On Fri, Feb 5, 2021 at 5:42 AM Giuliano Procida <gprocida@xxxxxxxxxx> wrote:
>
> pahole -J uses libelf directly when updating a .BTF section. However,
> it uses llvm-objcopy to add .BTF sections. This commit switches to
> using libelf for both cases.
>
> This eliminates pahole's dependency on llvm-objcopy. One unfortunate
> side-effect is that vmlinux actually increases in size. It seems that
> llvm-objcopy modifies the .strtab section, discarding many strings. I
> speculate that is it discarding strings not referenced from .symtab
> and updating the references therein.
>
> Layout is left completely up to libelf and existing section offsets
> are likely to change.
>
> Signed-off-by: Giuliano Procida <gprocida@xxxxxxxxxx>
> ---
Logic looks correct. One nit below.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> libbtf.c | 127 +++++++++++++++++++++++++++++++++++--------------------
> 1 file changed, 81 insertions(+), 46 deletions(-)
>
> diff --git a/libbtf.c b/libbtf.c
> index 4ae7150..9f4abb3 100644
> --- a/libbtf.c
> +++ b/libbtf.c
> @@ -698,6 +698,7 @@ int32_t btf_elf__add_datasec_type(struct btf_elf *btfe, const char *section_name
>
> static int btf_elf__write(const char *filename, struct btf *btf)
> {
> + const char dot_BTF[] = ".BTF";
it's a constant, so more appropriate name would be DOT_BTF, but that
"dot_" notation in the name of the variable throws me off, honestly.
libbpf is using BTF_SEC_NAME for this, which IMO makes more sense as a
name for the constant
> GElf_Ehdr ehdr;
> Elf_Data *btf_data = NULL;
> Elf *elf = NULL;
> @@ -705,6 +706,7 @@ static int btf_elf__write(const char *filename, struct btf *btf)
> uint32_t raw_btf_size;
> int fd, err = -1;
> size_t strndx;
> + void *str_table = NULL;
>
> fd = open(filename, O_RDWR);
> if (fd < 0) {
[...]
