MicroBlaze QEMU skips jumps when using single steps in GDB

[Stephan Vogt]

I'm trying to debug a MicroBlaze application (with the MicroBlaze system qemu, not the user mode qemu) using GDB. When I'm trying to single step through instructions all the branches are ignored: the program counter is just incremented by 4 (default), even for unconditional branches. This only occurs when using single step mode, everything runs as expected when using breakpoints only.

Qemu Versions tested: 0.11.0, 0.12.3, GIT version (March 29, 2010)
Qemu command used: qemu-system-microblaze -kernel test.elf -S -s

GDB Versions used: 7.1 (official MicroBlaze support), 6.5 (from Xilinx EDK 10.1), 5.3 (from Xilinx EDK 9.1)
GCC Versions used: 4.1.1 (from Xilinx EDK 11.1)

I've attached my program, it uses a custom linker script and startup code. It runs fine without using singlestep mode.

The bug looks similar to one submitted for PPC a while ago (181951).

[Christophe (ccoutand)]

I'm having a similar issue with Qemu 0.13.0, program counter is just incremented by 4 when single stepping. I am using GDB 7.2. Stephan, did you get it to work in single step mode?

[Edgar E. Iglesias (edgar-iglesias)]

Hi,

I've committed a patch (that I hope fixes this problem) into the qemu git repo.

Cheers

Look for the following commit:
commit 6c5f738daec123020d32543fe90a6633a4f6643e
Author: Edgar E. Iglesias <email address hidden>
Date: Thu Feb 10 00:46:09 2011 +0100

    microblaze: Handle singlestepping over direct jmps

    Signed-off-by: Edgar E. Iglesias <email address hidden>

[Christophe (ccoutand)]

Thanks for the patch, so far so good...

Christophe