On Wed, Jan 21, 2004 at 10:31:45PM +0530, Amit S. Kale wrote:

On Wednesday 21 Jan 2004 9:00 pm, Tom Rini wrote:

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On Wed, Jan 21, 2004 at 07:46:17PM +0530, Amit S. Kale wrote:

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Hi Tom,

Yes. Software breakpoints have been tested in the TimeSys ppc kernel
source. They work quite well!! I'll be releasing that code soon.

Any chance you can give me what they gave you?  I can try and merge
and test things.

Done.

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The breakpoint 0xc0000000 placed by gdb is _evil_ It may clobber data.
The gdb at kgdb.sourceforge.net places it correctly at module_event.

I'm not quite sure what you're getting at.   The gdb binary I'm using is
a good one (It's happy w/ the current kgdb stub, working in tandem w/ a
BDI2000, etc).  If the breakpoints being set aren't right, I suspect
that it's related to the other problems I'm seeing.

Stock gdb places a breakpoint to detect loading of shared libraries. Since
kernel doesn't have the symbols that ld-linux-* has, it places that at
begining of the kernel (or elsewhere I haven't been able to figure out
exactly where it places it). This breakpoint corrupts kernel data many a
times.

The gdb I maintain at kgdb.sourceforge.net places a breakpoint correctly at
module_event and detects loading of modules.

Ah, ok.

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Where is the other breakpoint placed? While you would have certainly done
that, please confirm that kgdb actually inserts a breakpoint where you
have asked it to: a simple printk at the address where the breakpoint is
placed should be sufficient. printing from gdb will not work as gdb
removes all breakpoints before giving control to a user.

The thing is the kernel gets into an infinite loop of stopping, as far
as gdb can tell, at the initial breakpoint

I thought you could place a breakpoint somewhere and the breakpoint was never
hit.

ok. Now I know where it went wrong: nip is instruction pointer, not
instruction contents. The change you had done compared nip to breakpoint
instruction contents.

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+       if (linux_regs->nip == 0x7d821008 )
+               /* Skip over breakpoint trap insn */
+               linux_regs->nip += 4;

Checking for kgdb_setting_breakpoint is better. Following code from my patch
is correct.

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+       extern atomic_t kgdb_setting_breakpoint;
+       if (atomic_read(&kgdb_setting_breakpoint))
+               regs->nip += 4;

I could have sworn I tried a number of combinations of things, including
that.  But I'm grabbing 2.1.0 now and will get back to you.

--
Tom Rini
http://gate.crashing.org/~trini/

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