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SubjectRe: [PATCH -v4 9/9] tracing: add function graph tracer support for MIPS
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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