Messages in this thread | | | Date | Wed, 4 Nov 2015 16:04:57 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH 2/5] do_div(): generic optimization for constant divisor on 32-bit machines |
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On Tue, 3 Nov 2015, Arnd Bergmann wrote:
> On Tuesday 03 November 2015 13:32:17 kbuild test robot wrote: > > > > net/can/bcm.c: In function 'bcm_proc_show': > > >> net/can/bcm.c:223:1: warning: the frame size of 1156 bytes is larger than 1024 bytes [-Wframe-larger-than=] > > } > > Interesting, that is a lot of stack for a function that only has a couple > of local variables: > > #define IFNAMSIZ 16 > char ifname[IFNAMSIZ]; > struct sock *sk = (struct sock *)m->private; > struct bcm_sock *bo = bcm_sk(sk); > struct bcm_op *op; > > > This is a parisc-allyesconfig kernel, so I assume that CONFIG_PROFILE_ALL_BRANCHES > is on, which instruments every 'if' in the kernel. If that causes problems, > we could decide to disable the do_div optimization whenever CONFIG_PROFILE_ALL_BRANCHES > is enabled.
I have an ARM allyesconfig build here where that function needs a frame of 88 bytes only. And that is with my do_div optimization applied.
With the do_div optimization turned off, the stack frame is still 88 bytes.
Turning on CONFIG_PROFILE_ALL_BRANCHES makes the frame size to grow to 96 bytes.
Keeping CONFIG_PROFILE_ALL_BRANCHES=y and activating the do_div optimization again, and the function frame size goes back to 88 bytes.
So I wonder what parisc gcc could be doing with this code.
Nicolas
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