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Re: [RFC] Unified watchpoints for x86 platforms
Eli Zaretskii <firstname.lastname@example.org> writes:
> While writing the code for the x86 watchpoint support, a question
> popped up regarding the Global Enable and Local Enable flags in the
> DR7 (Debug Control) register.
> For those who might not remember what those flags are: Each
> hardware-assisted breakpoint or watchpoint should be enabled by
> setting bits in the DR7 register. A watchpoint can be enabled locally
> or globally, depending on which bit in DR7 is set for that watchpoint.
> A watchpoint that is enabled locally will only break if it is hit in
> the current task. A watchpoint that is enabled globally will break in
> any task.
Makes me wonder if global watchpoints would really work if hardware
task switching isn't used.
Anyway, I guess most x86 OS'es wouldn't allow any real global
watchpoints. For Linux it doesn't matter whether you set the local or
the global bit.
> Now, I understand that, by and large, x86 platforms enable watchpoints
> locally, to avoid spurious traps triggered by other processes. If
> that is true, should the code I write use the Local Enable flag
> unconditionally? Or perhaps it would be useful to define an API that
> enables a target to control whether the global or local enable flag is
In principle a GDB command to control whether to enable watchpoints
locally or globally wouldn't be a bad idea. But I don't know any
targets where this would be useful. So if it isn't useful for DJGPP
either, I wouldn't bother. A comment about the issue at the right
spot would be nice though.