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Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- From: Andrew Haley <aph at redhat dot com>
- To: Ross Ridge <rridge at csclub dot uwaterloo dot ca>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 24 Nov 2009 17:11:43 +0000
- Subject: Re: [PATCH][GIT PULL][v2.6.32] tracing/x86: Add check to detect GCC messing with mcount prologue
- References: <20091124170457.2E96F1D8D1@caffeine.csclub.uwaterloo.ca>
Ross Ridge wrote:
> Andrew Haley writes:
>> Alright. So, it is possible in theory for gcc to generate code that
>> only uses -maccumulate-outgoing-args when it needs to realign SP.
>> And, therefore, we could have a nice option for the kernel: one with
>> (mostly) good code density and never generates the bizarre code
>> sequence in the prologue.
>
> The best option would be for the Linux people to fix the underlying
> problem in their kernel sources. If the code no longer requested
> that certain automatic variables be aligned, then not only would this
> bizarre code sequence not be emitted, the unnecessary stack alignment
> would disapear as well. The kernel would then be free to choose to use
> whatever code generation options it felt was appropriate.
Well, yeah. But, for my sins, I tend to assume that the Linux kernel
people have some kind of reason for the things they do. Working with
them over the years has helped us improve gcc, even though at times
things get to be a little ill-tempered.
Andrew.