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Re: i386 debugging registers
- To: Mark Kettenis <kettenis at wins dot uva dot nl>
- Subject: Re: i386 debugging registers
- From: Fernando Nasser <fnasser at cygnus dot com>
- Date: Sun, 11 Jun 2000 23:32:28 +0000
- CC: gdb at sourceware dot cygnus dot com, nsd at cygnus dot com, Peter dot Schauer at regent dot e-technik dot tu-muenchen dot de, rjl at sco dot com, eliz at gnu dot org, cgf at cygnus dot com, jtc at redback dot com, jimb at cygnus dot com
- Organization: Red Hat Canada Ltd. - Toronto
- References: <200006112322.e5BNM6513971@delius.kettenis.local>
I can see one situation where one may want to look at or set debugger registers:
when debugging a debugger's hardware breakpoint support. So, I believe we should
leave these registers out of the users sight.
As a compromise, I suggest that we add (I will do the same on my targets around
here) a pair of "qQ" packets to read/write those registers.
What I mean is:
We can add a maintenance command to access that. That is what maintenance
commands are for.
What do you think? Would that solve your problem?
Mark Kettenis wrote:
> While trying to build a generic layer for implementing hardware
> watchpoint for the various i386 native ports, I found myself starting
> to implement some sort of register cache for the debugging registers.
> Instead actually doing so, I wondered whether it would be a good idea
> to add the debug registers to the standard register cache.
> * It makes my life easier :-)
> * They are, you know, erh... registers.
> * Some people might actually want to fiddle with them, especially
> with the control register which has some bits that control the
> instruction pipeline.
> * It might confuse our users. Fiddling with the debug registers
> might interfere with the hardware watchpoint support. For example,
> Assigning to one of the address registers will probably make GDB
> forget about some hardware watchpoints and produce some weird
> warnings. It will also likely cause some spurious SIGTRAPS.
> * The exact effect of modifying the debugging registers is somewhat
> dependent on the underlying OS. To make sure GDB's hardware
> watchpoints work as expected, some additional frobbing of the
> debugging might be necessary in the code that actually fetches
> and/or stores the registers. The user will see those frobbed
> registers instead of the real ones.
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