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From:   Song Liu <songliubraving@fb.com>
To:     Jiri Olsa <jolsa@kernel.org>
CC:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        "Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
        Michael Petlan <mpetlan@redhat.com>,
        Ian Rogers <irogers@google.com>,
        Stephane Eranian <eranian@google.com>,
        Alexey Budankov <alexey.budankov@linux.intel.com>,
        "Andi Kleen" <ak@linux.intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCH 02/25] bpf: Add size arg to build_id_parse function
Thread-Topic: [PATCH 02/25] bpf: Add size arg to build_id_parse function
Thread-Index: AQHWxBW1sPsiV0KShkyrtdr/WYFXPKnl7QWA
Date:   Thu, 3 Dec 2020 21:23:52 +0000
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References: <20201126170026.2619053-1-jolsa@kernel.org>
 <20201126170026.2619053-3-jolsa@kernel.org>
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> On Nov 26, 2020, at 9:00 AM, Jiri Olsa <jolsa@kernel.org> wrote:
>=20
> It's possible to have other build id types (other than default SHA1).
> Currently there's also ld support for MD5 build id.
>=20
> 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.
>=20
> 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.=20

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

with one nitpick below.=20

> ---
> include/linux/buildid.h |  3 ++-
> kernel/bpf/stackmap.c   |  2 +-
> lib/buildid.c           | 29 +++++++++++++++++++++--------
> 3 files changed, 24 insertions(+), 10 deletions(-)
>=20
> 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 @@
>=20
> #define BUILD_ID_SIZE 20

Since we are handling build-id with different sizes, how about we=20
rename this as BUILD_ID_SIZE_MAX or BUILD_ID_SIZE_DEFAULT?=20

>=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);
>=20
> #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,
>=20
> 	for (i =3D 0; i < trace_nr; i++) {
> 		vma =3D 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 =3D BPF_STACK_BUILD_ID_IP;
> 			id_offs[i].ip =3D 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 =3D nhdr->n_descsz;
> 			return 0;
> 		}
> 		new_offs =3D note_offs + sizeof(Elf32_Nhdr) +
> @@ -50,7 +53,8 @@ static inline int parse_build_id(void *page_addr,
> }
>=20
> /* 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 =3D (Elf32_Ehdr *)page_addr;
> 	Elf32_Phdr *phdr;
> @@ -65,7 +69,7 @@ static int get_build_id_32(void *page_addr, unsigned ch=
ar *build_id)
>=20
> 	for (i =3D 0; i < ehdr->e_phnum; ++i) {
> 		if (phdr[i].p_type =3D=3D 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 ch=
ar *build_id)
> }
>=20
> /* 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 =3D (Elf64_Ehdr *)page_addr;
> 	Elf64_Phdr *phdr;
> @@ -89,7 +94,7 @@ static int get_build_id_64(void *page_addr, unsigned ch=
ar *build_id)
>=20
> 	for (i =3D 0; i < ehdr->e_phnum; ++i) {
> 		if (phdr[i].p_type =3D=3D 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;
> }
>=20
> -/* 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, unsign=
ed char *build_id)
> 		goto out;
>=20
> 	if (ehdr->e_ident[EI_CLASS] =3D=3D ELFCLASS32)
> -		ret =3D get_build_id_32(page_addr, build_id);
> +		ret =3D get_build_id_32(page_addr, build_id, size);
> 	else if (ehdr->e_ident[EI_CLASS] =3D=3D ELFCLASS64)
> -		ret =3D get_build_id_64(page_addr, build_id);
> +		ret =3D get_build_id_64(page_addr, build_id, size);
> out:
> 	kunmap_atomic(page_addr);
> 	put_page(page);
> --=20
> 2.26.2
>=20