Re: [Qemu-devel] Re: [PATCH] i386 debugging stubs: Consider segment bases

[Eddie Kohler <kohler@cs.ucla.edu>]

Thanks for the response.  I agree the patch is a workaround, but it is a 
useful workaround, and I'd still argue for including it.

The patch doesn't *require* that CS.base == DS.base.  Breakpoints 
correctly and exclusively use CS.base.  However, any memory examination 
uses DS.base, and you're right that the user might "want" to examine 
some other segment.  A GDB fix would involve changing the gdb remote 
protocol as well as GDB itself and the GDB user interface.  Google says 
you've been thinking about that for a while now -- is it going well?

> For the time being, you should be able to workaround the gdb limitation
> by setting two breakpoints: one on the linear address and another one on
> the CS offset. Not nice, but used to work for us.

I don't mind the double-breakpoint as much, but memory examination would 
still be broken, yes?

I don't understand the comment about "prevents setting breakpoints on 
inactive segments."  The code for setting breakpoints has not changed.

Do you think the patch would actually make debugging WORSE on any OS? 
Or have any other undesirable effects, or make it harder to DTRT when 
GDB is ready?  It seems safe & useful to me; & it's 2 LOC!

Eddie