Re: [PATCH 4/5] x86-64: further tighten convert-load-reloc checking

[Jan Beulich <jbeulich@suse.com>]

On 04.02.2025 11:10, H.J. Lu wrote:
> On Tue, Feb 4, 2025 at 6:04 PM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 03.02.2025 23:41, H.J. Lu wrote:
>>> On Mon, Feb 3, 2025 at 7:41 PM Jan Beulich <jbeulich@suse.com> wrote:
>>>>
>>>> REX2.M affects what insn we're actually dealing with, so we better check
>>>> this to avoid transforming (future) insns we must not touch.
>>>>
>>>> --- a/bfd/elf64-x86-64.c
>>>> +++ b/bfd/elf64-x86-64.c
>>>> @@ -2282,14 +2282,14 @@ elf_x86_64_convert_load_reloc (bfd *abfd
>>>>           if (to_reloc_pc32)
>>>>             return true;
>>>>
>>>> -         if (opcode == 0x85)
>>>> +         if (opcode == 0x85 && !(rex2 & (REX2_M << 4)))
>>>>             {
>>>>               /* Convert "test %reg, foo@GOTPCREL(%rip)" to
>>>>                  "test $foo, %reg".  */
>>>>               modrm = 0xc0 | (modrm & 0x38) >> 3;
>>>>               opcode = 0xf7;
>>>>             }
>>>> -         else if ((opcode | 0x38) == 0x3b)
>>>> +         else if ((opcode | 0x38) == 0x3b && !(rex2 & (REX2_M << 4)))
>>>>             {
>>>>               /* Convert "binop foo@GOTPCREL(%rip), %reg" to
>>>>                  "binop $foo, %reg".  */
>>>>
>>>
>>> Please add a testcase to show it makes a difference.
>>
>> Hmm, not sure how such a testcase would look like. At least some of
>> the involved opcodes have no meaning (yet) with REX2. But maybe I
>> can construct something. Still I view it as unreasonable that such
>> obvious omissions in earlier changes can't be corrected without
>> investing a lot of time in trying to make up a situation where
>> things would fail. Once again: Proof of _no failure_ should have
>> been added when these optimizations were introduced. And that proof
>> should have been extended when APX support was added. What you're
>> effectively doing is to ask me to cover for earlier omissions.
> 
> Again.  No test, no issue, no change.

Again - please adjust your attitude.

Jan