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Date: Mon, 20 Jul 2015 18:52:32 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Josh Poimboeuf <jpoimboe@...hat.com> Cc: Andy Lutomirski <luto@...capital.net>, Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Linus Torvalds <torvalds@...ux-foundation.org>, Andi Kleen <andi@...stfloor.org>, Pedro Alves <palves@...hat.com>, X86 ML <x86@...nel.org>, live-patching@...r.kernel.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S On Mon, Jul 20, 2015 at 11:36:46AM -0500, Josh Poimboeuf wrote: > If a function doesn't call any other functions, then it won't ever show > up in a stack trace unless: > > a) the function itself walks the stack, in which case the frame pointer > isn't necessary; or > > b) The function gets hit by an interrupt/exception, in which case frame > pointers can't be 100% relied upon anyway. In case the interrupt happens whilst setting up the frame, right? > I've noticed that gcc *does* seem to create stack frames for leaf > functions. But it's inconsistent, because the early exit path of some > functions will skip the stack frame creation and go straight to the > return. > > We could probably get a good performance boost with the > -momit-leaf-frame-pointer flag. Though it would make stack traces less > reliable when a leaf function gets interrupted. So the information we'd loose in that case would be the location in the calling function, right? Which isn't a problem, if the current function (as obtained through RIP) is only ever called once. However if there's multiple call sites this might be a wee bit confusing. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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