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

[Richard Earnshaw <rearnsha@gcc.gnu.org>]

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.