lkml.org 
[lkml]   [2009]   [Nov]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: BUG: GCC-4.4.x changes the function frame on some functions
Linus Torvalds wrote:
>
> On Thu, 19 Nov 2009, Linus Torvalds wrote:
>> I bet other people than just the kernel use the mcount hook for subtler
>> things than just doing profiles. And even if they don't, the quoted code
>> generation is just crazy _crap_.
>
> For the kernel, if the only case is that timer_stat.c thing that Thomas
> pointed at, I guess we can at least work around it with something like the
> appended. The kernel code is certainly ugly too, no question about that.
>
> It's just that we'd like to be able to depend on mcount code generation
> not being insane even in the presense of ugly code..
>
> The alternative would be to have some warning when this happens, so that
> we can at least see it. "mcount won't work reliably"
>

For the MIPS port of GCC and Linux I recently added the
-mmcount-ra-address switch. It causes the location of the return
address (on the stack) to be passed to mcount in a scratch register.

Perhaps something similar could be done for x86. It would make this
patching of the return location more reliable at the expense of more
code at the mcount invocation site.

For the MIPS case the code size doesn't increase, as it is done in the
delay slot of the call instruction, which would otherwise be a nop.

David Daney


\
 
 \ /
  Last update: 2009-11-19 20:13    [W:0.141 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site