Messages in this thread | | | Date | Thu, 22 May 2014 15:22:37 -0700 | From | Cody P Schafer <> | Subject | Re: [PATCH v4 09/11] powerpc/perf: add support for the hv 24x7 interface |
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On 05/22/2014 01:19 AM, Ian Munsie wrote: > Hi Cody, > > I just tried building this with gcc 4.5, which failed with the following > warning (treated as an error): > > cc1: warnings being treated as errors > arch/powerpc/perf/hv-24x7.c: In function 'single_24x7_request': > arch/powerpc/perf/hv-24x7.c:346:1: error: the frame size of 8192 bytes is larger than 2048 bytes > make[3]: *** [arch/powerpc/perf/hv-24x7.o] Error 1 > make[2]: *** [arch/powerpc/perf] Error 2 > > My .config has CONFIG_FRAME_WARN=2048 (default on 64bit), but the > alignment constraints in this function may require 8K on the stack - > possibly a bit large? >
Yep, it is a bit large. In other places in hv-24x7 that use similar firmware interfaces (with similar alignment requirements), I've used a kmem_cache (hv_page_cache). Testing out a patch that uses that here as well.
> > Notably for some reason this warning no longer seems to trigger on gcc > 4.8 (or at least somewhere between 4.5-4.8), though the assembly does > still show it aligning the buffers.
That's a bit concerning (and might be why I didn't pick it up, using gcc 4.9.0 over here). Looking at the gcc docs, it seems to indicate that alloca() and VLAs aren't counted for -Wframe-larger-than. Perhaps gcc decided to move locally defined structures with alignment requirements into that same bucket? (while size of the structures is statically determinable, the stack consumption due to alignment is [to some degree] variable).
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