[PATCH] i386: Issue an error for baseless @GOT relocation with relaxation

[Jan Beulich]

On 27.10.2025 11:09, H.J. Lu wrote:
> On Mon, Oct 27, 2025 at 5:52 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 27.10.2025 10:31, H.J. Lu wrote:
>>> On Mon, Oct 27, 2025 at 4:41 PM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> On 26.10.2025 00:28, H.J. Lu wrote:
>>>>> When -mrelax-relocations=no is used, don't generate baseless R_386_GOT32X
>>>>> relocation.  Issue an error instead.
>>>>>
>>>>> PR gas/33552
>>>>> * config/tc-i386.c (output_disp): Issue an error for baseless @GOT
>>>>> relocation without relaxation in 32-bit.
>>>>> * testsuite/gas/i386/got-no-relax-error.l: New file.
>>>>> * testsuite/gas/i386/got-no-relax-error.s: Likewise.
>>>>> * testsuite/gas/i386/got-no-relax.d: Don't use got.s.  Remove
>>>>> R_386_GOT32X entries.
>>>>> * testsuite/gas/i386/i386.exp: Run got-no-relax-error.
>>>>>
>>>>
>>>> Please can you add a reference to the part of the spec that puts in place
>>>> this restriction?
>>>
>>> It is more of an ISA restriction.  In i386 psABI, there are 2 kinds of PLTs,
>>> one with EBX for PIC and the other without EBX for non-PIC.  The baseless
>>> @GOT reloc can only be used with non-PIC PLT.
>>
>> But the two PLT kinds must be specified somewhere. As must be the relocation
> 
> It is in i386 psABI.   They are implemented in elf32-i386.c.
> 
>> types. Furthermore, how does the PLT come into play here when we're talking
>> of a GOT reloc? R_386-GOT32X is G + A - GOT / G + A, i.e. nothing PLT-ish in
> 
> jmp *foo@GOT
> 
> was added for -fno-plt.  For the same reason as non-PIC PLT, it only works
> without PIC.
> 
>> there. The description in the psABI also clearly mentions forms with and
>> without base register.
> 
> It is covered in:
> 
> https://gitlab.com/x86-psABIs/i386-ABI

Hmm, yes, I see the text there was extended at some point. Having a single
reloc with two different calculations is, however, a no-go. Even more so with
an arch like x86, where you can't reliably move backwards in the instruction
byte stream.

Jan