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gdbstub: add reverse step support in replay mode

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GDB remote protocol supports two reverse debugging commands:
reverse step and reverse continue.
This patch adds support of the first one to the gdbstub.
Reverse step is intended to step one instruction in the backwards
direction. This is not possible in regular execution.
But replayed execution is deterministic, therefore we can load one of
the prior snapshots and proceed to the desired step. It is equivalent
to stepping one instruction back.
There should be at least one snapshot preceding the debugged part of
the replay log.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

--

v4 changes:
 - inverted condition in cpu_handle_guest_debug (suggested by Alex Bennée)
Message-Id: <160174522341.12451.1498758422543765253.stgit@pasha-ThinkPad-X280>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Pavel Dovgalyuk 2020-10-03 20:13:43 +03:00 • committed by Paolo Bonzini
parent f9a9fb6516
commit fda8458bd3
7 changed files with 122 additions and 5 deletions
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7
exec.c
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@ -2748,6 +2748,13 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
QTAILQ_FOREACH(wp, &cpu->watchpoints, entry) {
if (watchpoint_address_matches(wp, addr, len)
&& (wp->flags & flags)) {
if (replay_running_debug()) {
/*
* Don't process the watchpoints when we are
* in a reverse debugging operation.
*/
return;
}
if (flags == BP_MEM_READ) {
wp->flags |= BP_WATCHPOINT_HIT_READ;
} else {