Re: Debug ARM semihosting Thumb-2 binary

[Matthew Gretton-Dann <matthew dot gretton-dann at arm dot com>]

On Wed, Feb 08, 2012 at 10:34:18AM +0000, Jonas Maebe wrote:
> Hi,
> 
> I'm debugging ARM binaries compiled for the semihosting interface (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/CHDJHHDI.html 
>   ). The binaries run under qemu-system-arm and I'm using QEMU's gdb  
> remote target interface.
> 
> In general, this works fine, except when such binaries are Thumb-2 and  
> perform system calls. The reason is that for Thumb-2, the system call  
> interface of the semihosting platform uses "bkpt 0xab" (http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491c/CJAFABBB.html 
>   ). GDB intercepts this bkpt, halts the execution with a SIGINT  
> message and does not pass it on to the debugged process. If the  
> process is then continued, it behaves as if the system call/bkpt in  
> question never was executed
> 
> Using "handle SIGINT pass" does not change this.
> 
> Is there another way to tell gdb to ignore those particular bkpt  
> instructions and execute them normally? I'm using gdb 7.4 (7.2 behaves  
> the same).

What CPU are you compiling for?  The docs aren't clear but BKPT should only be used
for Cortex-M CPUs - otherwise 'svc 0xab' is appropriate in ARM state.

However, I know there have been issues with libgloss/newlib using the wrong
semi-hosting call sequence in some cases.

Try updating newlib (if that is what you are using) if you are compiling for
non-Cortex-M systems.  If you are compiling for a Cortex-M CPU then I
believe things should work.

Thanks,

Matt

-- 
Matthew Gretton-Dann
Principal Engineer, PD Software, ARM Ltd.