Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Nov 24, 2009 at 03:32:20PM +0000, Andrew Haley wrote:
> Jakub Jelinek wrote:
> > On Tue, Nov 24, 2009 at 03:55:49PM +0100, Thomas Gleixner wrote:
> >>> you should compile your code with -maccumulate-outgoing-args, and there's
> >>> no need to use -mtune=generic.  Is that right?
> >> Seems to work. What other side effects has that ?
> > 
> > Faster code, significant increase in code size though.
> 
> Does it affect code size when we don't have to realign the stack pointer?

Yes, a lot.  The difference is that -maccumulate-outgoing-args allocates
space for arguments of the callee with most arguments in the prologue, using
subtraction from sp, then to pass arguments uses movl XXX, 4(%esp) etc.
and the stack pointer doesn't usually change within the function (except for
alloca/VLAs).
With -mno-accumulate-outgoing-args args are pushed using push instructions
and stack pointer is constantly changing.

	Jakub