Messages in this thread | | | Subject | Re: [PATCH bpf-next 2/3] bpf: Add size arg to build_id_parse function | From | Yonghong Song <> | Date | Thu, 14 Jan 2021 13:05:33 -0800 |
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On 1/14/21 12:01 PM, Jiri Olsa wrote: > On Thu, Jan 14, 2021 at 10:56:33AM -0800, Yonghong Song wrote: >> >> >> 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? > > you can have zero bytes in the build id hash, so you need to get the size > > I never saw MD5 being used in practise just SHA1, but we added the > size to be complete and make sure we'll fit with build id, because > there's only limited space in mmap2 event
I am asking to check whether we should extend uapi struct bpf_stack_build_id to include build_id_size as well. I guess we can delay this until a real use case.
> > jirka > >> >>> >>> 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, >>> } >> [...] >> >
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