Re: [PATCH 02/25] bpf: Add size arg to build_id_parse function

Song Liu
2020-12-03T21:24:51Z

> On Nov 26, 2020, at 9:00 AM, Jiri Olsa <jolsa@kernel.org> wrote:
>
> It's possible to have other build id types (other than default SHA1).
> Currently there's also ld support for MD5 build id.
>
> 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>

Sorry for the late response. The patch looks good to me.

Acked-by: Song Liu <songliubraving@fb.com>

with one nitpick below.

> ---
> 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 3be5b49719f1..72639d433873 100644
> --- a/include/linux/buildid.h
> +++ b/include/linux/buildid.h
> @@ -6,6 +6,7 @@
>
> #define BUILD_ID_SIZE 20

Since we are handling build-id with different sizes, how about we
rename this as BUILD_ID_SIZE_MAX or BUILD_ID_SIZE_DEFAULT?

>
> -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 7df08f8af5a1..a05fac2cbb05 100644
> --- a/kernel/bpf/stackmap.c
> +++ b/kernel/bpf/stackmap.c
> @@ -199,7 +199,7 @@ 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 e8d5feb7ef20..dbe1b7e247f3 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 - 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,
> }
>
> /* Parse build ID from 32-bit ELF */
> -static int get_build_id_32(void *page_addr, unsigned char *build_id)
> +static int get_build_id_32(void *page_addr, unsigned char *build_id,
> + __u32 *size)
> {
> Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
> Elf32_Phdr *phdr;
> @@ -65,7 +69,7 @@ static int get_build_id_32(void *page_addr, unsigned char *build_id)
>
> for (i = 0; i < ehdr->e_phnum; ++i) {
> if (phdr[i].p_type == PT_NOTE &&
> - !parse_build_id(page_addr, build_id,
> + !parse_build_id(page_addr, build_id, size,
> page_addr + phdr[i].p_offset,
> phdr[i].p_filesz))
> return 0;
> @@ -74,7 +78,8 @@ static int get_build_id_32(void *page_addr, unsigned char *build_id)
> }
>
> /* Parse build ID from 64-bit ELF */
> -static int get_build_id_64(void *page_addr, unsigned char *build_id)
> +static int get_build_id_64(void *page_addr, unsigned char *build_id,
> + __u32 *size)
> {
> Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
> Elf64_Phdr *phdr;
> @@ -89,7 +94,7 @@ static int get_build_id_64(void *page_addr, unsigned char *build_id)
>
> for (i = 0; i < ehdr->e_phnum; ++i) {
> if (phdr[i].p_type == PT_NOTE &&
> - !parse_build_id(page_addr, build_id,
> + !parse_build_id(page_addr, build_id, size,
> page_addr + phdr[i].p_offset,
> phdr[i].p_filesz))
> return 0;
> @@ -97,8 +102,16 @@ static int get_build_id_64(void *page_addr, unsigned char *build_id)
> return -EINVAL;
> }
>
> -/* Parse build ID of ELF file mapped to vma */
> -int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id)
> +/*
> + * Parse build ID of ELF file mapped to vma
> + * @vma: vma object
> + * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
> + * @size: returns actual build id size in case of success
> + *
> + * Returns 0 on success, otherwise error (< 0).
> + */
> +int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
> + __u32 *size)
> {
> Elf32_Ehdr *ehdr;
> struct page *page;
> @@ -126,9 +139,9 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id)
> goto out;
>
> if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
> - ret = get_build_id_32(page_addr, build_id);
> + ret = get_build_id_32(page_addr, build_id, size);
> else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
> - ret = get_build_id_64(page_addr, build_id);
> + ret = get_build_id_64(page_addr, build_id, size);
> out:
> kunmap_atomic(page_addr);
> put_page(page);
> --
> 2.26.2
>