Re: [PATCH 2/2] riscv: Fix R_RISCV_IRELATIVE overwrite and order issues

[Nelson Chu <nelson@rivosinc.com>]

[-- Attachment #1: Type: text/plain, Size: 6939 bytes --]

Your code will break what we discussed in the pr13302 - "riscv inserts the
dynamic relocations in the order of plt and got entry offset"

On Thu, May 23, 2024 at 11:54 AM Hau Hsu <hau.hsu@sifive.com> wrote:

> I used riscv-gnu-toolchain to run gcc test suite (linux) and got no
> regressions:
>
>                ========= Summary of gcc testsuite =========
>                             | # of unexpected case / # of unique
> unexpected case
>                             |          gcc |          g++ |     gfortran |
>  rv64imafdc/  lp64d/ medlow |    0 /     0 |    0 /     0 |    0 /     0 |
>
>
> I think the quite easy solution is - don't use riscv_elf_append_rela to
> emit dynamic IRELATIVE for R_RISCV_32/64 into iplt section.  Seems like
> commit 51a8a7c2e3cc only handles the finish_dynamic_symbol, but forgot to
> apply a similar fix in the relocate_section.
>
>
> It seems my change works. But I can try to modify code as suggested.
>
>
> Hau Hsu
>
>
>
>
> On May 17, 2024, at 10:32 AM, Hau Hsu <hau.hsu@sifive.com> wrote:
>
> Let me run more toolchain integrated tests.
> Thanks!
>
> Hau
>
>
>
> On May 16, 2024, at 4:28 PM, Nelson Chu <nelson@rivosinc.com> wrote:
>
> I think the quite easy solution is - don't use riscv_elf_append_rela to
> emit dynamic IRELATIVE for R_RISCV_32/64 into iplt section.  Seems like
> commit 51a8a7c2e3cc only handles the finish_dynamic_symbol, but forgot to
> apply a similar fix in the relocate_section.
>
> https://github.com/bminor/binutils-gdb/blob/master/bfd/elfnn-riscv.c#L2408
> diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
> index 604f6de4511..dca446c0495 100644
> --- a/bfd/elfnn-riscv.c
> +++ b/bfd/elfnn-riscv.c
> @@ -2399,13 +2399,16 @@ riscv_elf_relocate_section (bfd *output_bfd,
>                        2. .rela.got section in dynamic executable.
>                        3. .rela.iplt section in static executable.  */
>                     if (bfd_link_pic (info))
> -                     sreloc = htab->elf.irelifunc;
> +                     riscv_elf_append_rela (output_bfd,
> htab->elf.irelifunc, &outrel);
>                     else if (htab->elf.splt != NULL)
> -                     sreloc = htab->elf.srelgot;
> +                     riscv_elf_append_rela (output_bfd,
> htab->elf.srelgot, &outrel);
>                     else
> -                     sreloc = htab->elf.irelplt;
> -
> -                   riscv_elf_append_rela (output_bfd, sreloc, &outrel);
> +                     {
> +                       const struct elf_backend_data *bed =
> get_elf_backend_data (output_bfd);
> +                       bfd_vma iplt_idx = htab->last_iplt_index--;
> +                       bfd_byte *loc = htab->elf.irelplt->contents +
> iplt_idx * sizeof (ElfNN_External_Rela);
> +                       bed->s->swap_reloca_out (output_bfd, &outrel, loc);
> +                     }
>
>                     /* If this reloc is against an external symbol, we
>                        do not want to fiddle with the addend.  Otherwise,
>
> The above changes seem to fix the testcase you provided, but without
> testing fully riscv-gnu-toolchain regressions.
> Or we should find a way to handle reloc_index for iplt, and all use
> riscv_elf_append_rela to emit the dynamic relocation.
>
> Nelson
>
> On Thu, May 16, 2024 at 3:30 PM Hau Hsu <hau.hsu@sifive.com> wrote:
>
>>
>> On May 16, 2024, at 3:07 PM, Nelson Chu <nelson@rivosinc.com> wrote:
>>
>> On Thu, May 16, 2024 at 2:16 PM Hau Hsu <hau.hsu@sifive.com> wrote:
>>
>>> Hi Nelson,
>>>
>>> Sorry for the late reply.
>>>
>>> On May 8, 2024, at 9:00 AM, Nelson Chu <nelson@rivosinc.com> wrote:
>>>
>>> Can you provide the testcase to show the case which I mentioned in the
>>> pr13302?  Which is that an ifunc with a dynamic jump slot calls another
>>> ifunc, and are not in the rel.dyn.
>>>
>>> I am not quite sure what's the issue you mentioned in PR13302.
>>> You mean the order issue of cause by one ifunc (generates
>>> JUMP_SLOT[32|64]) calls another JUMP_SLOT[32|64] ifunc?
>>>
>>> Since according to the testcase below, it seems no requirement to apply
>>> this fix though.
>>>
>>> The new test case uses two methods to call ifuncs:
>>> 1. Through a normal function call: PLT + GOT
>>> 2. Through a global function pointer: GOT only
>>>
>>> Without the fix, the relocation of the first method overwrites the
>>> second's.
>>> The relocation section of my test case would be:
>>>
>>> Relocation section '.rela.plt' at offset 0x94 contains 2 entries:
>>>  Offset     Info    Type                Sym. Value  Symbol's Name +
>>> Addend
>>> 000110dc  0000003a R_RISCV_IRELATIVE                 100c0
>>> 00000000  00000000 R_RISCV_NONE                      0
>>>
>>>
>>> With the fix, it becomes
>>>
>>> Relocation section '.rela.plt' at offset 0x94 contains 2 entries:
>>>  Offset     Info    Type                Sym. Value  Symbol's Name +
>>> Addend
>>> 000110e0  0000003a R_RISCV_IRELATIVE                 100c0
>>> 000110dc  0000003a R_RISCV_IRELATIVE                 100c0
>>>
>>>
>> So it seems like the overwrite problem, not the order problem we were
>> discussing in the pr13302...
>>
>>
>> Yes. Sorry that I didn't explain the whole story well.
>>
>> This PR is originally to fix the overwrite problem, as my commit message
>> says:
>> > This commit resolved two issues:
>> > 1. When an ifunc is referenced by a pointer, the relocation of
>> >   the pointer in .rela.plt would be overwritten by normal ifunc call.
>> We found the issue when building glibc testbench statically.
>>
>> To fix this issue, I sent a PR (
>> https://sourceware.org/pipermail/binutils/2023-July/128485.html) about a
>> year ago.
>> The PR use the method smilier to your previous commit, i.e.
>>
>> https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=51a8a7c2e3cc0730831963651a55d23d1fae624d
>> Then you suggested to check whether the relocation order is correct.
>> After that I checked the X86 implementation, I sent this PR.
>>
>>
>>
>>> --- /dev/null
>>>> +++ b/ld/testsuite/ld-riscv-elf/ifunc-macro.s
>>>> @@ -0,0 +1,19 @@
>>>> +/* Define macros to handle similar behaviors for rv32/rv64.
>>>> +   Assumes macro "__64_bit__" defined for rv64.
>>>> +   The macro is specifically defined for ifunc tests in
>>>> ld-riscv-elf.exp. */
>>>> +
>>>> +.macro PTR_DATA name
>>>> +.ifdef __64_bit__
>>>> +       .quad   \name
>>>> +.else
>>>> +       .long   \name
>>>> +.endif
>>>> +.endm
>>>> +
>>>> +.macro LOAD rd, rs, offset
>>>> +.ifdef __64_bit__
>>>> +       ld      \rd, \offset (\rs)
>>>> +.else
>>>> +       lw      \rd, \offset (\rs)
>>>> +.endif
>>>> +.endm
>>>
>>>
>> Btw, can we not use these macroes?
>>
>>
>> No problem. I just want to avoid similar codes in the ifunc tests.
>>
>>
>> Nelson
>>
>>
>>
>
>