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

[Jiri Olsa]

On Thu, Nov 26, 2020 at 06:00:03PM +0100, 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.
> 
> 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@xxxxxxxxxx>
> Cc: Song Liu <songliubraving@xxxxxx>

Alexei, Song,
could you guys please check on this one?

thanks,
jirka


> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  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
>  
> -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
>