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| Started by | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| First post | 2015-07-20 19:20 +0200 |
| Last post | 2015-07-20 19:20 +0200 |
| Articles | 1 — 1 participant |
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Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S Josh Poimboeuf <jpoimboe@redhat.com> - 2015-07-20 19:20 +0200
| From | Josh Poimboeuf <jpoimboe@redhat.com> |
|---|---|
| Date | 2015-07-20 19:20 +0200 |
| Subject | Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S |
| Message-ID | <pOmTo-7FW-9@gated-at.bofh.it> |
On Mon, Jul 20, 2015 at 06:52:32PM +0200, Peter Zijlstra wrote: > 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? 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? 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. Agreed, though the stack dump code always prints '?' for any kernel address it finds on the stack. So there would still be a good clue. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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