[win32] Fix watchpoint support
Pedro Alves
pedro_alves@portugalmail.pt
Wed Nov 21 00:35:00 GMT 2007
Hi,
The current watchpoint support for native debugging on win32 systems
doesn't work reliably. Quite often, we'd miss that the inferior
stopped due to a watchpoint triggering, because Windows wouldn't
report in DR6 which watchpoint triggered. Take a look at this
"set debug infrun 1; maint show-debug-regs 1" snippet [1]:
infrun: TARGET_WAITKIND_STOPPED
infrun: stop_pc = 0x40108e
stopped_data_addr:
CONTROL (DR7): 000d0101 STATUS (DR6): 00000000
^^^^^^^^
DR0: addr=0x00403010, ref.count=1 DR1: addr=0x00000000, ref.count=0
DR2: addr=0x00000000, ref.count=0 DR3: addr=0x00000000, ref.count=0
infrun: random signal 5
^^^^^^^^^^^^^^^^^^^^^^^
Program received signal SIGTRAP, Trace/breakpoint trap.
infrun: stop_stepping
remove_watchpoint (addr=403010, len=4, type=data-write):
CONTROL (DR7): 000d0100 STATUS (DR6): 00000000
DR0: addr=0x00000000, ref.count=0 DR1: addr=0x00000000, ref.count=0
DR2: addr=0x00000000, ref.count=0 DR3: addr=0x00000000, ref.count=0
main () at watch.c:11
11 printf ("count %d\n", count);
0x00403010 in that example is the address of a variable that
was just written to.
[1] Full example here:
http://cygwin.com/ml/cygwin/2007-10/msg00057.html
I ended up tracing the problem to win32_continue (gdb/win32-nat.c).
Currently, it looks somewhat like this:
1 win32_continue(TID)
2 ContinueDebugEvent(current_TID)
3 foreach thread in threads do
4 if thread == TID
5 ResumeThread(TID)
6 SetThreadContext(TID, DEBUG_REGS)
7 fi
8 hcaerof
The first problem is that we shoudn't be calling
SetThreadContext after ResumeThread (5,6) -- it should
be the other way around.
Second, when TID represents the thread of the
current debug event, TID will already be resumed
after the ContinueDebugEvent call, because we don't
call SuspendThread on the current debug event thread.
This is what caused the weird watchpoint behaviour.
I can see more than one way to fix this :
1 - Only call ContinueDebugEvent after resuming and setting
the context on every other thread:
1 win32_continue(TID)
2 foreach thread in threads do
3 if thread == TID
4 ResumeThread(TID)
5 SetThreadContext(TID, DEBUG_REGS)
6 fi
7 hcaerof
8 ContinueDebugEvent(current_TID)
2 - Don't ResumeThread/SetThreadContext on the thread of
the current debug event, since it is already set in
win32_resume:
1 win32_continue(TID)
2 foreach thread in threads do
3 if thread == TID && thread != current_TID
4 ResumeThread(TID)
5 SetThreadContext(TID, DEBUG_REGS)
6 fi
7 hcaerof
8 ContinueDebugEvent(current_TID)
I tend to prefer the first, because win32_continue isn't
always called from win32_resume, and because until
ContinueDebugEvent is called, all threads are stopped. The
second choice isn't as atomic.
The attached patch implements option 1. It fixes a
bunch of watchpoint related failures on Cygwin, and has
no regressions:
PASS: gdb.base/commands.exp: add print command to watch
PASS: gdb.base/commands.exp: add continue command to watch
PASS: gdb.base/commands.exp: end commands on watch
-FAIL: gdb.base/commands.exp: continue with watch
+PASS: gdb.base/commands.exp: continue with watch
PASS: gdb.base/commands.exp: break factorial #3
PASS: gdb.base/commands.exp: set value to 5 in test_command_prompt_position
PASS: gdb.base/commands.exp: if test in test_command_prompt_position
PASS: gdb.base/display.exp: display &k
PASS: gdb.base/display.exp: display/f f
PASS: gdb.base/display.exp: display/s &sum
-FAIL: gdb.base/display.exp: first disp
-FAIL: gdb.base/display.exp: second disp
+PASS: gdb.base/display.exp: first disp
+PASS: gdb.base/display.exp: second disp
PASS: gdb.base/display.exp: catch err
PASS: gdb.base/display.exp: disab disp 1
PASS: gdb.base/display.exp: disab disp 2
PASS: gdb.base/display.exp: re-enab of enab
PASS: gdb.base/display.exp: undisp
PASS: gdb.base/display.exp: info disp
-FAIL: gdb.base/display.exp: next hit
+PASS: gdb.base/display.exp: next hit
PASS: gdb.base/display.exp: undisp all
PASS: gdb.base/display.exp: disab 3
PASS: gdb.base/display.exp: watch off
Running ../../../gdb-server_submit/src/gdb/testsuite/gdb.base/recurse.exp ...
PASS: gdb.base/recurse.exp: next over b = 0 in first instance
PASS: gdb.base/recurse.exp: set first instance watchpoint
-FAIL: gdb.base/recurse.exp: continue to first instance watchpoint, first time
+PASS: gdb.base/recurse.exp: continue to first instance watchpoint, first time
PASS: gdb.base/recurse.exp: continue to recurse (a = 9)
PASS: gdb.base/recurse.exp: continue to recurse (a = 8)
PASS: gdb.base/recurse.exp: continue to recurse (a = 7)
PASS: gdb.base/recurse.exp: continue to recurse (a = 5)
PASS: gdb.base/recurse.exp: next over b = 0 in second instance
PASS: gdb.base/recurse.exp: set second instance watchpoint
-FAIL: gdb.base/recurse.exp: continue to second instance watchpoint, first time
+PASS: gdb.base/recurse.exp: continue to second instance watchpoint, first time
PASS: gdb.base/recurse.exp: continue to recurse (a = 4)
PASS: gdb.base/recurse.exp: continue to recurse (a = 3)
PASS: gdb.base/recurse.exp: continue to recurse (a = 2)
PASS: gdb.base/recurse.exp: continue to recurse (a = 1)
-FAIL: gdb.base/recurse.exp: continue to second instance watchpoint, second time
+PASS: gdb.base/recurse.exp: continue to second instance watchpoint, second time
PASS: gdb.base/recurse.exp: second instance watchpoint deleted when leaving
scope
-FAIL: gdb.base/recurse.exp: continue to first instance watchpoint, second time
+PASS: gdb.base/recurse.exp: continue to first instance watchpoint, second time
PASS: gdb.base/recurse.exp: first instance watchpoint deleted when leaving
scope
PASS: gdb.base/watchpoint.exp: break func1
PASS: gdb.base/watchpoint.exp: set $func1_breakpoint_number = $bpnum
PASS: gdb.base/watchpoint.exp: continue to breakpoint at func1
-FAIL: gdb.base/watchpoint.exp: watchpoint hit, first time
-FAIL: gdb.base/watchpoint.exp: watchpoints found in watchpoint/breakpoint table
+PASS: gdb.base/watchpoint.exp: watchpoint hit, first time
+PASS: gdb.base/watchpoint.exp: Watchpoint hit count is 1
+PASS: gdb.base/watchpoint.exp: delete $func1_breakpoint_number
+PASS: gdb.base/watchpoint.exp: watchpoint hit, second time
+PASS: gdb.base/watchpoint.exp: Watchpoint hit count is 2
+PASS: gdb.base/watchpoint.exp: watchpoint hit, third time
+PASS: gdb.base/watchpoint.exp: Watchpoint hit count is 3
+PASS: gdb.base/watchpoint.exp: watchpoint hit, fourth time
+PASS: gdb.base/watchpoint.exp: Watchpoint hit count is 4
+PASS: gdb.base/watchpoint.exp: watchpoint hit, fifth time
+PASS: gdb.base/watchpoint.exp: Watchpoint hit count is 5
+PASS: gdb.base/watchpoint.exp: continue to marker2
+PASS: gdb.base/watchpoint.exp: watchpoint disabled
+PASS: gdb.base/watchpoint.exp: continue until exit at continue to exit in
test_simple_watchpoint
+PASS: gdb.base/watchpoint.exp: watchpoints found in watchpoint/breakpoint table
PASS: gdb.base/watchpoint.exp: disable watchpoint in test_disabling_watchpoints
PASS: gdb.base/watchpoint.exp: run to marker1 in test_disabling_watchpoints
PASS: gdb.base/watchpoint.exp: watchpoint enabled
-FAIL: gdb.base/watchpoint.exp: watchpoint hit in test_disabling_watchpoints,
first time
-FAIL: gdb.base/watchpoint.exp: watchpoint hit in test_disabling_watchpoints,
second time
+PASS: gdb.base/watchpoint.exp: watchpoint hit in test_disabling_watchpoints,
first time
+PASS: gdb.base/watchpoint.exp: watchpoint hit in test_disabling_watchpoints,
second time
PASS: gdb.base/watchpoint.exp: disable watchpoint #2 in
test_disabling_watchpoints
PASS: gdb.base/watchpoint.exp: watchpoint disabled in table
PASS: gdb.base/watchpoint.exp: disabled watchpoint skipped
PASS: gdb.mi/mi-watch.exp: hw: mi runto callee4
PASS: gdb.mi/mi-watch.exp: hw: break-watch operation
PASS: gdb.mi/mi-watch.exp: hw: list of watchpoints
-FAIL: gdb.mi/mi-watch.exp: hw: watchpoint trigger (2)
+PASS: gdb.mi/mi-watch.exp: hw: watchpoint trigger
PASS: gdb.mi/mi-watch.exp: hw: wp out of scope
PASS: gdb.mi/mi2-watch.exp: hw: break-watch operation
PASS: gdb.mi/mi2-watch.exp: hw: list of watchpoints
-FAIL: gdb.mi/mi2-watch.exp: hw: watchpoint trigger (2)
+PASS: gdb.mi/mi2-watch.exp: hw: watchpoint trigger
PASS: gdb.mi/mi2-watch.exp: hw: wp out of scope
PASS: gdb.threads/watchthreads.exp: successfully compiled posix threads test
case
PASS: gdb.threads/watchthreads.exp: watch args[0]
PASS: gdb.threads/watchthreads.exp: watch args[1]
-FAIL: gdb.threads/watchthreads.exp: threaded watch loop
-FAIL: gdb.threads/watchthreads.exp: first watchpoint on args[0] hit
-FAIL: gdb.threads/watchthreads.exp: first watchpoint on args[1] hit
-FAIL: gdb.threads/watchthreads.exp: watchpoint on args[0] hit in thread
-FAIL: gdb.threads/watchthreads.exp: watchpoint on args[1] hit in thread
-FAIL: gdb.threads/watchthreads.exp: combination of threaded watchpoints = 30
+PASS: gdb.threads/watchthreads.exp: threaded watch loop
+PASS: gdb.threads/watchthreads.exp: first watchpoint on args[0] hit
+PASS: gdb.threads/watchthreads.exp: first watchpoint on args[1] hit
+PASS: gdb.threads/watchthreads.exp: watchpoint on args[0] hit in thread
+PASS: gdb.threads/watchthreads.exp: watchpoint on args[1] hit in thread
+PASS: gdb.threads/watchthreads.exp: combination of threaded watchpoints = 30
OK ?
--
Pedro Alves
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