[PATCH RFC v2 bpf-next 5/9] selftests/bpf: Add read_buildid function

Jiri Olsa
2023-02-28T09:33:36Z

Adding read_build_id function that parses out build id from
specified binary.

It will replace extract_build_id and also be used in following
changes.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/testing/selftests/bpf/trace_helpers.c | 98 +++++++++++++++++++++
tools/testing/selftests/bpf/trace_helpers.h | 5 ++
2 files changed, 103 insertions(+)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
index 09a16a77bae4..c10e16626cd3 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/tools/testing/selftests/bpf/trace_helpers.c
@@ -11,6 +11,9 @@
#include <linux/perf_event.h>
#include <sys/mman.h>
#include "trace_helpers.h"
+#include <linux/limits.h>
+#include <libelf.h>
+#include <gelf.h>

#define DEBUGFS "/sys/kernel/debug/tracing/"

@@ -230,3 +233,98 @@ ssize_t get_rel_offset(uintptr_t addr)
fclose(f);
return -EINVAL;
}
+
+static int
+parse_build_id_buf(const void *note_start, Elf32_Word note_size,
+ char *build_id)
+{
+ Elf32_Word note_offs = 0, new_offs;
+
+ while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
+ Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
+
+ if (nhdr->n_type == 3 &&
+ nhdr->n_namesz == sizeof("GNU") &&
+ !strcmp((char *)(nhdr + 1), "GNU") &&
+ nhdr->n_descsz > 0 &&
+ nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
+ memcpy(build_id, note_start + note_offs +
+ ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
+ nhdr->n_descsz);
+ memset(build_id + nhdr->n_descsz, 0,
+ BPF_BUILD_ID_SIZE - nhdr->n_descsz);
+ return (int) nhdr->n_descsz;
+ }
+
+ new_offs = note_offs + sizeof(Elf32_Nhdr) +
+ ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
+
+ if (new_offs >= note_size)
+ break;
+ note_offs = new_offs;
+ }
+
+ return -EINVAL;
+}
+
+/* Reads binary from *path* file and returns it in the *build_id*
+ * which is expected to be at least BPF_BUILD_ID_SIZE bytes.
+ * Returns size of build id on success. On error the error value
+ * is returned.
+ */
+int read_build_id(const char *path, char *build_id)
+{
+ int fd, err = -EINVAL;
+ Elf *elf = NULL;
+ GElf_Ehdr ehdr;
+ size_t max, i;
+
+ fd = open(path, O_RDONLY | O_CLOEXEC);
+ if (fd < 0)
+ return -errno;
+
+ (void)elf_version(EV_CURRENT);
+
+ elf = elf_begin(fd, ELF_C_READ, NULL);
+ if (!elf)
+ goto out;
+
+ if (elf_kind(elf) != ELF_K_ELF)
+ goto out;
+
+ if (gelf_getehdr(elf, &ehdr) == NULL)
+ goto out;
+
+ if (ehdr.e_ident[EI_CLASS] != ELFCLASS64)
+ goto out;
+
+ for (i = 0; i < ehdr.e_phnum; i++) {
+ GElf_Phdr mem, *phdr;
+ char *data;
+
+ phdr = gelf_getphdr(elf, i, &mem);
+ if (!phdr)
+ goto out;
+
+ if (phdr->p_type != PT_NOTE)
+ continue;
+
+ data = elf_rawfile(elf, &max);
+ if (!data)
+ goto out;
+
+ if (phdr->p_offset >= max ||
+ (phdr->p_offset + phdr->p_memsz >= max))
+ goto out;
+
+ err = parse_build_id_buf(data + phdr->p_offset, phdr->p_memsz, build_id);
+ if (err > 0)
+ goto out;
+ }
+
+out:
+ if (elf)
+ elf_end(elf);
+ close(fd);
+ return err;
+}
diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
index 53efde0e2998..50b2cc498ba7 100644
--- a/tools/testing/selftests/bpf/trace_helpers.h
+++ b/tools/testing/selftests/bpf/trace_helpers.h
@@ -4,6 +4,9 @@

#include <bpf/libbpf.h>

+#define ALIGN(x, a) __ALIGN_MASK(x, (typeof(x))(a)-1)
+#define __ALIGN_MASK(x, mask) (((x)+(mask))&~(mask))
+
struct ksym {
long addr;
char *name;
@@ -23,4 +26,6 @@ void read_trace_pipe(void);
ssize_t get_uprobe_offset(const void *addr);
ssize_t get_rel_offset(uintptr_t addr);

+int read_build_id(const char *path, char *build_id);
+
#endif
--
2.39.2