[Bug target/18929] Profiling optimized code causes segfaults on ARM due to missing frames

["opensource at artnaseef dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From opensource at artnaseef dot com  2004-12-13 15:55 -------
Subject: Re:  Profiling optimized code causes segfaults on
 ARM due to missing frames

Alright, since my instructions are not good enough for you, I will
put together an example.


rearnsha at gcc dot gnu dot org wrote:

>------- Additional Comments From rearnsha at gcc dot gnu dot org  2004-12-13 15:43 -------
>Subject: Re:  Profiling optimized code causes segfaults
>	on ARM due to missing frames
>
>On Mon, 2004-12-13 at 15:28, opensource at artnaseef dot com wrote:
>
>>------- Additional Comments From opensource at artnaseef dot com  2004-12-13 15:28 -------
>>Subject: Re:  Profiling optimized code causes segfaults on
>> ARM due to missing frames
>>
>>Two things
>>
>>  1. Why do you not think the  patch is correct?  It works great for 
>>me.  Without
>>     that information, I can only respond with "I think you are wrong," 
>>and that
>>     is not productive.
>>
>>
>Because I don't think profiling should need the a frame pointer to
>work.  If it does, then my feeling is that it's the profiling code
>that's broken, not the compiler.  The layout of a stack frame is private
>to the function that built it, and any code outside of that function
>that tries to probe it is simply broken.
>
>
>>  2. The comment in the patch you show is that the Profiler clobbers the 
>>Link
>>     Register.  That is NOT this problem.
>>
>>
>
>Well, that patch was never applied to the 3.3 branch.  The bug it refers
>to was reported against 3.0, so there's a strong likelihood that it will
>be needed in 3.3 as well.
>
>
>>In this problem, the profiler causes a segmentation fault when it reads 
>>the wrong
>>return address off the stack and uses it as an invalid function 
>>address.  It does
>>not use the link register value.
>>
>>To reproduce the problem:
>>
>>  - Build an arm-linux toolchain
>>
>>  - Compile a program with optimization and profiling (try -O2 and -pg).
>>
>>     - Make sure the program includes a function for which the optimizer
>>       drops its frame pointer (this can easily be verified by looking at
>>       the assembly output of the compiler).
>>
>>  - Run the program.
>>
>>If a trace is needed, I will be able to produce one within a few days
>>and provide an example.  Note that this problem was quite easy for me
>>to reproduce, so I would expect reproducing it to be simple enough for
>>others.
>>
>
>I'm not in the business of trying to second guess how you encountered a
>problem.  If you want us to investigate a bug then you need to send us
>precise instructions (including source code) so that we can reproduce
>it.
>
>
>



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18929