Re: [PATCH -v4 9/9] tracing: add function graph tracer support forMIPS

[David Daney]

Steven Rostedt wrote:
> On Thu, 2009-10-22 at 08:59 -0700, David Daney wrote:
>
> > This is what I was talking about up-thread.  Leaf functions may have no 
> > function prolog.  If you do code scanning you will fail.  While scanning 
> > backwards, there is no way to know when you have entered a new function. 
> >   Looking for function return sequences 'jr ra' doesn't work as there 
> > may be functions with multiple return sites, functions that never 
> > return, or arbitrary data before the function.  I think you have to 
> > force a frame pointer to be established if you want this to work.
>
> Functions that run off into another function?? I guess the compiler
> could do that, but with -pg enable, I would think is broken.

Use of GCC-4.5's __builtin_unreachable() can lead to this, as well as 
functions that call noreturn functions.


Note to self: Time to resend the __builtin_unreachable() patch set again...

David Daney
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