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

[Hau Hsu <hau.hsu@sifive.com>]

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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 <mailto:hau.hsu@sifive.com>> wrote:
>>> 
>>>> On May 16, 2024, at 3:07 PM, Nelson Chu <nelson@rivosinc.com <mailto:nelson@rivosinc.com>> wrote:
>>>> 
>>>> On Thu, May 16, 2024 at 2:16 PM Hau Hsu <hau.hsu@sifive.com <mailto: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 <mailto: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
>>> 
>