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Some questions w.r.t remote watchpoint support in i386
- From: Wu Zhou <woodzltc at cn dot ibm dot com>
- To: gdb at sources dot redhat dot com
- Date: Tue, 25 Apr 2006 18:19:53 +0800 (CST)
- Subject: Some questions w.r.t remote watchpoint support in i386
I am playing with remote debugging on i386 platform. At the very first, I
start gdbserver and gdb on two different i386 machines. In this configuration,
local gdb client can connect to remote gdb server. But after I set a
breakpoint and issue "cont" command, remote debuggee get a SIGV error.
Then I start gdbserver and gdb on the same machine. There is no such
error any more. And it seems that most gdb commands work ok. But I
encounter some problems with h/w watchpoint operations. I did some
search, and don't find much information about my problems. So I choose to
1. The first error I encounter is: "Couldn't write debug register: No such
After some tracking, I found gdb client is calling target_insert_watchpoint
defined in config/i386/nm-i386.h, instead of the remote_insert_watchpoint
defined in remote.c
I guess this is a more general problem. Whenever you change target under
i386 platform, you will always get the i386_insert_watchpoint (and other
three target operations) executed.
Maybe we can put these target operation into the target_ops, instead of
defining them as macro in config/i386/nm-i386.h?
Any comments on this thought? Thanks.
2. Following the above thought, I comment out these four macros in
config/i386/nm-i386.h, and add them into i386-linux-nat.c
This time, local gdb will call remote_insert_watchpoint indeed, but I get
Can't clear hardware watchpoints without the 'Z2' (write-watchpoint) packet.
"set debug remote 1" tell me that Packet Z2 (write-watchpoint) is NOT
I tried to use "set remote write-watchpoint-packet 1", but it won't work
Enabled packet Z2 (write-watchpoint) not recognized by stub
my question here is:
What is the stub refered to here? Is it the gdbserver? And how can
gdbserver determine which packat he will support, which won't?
As far as I understand, now that the underlying target support hardware
watchpoint, there is not any practical obstacle for gdbserver on i386 to
support this kind of packets. If I am wrong, please forgive me and
correct me. (I am no expert in this field anyway. :-)
3. I also have a question about the overall status of gdb's support for
remote debugging on different platforms.
The available documents (gdb manual, gdb internal) don't mention much
information about this. I had thought that all commands avaialbe in local
gdb will also work in remote mode. But the practice prove that I am
wrong. Playing with remote debugging always make me feel a little
frustrated. (I am not very sure what other feels. I guess embedded
people will feel more comfortable. :-)
- Wu Zhou