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authorPedro Alves <pedro@palves.net>2024-05-07 13:57:47 +0100
committerPedro Alves <pedro@palves.net>2024-05-17 20:14:26 +0100
commit7d6c04c5807753e5ad485eea6f4ce0946d4f1443 (patch)
tree631bdc886e4a9ecc2ad0c4183645377b671a0f3e
parent650daf18185de6d2e51da2fe5cd0b94cc7fb9174 (diff)
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Windows gdb: Watchpoints while running (internal vs external stops)
Teach the Windows target to temporarily pause all threads when we change the debug registers for a watchpoint. Implements the same logic as Linux uses: ~~~ /* (...) if threads are running when the mirror changes, a temporary and transparent stop on all threads is forced so they can get their copy of the debug registers updated on re-resume. (...) */ ~~~ On Linux, we send each thread a SIGSTOP to step them. On Windows, SuspendThread itself doesn't cause any asynchronous debug event to be reported. However, we've implemented windows_nat_target::stop such that it uses SuspendThread, and then queues a pending GDB_SIGNAL_0 stop on the thread. That results in a user-visible stop, while here we want a non-user-visible stop. So what we do is re-use that windows_nat_target::stop stopping mechanism, but add an external vs internal stopping kind distinction. An internal stop results in windows_nat_target::wait immediately re-resuming the thread. Note we don't make the debug registers poking code SuspendThread -> write debug registers -> ContinueThread itself, because SuspendThread is actually asynchronous and may take a bit to stop the thread (a following GetThreadContext blocks until the thread is actually suspended), and, there will be several debug register writes when a watchpoint is set, because we have to set all of DR0, DR1, DR2, DR3, and DR7. Defering the actualy writes to ::wait avoids a bunch of SuspendThread/ResumeThread sequences, so in principle should be faster. Change-Id: I39c2492c7aac06d23ef8f287f4afe3747b7bc53f
-rw-r--r--gdb/nat/windows-nat.h27
-rw-r--r--gdb/windows-nat.c116
2 files changed, 119 insertions, 24 deletions
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index cf6889b..98ea4ba 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -34,6 +34,24 @@ namespace windows_nat
struct windows_process_info;
+/* The reason for explicitly stopping a thread. Note the enumerators
+ are ordered such that when comparing two stopping_kind's numerical
+ value, the highest should prevail. */
+enum stopping_kind
+ {
+ /* Not really stopping the thread. */
+ SK_NOT_STOPPING = 0,
+
+ /* We're stopping the thread for internal reasons, the stop should
+ not be reported as an event to the core. */
+ SK_INTERNAL = 1,
+
+ /* We're stopping the thread for external reasons, meaning, the
+ core/user asked us to stop the thread, so we must report a stop
+ event to the core. */
+ SK_EXTERNAL = 2,
+ };
+
/* Thread information structure used to track extra information about
each thread. */
struct windows_thread_info
@@ -117,9 +135,10 @@ struct windows_thread_info
int suspended = 0;
/* This flag indicates whether we are explicitly stopping this
- thread in response to a target_stop request. This allows
- distinguishing between threads that are explicitly stopped by the
- debugger and threads that are stopped due to other reasons.
+ thread in response to a target_stop request or for
+ backend-internal reasons. This allows distinguishing between
+ threads that are explicitly stopped by the debugger and threads
+ that are stopped due to other reasons.
Typically, when we want to stop a thread, we suspend it, enqueue
a pending GDB_SIGNAL_0 stop status on the thread, and then set
@@ -128,7 +147,7 @@ struct windows_thread_info
already has an event to report. In such case, we simply set the
'stopping' flag without suspending the thread or enqueueing a
pending stop. See stop_one_thread. */
- bool stopping = false;
+ stopping_kind stopping = SK_NOT_STOPPING;
/* Info about a potential pending stop.
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index dfb5601..494fc1e 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -261,6 +261,10 @@ enum windows_continue_flag
all-stop mode. This flag indicates that windows_continue
should call ContinueDebugEvent even in non-stop mode. */
WCONT_CONTINUE_DEBUG_EVENT = 4,
+
+ /* Skip calling ContinueDebugEvent even in all-stop mode. This is
+ the default in non-stop mode. */
+ WCONT_DONT_CONTINUE_DEBUG_EVENT = 8,
};
DEF_ENUM_FLAGS_TYPE (windows_continue_flag, windows_continue_flags);
@@ -521,6 +525,8 @@ struct windows_nat_target final : public x86_nat_target<inf_child_target>
return serial_event_fd (m_wait_event);
}
+ void debug_registers_changed_all_threads ();
+
private:
windows_thread_info *add_thread (ptid_t ptid, HANDLE h, void *tlb,
@@ -528,7 +534,8 @@ private:
void delete_thread (ptid_t ptid, DWORD exit_code, bool main_thread_p);
DWORD fake_create_process (const DEBUG_EVENT &current_event);
- void stop_one_thread (windows_thread_info *th);
+ void stop_one_thread (windows_thread_info *th,
+ enum stopping_kind stopping_kind);
BOOL windows_continue (DWORD continue_status, int id,
windows_continue_flags cont_flags = 0);
@@ -1295,7 +1302,7 @@ windows_per_inferior::handle_output_debug_string
a pending event. It will be picked up by
windows_nat_target::wait. */
th->suspend ();
- th->stopping = true;
+ th->stopping = SK_EXTERNAL;
th->last_event = {};
th->pending_status.set_stopped (gotasig);
@@ -1608,7 +1615,7 @@ windows_per_inferior::continue_one_thread (windows_thread_info *th,
}
th->resume ();
- th->stopping = false;
+ th->stopping = SK_NOT_STOPPING;
th->last_sig = GDB_SIGNAL_0;
}
@@ -1683,8 +1690,19 @@ windows_nat_target::windows_continue (DWORD continue_status, int id,
#endif
}
- if (!target_is_non_stop_p ()
- || (cont_flags & WCONT_CONTINUE_DEBUG_EVENT) != 0)
+ /* WCONT_DONT_CONTINUE_DEBUG_EVENT and WCONT_CONTINUE_DEBUG_EVENT
+ can't both be enabled at the same time. */
+ gdb_assert ((cont_flags & WCONT_DONT_CONTINUE_DEBUG_EVENT) == 0
+ || (cont_flags & WCONT_CONTINUE_DEBUG_EVENT) == 0);
+
+ bool continue_debug_event;
+ if ((cont_flags & WCONT_CONTINUE_DEBUG_EVENT) != 0)
+ continue_debug_event = true;
+ else if ((cont_flags & WCONT_DONT_CONTINUE_DEBUG_EVENT) != 0)
+ continue_debug_event = false;
+ else
+ continue_debug_event = !target_is_non_stop_p ();
+ if (continue_debug_event)
{
DEBUG_EVENTS ("windows_continue -> continue_last_debug_event");
continue_last_debug_event_main_thread
@@ -1879,11 +1897,13 @@ windows_nat_target::interrupt ()
"Press Ctrl-c in the program console."));
}
-/* Stop thread TH. This leaves a GDB_SIGNAL_0 pending in the thread,
- which is later consumed by windows_nat_target::wait. */
+/* Stop thread TH, for STOPPING_KIND reason. This leaves a
+ GDB_SIGNAL_0 pending in the thread, which is later consumed by
+ windows_nat_target::wait. */
void
-windows_nat_target::stop_one_thread (windows_thread_info *th)
+windows_nat_target::stop_one_thread (windows_thread_info *th,
+ enum stopping_kind stopping_kind)
{
ptid_t thr_ptid (windows_process.process_id, th->tid);
@@ -1899,12 +1919,18 @@ windows_nat_target::stop_one_thread (windows_thread_info *th)
#ifdef __CYGWIN__
else if (th->suspended
&& th->signaled_thread != nullptr
- && th->pending_status.kind () == TARGET_WAITKIND_IGNORE)
+ && th->pending_status.kind () == TARGET_WAITKIND_IGNORE
+ /* If doing an internal stop to update debug registers,
+ then just leave the "sig" thread suspended. Otherwise
+ windows_nat_target::wait would incorrectly break the
+ signaled_thread lock when it later processes the pending
+ stop and calls windows_continue on this thread. */
+ && stopping_kind == SK_EXTERNAL)
{
DEBUG_EVENTS ("explict stop for \"sig\" thread %s held for signal",
thr_ptid.to_string ().c_str ());
- th->stopping = true;
+ th->stopping = stopping_kind;
th->pending_status.set_stopped (GDB_SIGNAL_0);
th->last_event = {};
serial_event_set (m_wait_event);
@@ -1918,7 +1944,9 @@ windows_nat_target::stop_one_thread (windows_thread_info *th)
thr_ptid.to_string ().c_str (),
th->suspended, th->stopping);
- th->stopping = true;
+ /* Upgrade stopping. */
+ if (stopping_kind > th->stopping)
+ th->stopping = stopping_kind;
}
else
{
@@ -1927,9 +1955,13 @@ windows_nat_target::stop_one_thread (windows_thread_info *th)
th->suspend ();
gdb_assert (th->suspended);
- th->stopping = true;
- th->pending_status.set_stopped (GDB_SIGNAL_0);
- th->last_event = {};
+ if (stopping_kind > th->stopping)
+ {
+ th->stopping = stopping_kind;
+ th->pending_status.set_stopped (GDB_SIGNAL_0);
+ th->last_event = {};
+ }
+
serial_event_set (m_wait_event);
}
}
@@ -1943,7 +1975,7 @@ windows_nat_target::stop (ptid_t ptid)
{
ptid_t thr_ptid (windows_process.process_id, th->tid);
if (thr_ptid.matches (ptid))
- stop_one_thread (th.get ());
+ stop_one_thread (th.get (), SK_EXTERNAL);
}
}
@@ -2370,6 +2402,17 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
{
windows_thread_info *th = windows_process.find_thread (result);
+ /* If this thread was temporarily stopped just so we
+ could update its debug registers on the next
+ resumption, do it now. */
+ if (th->stopping == SK_INTERNAL)
+ {
+ gdb_assert (fake);
+ windows_continue (DBG_CONTINUE, th->tid,
+ WCONT_DONT_CONTINUE_DEBUG_EVENT);
+ continue;
+ }
+
th->stopped_at_software_breakpoint = false;
if (current_event.dwDebugEventCode
== EXCEPTION_DEBUG_EVENT
@@ -2422,7 +2465,7 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
for (auto &thr : windows_process.thread_list)
thr->suspend ();
- th->stopping = false;
+ th->stopping = SK_NOT_STOPPING;
}
/* If something came out, assume there may be more. This is
@@ -3905,6 +3948,41 @@ Use \"file\" or \"dll\" command to load executable/libraries directly."));
}
}
+/* For each thread, set the debug_registers_changed flag, and
+ temporarily stop it so we can update its debug registers. */
+
+void
+windows_nat_target::debug_registers_changed_all_threads ()
+{
+ for (auto &th : windows_process.thread_list)
+ {
+ th->debug_registers_changed = true;
+
+ /* Note we don't SuspendThread => update debug regs =>
+ ResumeThread, because SuspendThread is actually asynchronous
+ (and GetThreadContext blocks until the thread really
+ suspends), and doing that for all threads may take a bit.
+ Also, the core does one call per DR register update, so that
+ would result in a lot of suspend-resumes. So instead, we
+ suspend the thread if it wasn't already suspended, and queue
+ a pending stop to be handled by windows_nat_target::wait.
+ This means we only stop each thread once, and, we don't block
+ waiting for each individual thread stop. */
+ stop_one_thread (th.get (), SK_INTERNAL);
+ }
+}
+
+/* Trampoline helper to get at the
+ windows_nat_target::debug_registers_changed_all_threads method in
+ the native target. */
+
+static void
+debug_registers_changed_all_threads ()
+{
+ auto *win_tgt = static_cast<windows_nat_target *> (get_native_target ());
+ win_tgt->debug_registers_changed_all_threads ();
+}
+
/* Hardware watchpoint support, adapted from go32-nat.c code. */
/* Pass the address ADDR to the inferior in the I'th debug register.
@@ -3916,8 +3994,7 @@ windows_set_dr (int i, CORE_ADDR addr)
if (i < 0 || i > 3)
internal_error (_("Invalid register %d in windows_set_dr.\n"), i);
- for (auto &th : windows_process.thread_list)
- th->debug_registers_changed = true;
+ debug_registers_changed_all_threads ();
}
/* Pass the value VAL to the inferior in the DR7 debug control
@@ -3926,8 +4003,7 @@ windows_set_dr (int i, CORE_ADDR addr)
static void
windows_set_dr7 (unsigned long val)
{
- for (auto &th : windows_process.thread_list)
- th->debug_registers_changed = true;
+ debug_registers_changed_all_threads ();
}
/* Get the value of debug register I from the inferior. */