Re: [RFC PATCH 01/11] Add basic support for gcc profiler instrumentation

[Jeremy Fitzhardinge <jeremy@goop.org>]

Chris Wright wrote:
> * Steven Rostedt (rostedt@goodmis.org) wrote:
>   
>> Hmm, I know paravirt-ops had an issue with mcount in the RT tree. I can't
>> remember the exact issues, but it did have something to do with the way
>> parameters were passed in.
>>
>> Chris, do you remember what the issues were?
>>     
>
> Yes, paravirt ops have a well-specified calling convention (register
> based).  There was a cleanup that Andi did that caused the problem
> because it removed all the "fastcall" annotations since -mregparm=3
> is now always on for i386.  Since MCOUNT disables REGPARM the calling
> convention changes (caller pushes to stack, callee expects register)
> chaos ensues.  I sent a patch to fix that quite some months back, but
> it went stale and I neglected to update it.  Would you like me to dig
> it up refresh and resend?

Ingo/Andrew have been accepting patches to systematically remove all the
fastcall annotations from the kernel, so adding them back isn't going to
help.

Ingo and I discussed whether we need to reannotate paravirt.h (either
with fastcall or something else indicating a register-only calling
convention), specifically because of the -pg issue, but I think the
conclusion was that whatever problem existed no longer does, and there's
no incompatibility between -pg and regparm.

    J