Messages in this thread | | | Date | Fri, 16 Dec 2011 01:23:32 -0800 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH] x86: Use -m-omit-leaf-frame-pointer to shrink text size |
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On 12/16/2011 12:53 AM, Ingo Molnar wrote: > * Ingo Molnar <mingo@elte.hu> wrote: > >> [...] >> >> The call-chains are still intact for quality backtraces and >> for call-chain profiling (perf record -g), as the backtrace >> walker can deduct the full backtrace from the RIP of a leaf >> function and the parent chain. > Hm, noticed one complication while looking at annotated assembly > code in perf top. Code doing function calls from within asm() is > incorrectly marked 'leaf' by GCC: > > ffffffff812b82d8 <arch_local_save_flags>: > ffffffff812b82d8: ff 14 25 00 d9 c1 81 callq *0xffffffff81c1d900 > ffffffff812b82df: c3 retq > > So all the paravirt details will have to be fixed, so that GCC > is able to see that there's a real function call done inside. > Jeremy, Konrad?
Um. So the issue is that a function that contains only pvops looks like it's a leaf to gcc and it does some leaf-function optimisation?
How can we tell gcc the asm contains a call, or otherwise suppress the "leaf function" classification?
The alternative is to just make it a plain C-level indirect call, but then we'd lose all the patching and callee-save optimisations.
Any suggestions?
Thanks, J
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