On Thu, 17 Jun 2021 at 04:22, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote: > > On 6/17/21 11:02 AM, Jiri Olsa wrote: > > On Thu, Jun 17, 2021 at 12:28:00AM +0200, Mark Wielaard wrote: > >> On Wed, Jun 16, 2021 at 06:38:33PM +0200, Jiri Olsa wrote: > >>>>> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c > >>>>> index d636643ddd35..f32c059fbfb4 100644 > >>>>> --- a/tools/bpf/resolve_btfids/main.c > >>>>> +++ b/tools/bpf/resolve_btfids/main.c > >>>>> @@ -649,6 +649,9 @@ static int symbols_patch(struct object *obj) > >>>>> if (sets_patch(obj)) > >>>>> return -1; > >>>>> + /* Set type to ensure endian translation occurs. */ > >>>>> + obj->efile.idlist->d_type = ELF_T_WORD; > >>>> > >>>> The change makes sense to me as .BTF_ids contains just a list of > >>>> u32's. > >>>> > >>>> Jiri, could you double check on this? > >>> > >>> the comment in ELF_T_WORD declaration suggests the size depends on > >>> elf's class? > >>> > >>> ELF_T_WORD, /* Elf32_Word, Elf64_Word, ... */ > >>> > >>> data in .BTF_ids section are allways u32 > >>> > >>> I have no idea how is this handled in libelf (perhaps it's ok), > >>> but just that comment above suggests it could be also 64 bits, > >>> cc-ing Frank and Mark for more insight > >> > >> It is correct to use ELF_T_WORD, which means a 32bit unsigned word. > >> > >> The comment is meant to explain that, but is really confusing if you > >> don't know that Elf32_Word and Elf64_Word are the same thing (a 32bit > >> unsigned word). This comes from being "too consistent" in defining all > >> data types for both 32bit and 64bit ELF, even if those types are the > >> same in both formats... > >> > >> Only Elf32_Addr/Elf64_Addr and Elf32_Off/Elf64_Off are different > >> sizes. But Elf32/Elf_64_Half (16 bit), Elf32/Elf64_Word (32 bit), > >> Elf32/Elf64_Xword (64 bit) and their Sword/Sxword (signed) variants > >> are all identical data types in both the Elf32 and Elf64 formats. > >> > >> I don't really know why. It seems the original ELF spec was 32bit only > >> and when introducing the ELF64 format "they" simply duplicated all > >> data types whether or not those data type were actually different > >> between the 32 and 64 bit format. > > > > nice, thanks for details > > > > Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > Tony, could you do a v2 and summarize the remainder of the discussion in > here for the commit message? Would be good to explicitly document the > assumptions made and why they work. Sure, Daniel, I'll update the commit details and resend. Thanks, Tony > Thanks everyone, > Daniel
