On Tue, Feb 23, 2021 at 8:38 AM Kun-Chuan Hsieh <jetswayss@xxxxxxxxx> wrote:
>
> Hi Jiri Olsa,
>
> Yes, exactly. The missing SHF_COMPRESSED value causes build failure.
>
> Compared to conditional compilation, your suggestion seems to be a better
> solution. Thank you for your suggestion. I will submit the patch v2.
>
>
> Hi Andrii Nakryiko,
>
> Yes, it is possible to detect whether libelf supports compressed ELF
> sections at compilation time. I can think of two possible methods.
> 1. Check SHF_COMPRESSED is defined. (If libelf supports compressed ELF
> sections, SHF_COMPRESSED should be defined in libelf.h or elf.h)
> 2. Check the libelf version by _ELFUTILS_PREREQ (from elfutils/version.h)
>
> Best regards,
> Kun-Chuan Hsieh
>
> On Tue, Feb 23, 2021 at 10:43 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>>
>> On Tue, Feb 23, 2021 at 01:20:01AM +0000, Kun-Chuan Hsieh wrote:
>> > Older versions of libelf cannot recognize the compressed section.
>>
>> so it's the SHF_COMPRESSED value the build fails on?
>>
>> maybe we could do just this:
>>
>> #ifndef SHF_COMPRESSED
>> #define SHF_COMPRESSED (1 << 11) /* Section with compressed data. */
>> #endif
Yeah, I was hoping it would be something like this. Or we can just
#ifdef two regions of code that rely on SHF_COMPRESSED.
>>
>> jirka
>>
>> > However, it's only required to fix the compressed section info when
>> > compiling with CONFIG_DEBUG_INFO_COMPRESSED flag is set.
>> >
>> > Only compile the compressed_section_fix function when necessary will make
>> > it easier to enable the BTF function. Since the tool resolve_btfids is
>> > compiled with host toolchain. The host toolchain might be older than the
>> > cross compile toolchain.
>> >
>> > Cc: stable@xxxxxxxxxxxxxxx
>> > Signed-off-by: Kun-Chuan Hsieh <jetswayss@xxxxxxxxx>
>> > ---
>> > tools/bpf/resolve_btfids/main.c | 4 ++++
>> > 1 file changed, 4 insertions(+)
>> >
>> > diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
>> > index 7409d7860aa6..ad40346c6631 100644
>> > --- a/tools/bpf/resolve_btfids/main.c
>> > +++ b/tools/bpf/resolve_btfids/main.c
>> > @@ -260,6 +260,7 @@ static struct btf_id *add_symbol(struct rb_root *root, char *name, size_t size)
>> > return btf_id__add(root, id, false);
>> > }
>> >
>> > +#ifdef CONFIG_DEBUG_INFO_COMPRESSED
>> > /*
>> > * The data of compressed section should be aligned to 4
>> > * (for 32bit) or 8 (for 64 bit) bytes. The binutils ld
>> > @@ -292,6 +293,7 @@ static int compressed_section_fix(Elf *elf, Elf_Scn *scn, GElf_Shdr *sh)
>> > }
>> > return 0;
>> > }
>> > +#endif
>> >
>> > static int elf_collect(struct object *obj)
>> > {
>> > @@ -370,8 +372,10 @@ static int elf_collect(struct object *obj)
>> > obj->efile.idlist_addr = sh.sh_addr;
>> > }
>> >
>> > +#ifdef CONFIG_DEBUG_INFO_COMPRESSED
>> > if (compressed_section_fix(elf, scn, &sh))
>> > return -1;
>> > +#endif
>> > }
>> >
>> > return 0;
>> > --
>> > 2.25.1
>> >
>>
