On Mon, 8 Feb 2021 at 22:29, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> 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
>
Ack. Changed. I'll wait a day for further comments before reposting.
Thanks again,
Giuliano.
>
> > 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) {
>
> [...]
