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@redhat.com
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.
Thanks everyone, Daniel