Re: [PATCH bpf-next 2/3] bpf: Add size arg to build_id_parse function

Yonghong Song
2021-01-14T18:59:05Z

On 1/14/21 5:40 AM, Jiri Olsa wrote:
> It's possible to have other build id types (other than default SHA1).
> Currently there's also ld support for MD5 build id.

Currently, bpf build_id based stackmap does not returns the size of
the build_id. Did you see an issue here? I guess user space can check
the length of non-zero bits of the build id to decide what kind of
type it is, right?

>
> Adding size argument to build_id_parse function, that returns (if defined)
> size of the parsed build id, so we can recognize the build id type.
>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Song Liu <songliubraving@fb.com>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> include/linux/buildid.h | 3 ++-
> kernel/bpf/stackmap.c | 2 +-
> lib/buildid.c | 29 +++++++++++++++++++++--------
> 3 files changed, 24 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/buildid.h b/include/linux/buildid.h
> index 08028a212589..40232f90db6e 100644
> --- a/include/linux/buildid.h
> +++ b/include/linux/buildid.h
> @@ -6,6 +6,7 @@
>
> #define BUILD_ID_SIZE_MAX 20
>
> -int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id);
> +int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
> + __u32 *size);
>
> #endif
> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
> index 55d254a59f07..cabaf7db8efc 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -189,7 +189,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
>
> for (i = 0; i < trace_nr; i++) {
> vma = find_vma(current->mm, ips[i]);
> - if (!vma || build_id_parse(vma, id_offs[i].build_id)) {
> + if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) {
> /* per entry fall back to ips */
> id_offs[i].status = BPF_STACK_BUILD_ID_IP;
> id_offs[i].ip = ips[i];
> diff --git a/lib/buildid.c b/lib/buildid.c
> index 4a4f520c0e29..6156997c3895 100644
> --- a/lib/buildid.c
> +++ b/lib/buildid.c
> @@ -12,6 +12,7 @@
> */
> static inline int parse_build_id(void *page_addr,
> unsigned char *build_id,
> + __u32 *size,
> void *note_start,
> Elf32_Word note_size)
> {
> @@ -38,6 +39,8 @@ static inline int parse_build_id(void *page_addr,
> nhdr->n_descsz);
> memset(build_id + nhdr->n_descsz, 0,
> BUILD_ID_SIZE_MAX - nhdr->n_descsz);
> + if (size)
> + *size = nhdr->n_descsz;
> return 0;
> }
> new_offs = note_offs + sizeof(Elf32_Nhdr) +
> @@ -50,7 +53,8 @@ static inline int parse_build_id(void *page_addr,
> }
> …