* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 3 Mar 2025 at 01:02, tip-bot2 for Josh Poimboeuf > <tip-bot2@xxxxxxxxxxxxx> wrote: > > > > x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers > > > > With frame pointers enabled, ASM_CALL_CONSTRAINT is used in an inline > > asm statement with a call instruction to force the compiler to set up > > the frame pointer before doing the call. > > > > Without frame pointers, no such constraint is needed. Make it > > conditional on frame pointers. > > Can we please explain *why* this is done? > > It may not be required, but it makes the source code uglier and adds a > conditional. What's the advantage of adding this extra logic? > > I'm sure there is some reason for this change, but that reason should > be explained. > > Because "we don't need it" cuts both ways. Maybe we don't need the > ASM_CALL_CONSTRAINT, but it also didn't use to hurt us. > > The problems seems entirely caused by the change to use a strictly > inferior version of ASM_CALL_CONSTRAINT. > > Is there really no better option? Because the new ASM_CALL_CONSTRAINT > seems actively horrendous. So Josh forgot to Cc: lkml in this 5-patch series: 63852 Mar 02 Josh Poimboeuf | [PATCH 0/5] x86: Fix ASM_CALL_CONSTRAINT for Clang 19 and disable it for ORC 63853 Mar 02 Josh Poimboeuf | ├─>[PATCH 1/5] KVM: VMX: Use named operands in inline asm 63855 Mar 02 Josh Poimboeuf | ├─>[PATCH 2/5] x86/hyperv: Use named operands in inline asm 63856 Mar 02 Josh Poimboeuf | ├─>[PATCH 3/5] x86/alternative: Simplify alternative_call() interface 63857 Mar 02 Josh Poimboeuf | ├─>[PATCH 4/5] x86: Fix ASM_CALL_CONSTRAINT for Clang 19 + KCOV + KMSAN 63858 Mar 02 Josh Poimboeuf | ├─>[PATCH 5/5] x86: Make ASM_CALL_CONSTRAINT conditional on frame pointers ... which omission I tried to fix in the commits by adding Cc: lkml - but which made the discussion unthreaded on Lore ... a mistake I won't repeat. This reply of yours is for patch 5/5 which is arguably out of context in isolation, while the main justification for changing ASM_CALL_CONSTRAINT is in 4/5 (a Clang 19 code generation quirk to fix a warning) - see attached it below. The full 5-patch series in -next is: cccc85ea4032 KVM: VMX: Use named operands in inline asm 2668d7b4aff8 x86/hyperv: Use named operands in inline asm 1edd623ccaaf x86/alternatives: Simplify alternative_call() interface 96092b7552d9 x86/asm: Fix ASM_CALL_CONSTRAINT for Clang 19 + KCOV + KMSAN e5ff90b179d4 x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers I bounced you the key emails, but I'm not sure that helps much. I'll avoid this situation in the future, Cc:lkml works well for individual patches and I used it in the past, but it loses context in the series-submission case. Thanks, Ingo ===============================>
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