[Qemu-devel] Help with gdb on Mac OS

[Qemu-devel] Help with gdb on Mac OS

[Ilya Shar]

I am trying to step through i386-darwin-user/qemu-i386
in gdb but I am getting a KERN_PROTECTION_FAILURE
fairly early in the run: 

(gdb) run /bin/ls
Starting program:
/Users/ilya/tmp/feb11/qemu-0.9.0/i386-darwin-user/qemu-i386
/bin/ls
Reading symbols for shared libraries . done
Starting /bin/ls with qemu
----------------

Program received signal EXC_BAD_ACCESS, Could not
access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x2115eaf5
helper_cmpxchg8b () at ../cpu-all.h:344
344         ((uint32_t *)ptr)[0] = x.p[0];
(gdb) 

The offending value of ptr is misalligned, can this
indicate a problem?  Reducing optimization or setting
-g3 doesn't change this behavior.  Strangely, the same
example runs fine without gdb. 

Is there any way to correct the gdb problem?  I am
using gdb 6.3 on Mac OS Intel with QEMU 0.9.0 and
patches for gcc4/Mac posted by Mike Kronenberg.  

Thanks for your help, 
Ilya 



 
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Re: [Qemu-devel] Help with gdb on Mac OS

[Pierre d'Herbemont]

On 12 févr. 07, at 07:54, Ilya Shar wrote:

> I am trying to step through i386-darwin-user/qemu-i386
>
> Program received signal EXC_BAD_ACCESS, Could not
> access memory.
> Reason: KERN_PROTECTION_FAILURE at address: 0x2115eaf5
> helper_cmpxchg8b () at ../cpu-all.h:344
> 344         ((uint32_t *)ptr)[0] = x.p[0];
> (gdb)
>
> The offending value of ptr is misalligned, can this
> indicate a problem?  Reducing optimization or setting
> -g3 doesn't change this behavior.  Strangely, the same
> example runs fine without gdb.

qemu will handle the signal fine. Actually it is more a feature than  
a bug ;-)

Unfortunately
"(gdb) handle EXC_BAD_ACCESS pass"
is kind of broken as EXC_BAD_ACCESS is not translated to the  
corresponding bsd signal, so qemu won't handle it.

You should probably try to use the gdb interface provided by qemu if  
you wan't to debug the target program instead of qemu:
# i386-darwin-user/qemu-i386 -g /bin/ls

You can now connect to the gdb interface using:
#gdb -arch i386
(gdb) target remote localhost:1234
(gdb) c

Pierre.