Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers
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- Subject: Re: [tip: x86/asm] x86/asm: Make ASM_CALL_CONSTRAINT conditional on frame pointers
- From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
- Date: Mon, 3 Mar 2025 14:47:58 -0800
- Cc: linux-kernel@xxxxxxxxxxxxxxx, tip-bot2 for Josh Poimboeuf <tip-bot2@xxxxxxxxxxxxx>, linux-tip-commits@xxxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, x86@xxxxxxxxxx
- In-reply-to: <20250303224548.pghzo2j4hdww7nxt@jpoimboe>
- References: <174099976188.10177.7153571701278544000.tip-bot2@tip-bot2> <C77024F6-3087-40A3-8AFB-A642EECAFF4E@zytor.com> <20250303224548.pghzo2j4hdww7nxt@jpoimboe>
On Mon, Mar 03, 2025 at 02:45:50PM -0800, Josh Poimboeuf wrote:
> On Mon, Mar 03, 2025 at 02:31:50PM -0800, H. Peter Anvin wrote:
> > >+#ifdef CONFIG_UNWINDER_FRAME_POINTER
> > > #define ASM_CALL_CONSTRAINT "r" (__builtin_frame_address(0))
> > >+#else
> > >+#define ASM_CALL_CONSTRAINT
> > >+#endif
> > >
> > > #endif /* __ASSEMBLY__ */
> > >
> >
> > Wait, why was this changed? I actually tested this form at least once
> > and found that it didn't work under all circumstances...
>
> Do you have any more details about where this didn't work? I tested
> with several configs and it seems to work fine. Objtool will complain
> if it doesn't work.
>
> See here for the justification (the previous version was producing crap
> code in Clang):
Gah, that link doesn't work because I forgot to cc lkml.
Here's the tip bot link:
https://lore.kernel.org/all/174099976253.10177.12542657892256193630.tip-bot2@tip-bot2/
--
Josh
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