Re: [PATCH] gdb/x86: Fix write out of mxcsr register for xsave targets

[Pedro Alves <palves@redhat.com>]

On 05/11/2018 12:52 PM, Andrew Burgess wrote:
> In commit:
> 
>   commit 8ee22052f690c007556b97eed59f49350ece5ca9
>   Author: Andrew Burgess <andrew.burgess@embecosm.com>
>   Date:   Thu May 3 17:46:14 2018 +0100
> 
>       gdb/x86: Handle kernels using compact xsave format
> 
> in two places FXSAVE_ADDR was used instead of FXSAVE_MXCSR_ADDR to get
> the address of the mxcsr register within the xsave buffer.  This will
> mean we are potentially accessing the wrong location within the xsave
> buffer.
> 
> There are no tests included with this patch.  The first mistake would
> only trigger an issue if/when the user tries to manually set the mxcsr
> register to a value that matches the random (value off stack) value
> that is in the xsave buffer, in this case the change by the user will
> go unnoticed by GDB, and the default value of mxcsr will be preserved.
> 
> The second mistake only happens on the code path where all x87
> registers are being written out of the register cache.  I'm not sure
> how to trigger that code path.
> 

OK as is.

How did you notice this?  Valgrind?

Thanks,
Pedro Alves