Re: [PATCH 1/1] perf tools: Fix Symbol Address for ET_DYN

[Tong Shen <endlessroad@google.com>]

In my case it's not a prelink-ed dso; but I believe the effect is the same.

Specifically:
- Program headers and section headers contain absolute address;
- Symbol addresses are also absolute;
- There's no relocation in my case.

On Thu, Sep 25, 2014 at 10:45 PM, Namhyung Kim <namhyung@kernel.org> wrote:
> Hi Tong,
>
> Does a non-relocatable-dyn mean a prelink-ed dso?
>
> Thanks,
> Namhyung
>
>
> On Wed, 24 Sep 2014 17:28:24 -0700, Tong Shen wrote:
>> Gentle Ping :-)
>>
>> On Mon, Sep 15, 2014 at 11:06 AM, Tong Shen <endlessroad@google.com> wrote:
>>> Gentle ping :-)
>>>
>>> On Thu, Sep 11, 2014 at 1:38 PM, Arnaldo Carvalho de Melo
>>> <acme@kernel.org> wrote:
>>>> Em Thu, Sep 11, 2014 at 11:21:40AM -0700, Tong Shen escreveu:
>>>>> Hi Arnaldo,
>>>>>
>>>>> Thanks a lot for the comment!
>>>>>
>>>>> I fixed the coding style and added a helper function with comments, as
>>>>> you suggested :-)
>>>>> See attachment.
>>>>
>>>> That is much better, I'm adding lkml to the CC list so that we can give
>>>> other people the opportunity to chime in.
>>>>
>>>> - Arnaldo
>>>>
>>>>> On Thu, Sep 11, 2014 at 8:01 AM, Arnaldo Carvalho de Melo
>>>>> <acme@kernel.org> wrote:
>>>>> > Em Fri, Sep 05, 2014 at 11:38:02AM -0700, Tong Shen escreveu:
>>>>> >> Hi linux-perf-users,
>>>>> >>
>>>>> >> It's actually a patch, and I didn't find a development mailing list
>>>>> >> for perf, so I just post it here. If this is not the right place to
>>>>> >
>>>>> > You can post it here, but please add the maintainers to the CC list, so
>>>>> > that we can more quickly see your message.
>>>>> >
>>>>> > Comments below:
>>>>> >
>>>>> >> post patches, could someone direct me to it? Thanks in advance!
>>>>> >>
>>>>> >> In tools/perf/util/symbol-elf.c, we don't adjust symbol address for
>>>>> >> ET_DYN type of ELF files because we think ET_DYN is always
>>>>> >> relocatable.
>>>>> >>
>>>>> >> But that's not necessarily true; there are some non-relocatable ET_DYN
>>>>> >> ELF files. For those files, we should still adjust symbol address.
>>>>> >
>>>>> >> Suggested patch: (HTML subpart now allowed in this mailing list...)
>>>>> >
>>>>> >> +++ b/perf-3.12.0/tools/perf/util/symbol-elf.c
>>>>> >> @@ -915,7 +915,10 @@ int dso__load_sym(struct dso *dso, struct map *map,
>>>>> >
>>>>> >>               if ((used_opd && runtime_ss->adjust_symbols)
>>>>> >> -                             || (!used_opd && syms_ss->adjust_symbols)) {
>>>>> >> +                             || (!used_opd && syms_ss->adjust_symbols)
>>>>> >> +                             || (syms_ss->ehdr.e_type == et_dyn
>>>>> >> +                                     && shdr.sh_addr != shdr.sh_offset
>>>>> >> +                                     && elf_sec__is_text(&shdr, secstrs))) {
>>>>> >
>>>>> > Please try to follow kernel coding style in these tools, i.e. the &&
>>>>> > should be at the end, the expression on each line should be aligned just
>>>>> > after the opening parens.
>>>>> >
>>>>> > If, like in this case, you find something not following that style, take
>>>>> > the opportunity to fix it :-)
>>>>> >
>>>>> > But back to your change, I'll have to look at this code further, just
>>>>> > looking at the excerpt above I find it way too confusing, and your patch
>>>>> > makes it even more so...
>>>>> >
>>>>> > Can you introduce some suitably named helper that has those extra
>>>>> > conditions you're adding now and then add it to this conditional?
>>>>> >
>>>>> > I.e. make it somethine like:
>>>>> >
>>>>> > -               if ((used_opd && runtime_ss->adjust_symbols)
>>>>> > -                               || (!used_opd && syms_ss->adjust_symbols)) {
>>>>> > +               if ((used_opd && runtime_ss->adjust_symbols) ||
>>>>> > +                   (!used_opd && syms_ss->adjust_symbols)   ||
>>>>> > +                   syms__some_suitable_name(syms_ss, &shdr)) {
>>>>> >
>>>>> > And then add your explanation of these kinds of files as a comment over
>>>>> > this new function, please?
>>>>> >
>>>>> >>                       pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " "
>>>>> >>                                 "sh_addr: %#" PRIx64 " sh_offset: %#" PRIx64 "\n", __func__,
>>>>> >>                                 (u64)sym.st_value, (u64)shdr.sh_addr,
>>>>> >
>>>>> > Best regards,
>>>>> >
>>>>> > - Arnaldo
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Best Regards, Tong Shen
>>>>
>>>>> diff --git a/perf-3.12.0/tools/perf/util/symbol-elf.c b/perf-3.12.0/tools/perf/util/symbol-elf.c
>>>>> index a9c829b..f9bd488 100644
>>>>> --- a/perf-3.12.0/tools/perf/util/symbol-elf.c
>>>>> +++ b/perf-3.12.0/tools/perf/util/symbol-elf.c
>>>>> @@ -673,6 +673,27 @@ static u64 ref_reloc(struct kmap *kmap)
>>>>>       return 0;
>>>>>  }
>>>>>
>>>>> +/**
>>>>> + * is_non_relocatable_dyn - check if ELF file is ET_DYN, but not relocatable
>>>>> + * @ehdr: ELF header of the ELF file
>>>>> + * @shdr: a section header in the ELF file
>>>>> + *
>>>>> + * For ELF files with type ET_EXEC and ET_REL, we adjust symbol addresses in
>>>>> + * symbol table in dso__load_sym() so that later we can always locate symbols
>>>>> + * by sym.st_value + map_address_of_ELF_file.
>>>>> + *
>>>>> + * But ELF files with type ET_DYN may need adjusting as well, if they are
>>>>> + * not relocatable. There's no standard way to tell if an ELF file with type
>>>>> + * ET_DYN is relocatable. One possible way to do that is checking if
>>>>> + * sh_addr == sh_offset for .text section.
>>>>> + */
>>>>> +static bool is_non_relocatable_dyn(GElf_Ehdr *ehdr, GElf_Shdr *shdr,
>>>>> +                                   Elf_Data *secstrs) {
>>>>> +     return ehdr->e_type == ET_DYN &&
>>>>> +            elf_sec__is_text(shdr, secstrs) &&
>>>>> +            shdr->sh_offset != shdr->sh_addr;
>>>>> +}
>>>>> +
>>>>>  int dso__load_sym(struct dso *dso, struct map *map,
>>>>>                 struct symsrc *syms_ss, struct symsrc *runtime_ss,
>>>>>                 symbol_filter_t filter, int kmodule)
>>>>> @@ -914,8 +935,9 @@ int dso__load_sym(struct dso *dso, struct map *map,
>>>>>                       goto new_symbol;
>>>>>               }
>>>>>
>>>>> -             if ((used_opd && runtime_ss->adjust_symbols)
>>>>> -                             || (!used_opd && syms_ss->adjust_symbols)) {
>>>>> +             if ((used_opd && runtime_ss->adjust_symbols) ||
>>>>> +                 (!used_opd && syms_ss->adjust_symbols) ||
>>>>> +                 is_non_relocatable_dyn(&ehdr, &shdr, secstrs)) {
>>>>>                       pr_debug4("%s: adjusting symbol: st_value: %#" PRIx64 " "
>>>>>                                 "sh_addr: %#" PRIx64 " sh_offset: %#" PRIx64 "\n", __func__,
>>>>>                                 (u64)sym.st_value, (u64)shdr.sh_addr,
>>>>
>>>
>>>
>>>
>>> --
>>> Best Regards, Tong Shen



-- 
Best Regards, Tong Shen