32-bit Thumb-2 breakpoints

Daniel Jacobowitz dan at debian.org
Wed Feb 3 12:44:26 EST 2010

On Wed, Feb 03, 2010 at 05:23:01PM +0000, Jamie Lokier wrote:
> Daniel Jacobowitz wrote:
> > Thankfully, both branches into IT blocks and branches
> > leaving IT blocks not at the last instruction are forbidden.
> Forbidden as in throws a fault, or forbidden as in "can we use this to
> break out of GDB single-stepping to give third-parties a hard time
> tracing my secret code"?

Forbidden as in "the architecture documentation says it has
unpredictable behavior".

That's generally where I draw the line at trying to handle bad code.
In practice, I will make a wild guess that current processors fault
branches during an IT block and don't do anything fancy for branches
into an IT block, or else it messes up in some hard-to-reproduce way.

Daniel Jacobowitz

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