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

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

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> 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 <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