Re: Breakpoint problem when running on gdb-4.18 arm/thumb simulator target

[Scott Bambrough <scottb at netwinder dot org>]

Kai Ruottu wrote:
> 
> "Lim, Sung-taek" wrote:
> >
>  Generally for the ARM-target it would be better to try the GDB snapshots. I don't
> remember this phenomen from my gdb-4.18.x's, but perhaps I had updated some ARM-stuff
> from the snapshots before building my first GDB for arm-elf...

This is true.  After the merge of the ARM Linux code, the number of testsuite
failures has fallen according to the last reports I got from Stan.

>  Some targets had their 'opcodes' changed for the simulated 'breakpoint' instruction,
> perhaps ARM was one of these. Anyway the synchronization between the binutils, GCC and
> GDB hasn't been the best, and one must try more than one release before getting the
> toolset to work. For arm-elf the '991130' and newer binutils seem to be broken. The
> linked executables will not load into older or current GDBs (like Insight).

ARM CPU's currently have no hardware support for breakpoints that I know of. 
GDB uses two approaches for breakpoints on ARM systems.  On systems such as ARM
Linux the OS has support for breakpoints in the kernel via a software
interrupt.  The instruction where the breakpoint occurs is replaced by a
software interrupt call into the kernel.  In embedded systems, with no such
kernel support, an undefined  instruction is used and GDB provides a handler for
the undefined instruction trap.  See the comments in tm-arm.h in the latest
snapshot for more detail.

> > the  patch can be found at:
> > http://poppy.snu.ac.kr/~totohero/arm-linux/gdb-4.18-dal-patch

The current snapshot should build and work fine for most things from what I
understand.

Scott

-- 
Scott Bambrough - Software Engineer
REBEL.COM    http://www.rebel.com
NetWinder    http://www.netwinder.org

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