",
+ error, filename);
+ return -1;
+ }
+ lseek(fd, 0, SEEK_SET);
+ filename = path;
+ block = true;
+ } else {
+ fd = open(filename, block ? O_RDONLY : (O_RDONLY | O_NONBLOCK));
+ if (fd < 0) {
+ pr_debug("Failed to open %s\n", filename);
+ return -1;
+ }
+ }
+
+ err = libbfd__read_build_id(fd, filename, bid);
+ if (err == 0)
+ goto out;
+
+ err = libelf__read_build_id(fd, filename, bid);
+ if (err == 0)
+ goto out;
+
+ err = sym_min__read_build_id(fd, filename, bid);
+out:
+ close(fd);
+ if (m.comp)
+ unlink(filename);
+ return err;
+}
+
static char *dso__find_kallsyms(struct dso *dso, struct map *map)
{
struct build_id bid = { .size = 0, };
--
2.52.0.rc2.455.g230fcf2819-goog