[PATCH v2 11/47] Windows gdb+gdbserver: Eliminate thread_rec(INVALIDATE_CONTEXT) calls

Pedro Alves
2025-05-19T13:27:52Z

Replace thread_rec(INVALIDATE_CONTEXT) calls with find_thread, and
invalidate_context / suspend calls in the spots that might need those.

I don't know why does the INVALIDATE_CONTEXT implementation in GDB
avoid suspending the event thread:

case INVALIDATE_CONTEXT:
if (ptid.lwp () != current_event.dwThreadId)
th->suspend ();

Checks for a global "current_event" get in the way of non-stop support
later in the series, as each thread will have its own "last debug
event". Regardless, it should be fine to suspend the event thread.
As a data point, the GDBserver implementation always suspends. So
this patch does not try to avoid suspending the event thread on the
native side either.

Approved-By: Tom Tromey <tom@tromey.com>
Change-Id: I8d2f0a749d23329956e62362a7007189902dddb5
---
gdb/nat/windows-nat.h | 2 --
gdb/windows-nat.c | 23 +++++++++--------------
gdbserver/win32-low.cc | 10 ++++------
3 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 71560930e84..f7f2f3e62a7 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -109,8 +109,6 @@ enum thread_disposition_type
{
/* Invalidate the context, but do not suspend the thread. */
DONT_SUSPEND,
- /* Invalidate the context and suspend the thread. */
- INVALIDATE_CONTEXT
};

/* A single pending stop. See "pending_stops" for more
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 4a10cf962a9..be62d2a6cad 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -541,11 +541,6 @@ windows_per_inferior::thread_rec (ptid_t ptid,
{
switch (disposition)
{
- case INVALIDATE_CONTEXT:
- if (ptid.lwp () != current_event.dwThreadId)
- th->suspend ();
- invalidate_context (th);
- break;
case DONT_SUSPEND:
th->suspended = -1;
invalidate_context (th);
@@ -717,8 +712,7 @@ windows_fetch_one_register (struct regcache *regcache,
void
windows_nat_target::fetch_registers (struct regcache *regcache, int r)
{
- windows_thread_info *th
- = windows_process.thread_rec (regcache->ptid (), INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (regcache->ptid ());

/* Check if TH exists. Windows sometimes uses a non-existent
thread id in its events. */
@@ -729,6 +723,7 @@ windows_nat_target::fetch_registers (struct regcache *regcache, int r)
{
if (context->ContextFlags == 0)
{
+ th->suspend ();
context->ContextFlags = WindowsContext<decltype(context)>::all;
CHECK (get_thread_context (th->h, context));
}
@@ -755,6 +750,7 @@ windows_store_one_register (const struct regcache *regcache,

char *context_ptr = windows_process.with_context (th, [] (auto *context)
{
+ gdb_assert (context->ContextFlags != 0);
return (char *) context;
});

@@ -789,8 +785,7 @@ windows_store_one_register (const struct regcache *regcache,
void
windows_nat_target::store_registers (struct regcache *regcache, int r)
{
- windows_thread_info *th
- = windows_process.thread_rec (regcache->ptid (), INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (regcache->ptid ());

/* Check if TH exists. Windows sometimes uses a non-existent
thread id in its events. */
@@ -1452,7 +1447,9 @@ windows_nat_target::get_windows_debug_event
*ourstatus = stop->status;

ptid_t ptid (windows_process.current_event.dwProcessId, thread_id);
- windows_process.thread_rec (ptid, INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (ptid);
+ if (th != nullptr)
+ windows_process.invalidate_context (th);
return ptid;
}

@@ -1673,8 +1670,7 @@ windows_nat_target::get_windows_debug_event
&& windows_process.windows_initialization_done)
{
ptid_t ptid = ptid_t (current_event->dwProcessId, thread_id, 0);
- windows_thread_info *th
- = windows_process.thread_rec (ptid, INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (ptid);
th->stopped_at_software_breakpoint = true;
th->pc_adjusted = false;
}
@@ -1712,8 +1708,7 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
if (ourstatus->kind () != TARGET_WAITKIND_EXITED
&& ourstatus->kind () != TARGET_WAITKIND_SIGNALLED)
{
- windows_thread_info *th
- = windows_process.thread_rec (result, INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (result);

if (th != nullptr)
{
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index 2bf42f42350..42026971037 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -443,9 +443,8 @@ static void
child_fetch_inferior_registers (struct regcache *regcache, int r)
{
int regno;
- windows_thread_info *th
- = windows_process.thread_rec (current_thread->id,
- INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (current_thread->id);
+ win32_require_context (th);
if (r == -1 || r > NUM_REGS)
child_fetch_inferior_registers (regcache, NUM_REGS);
else
@@ -459,9 +458,8 @@ static void
child_store_inferior_registers (struct regcache *regcache, int r)
{
int regno;
- windows_thread_info *th
- = windows_process.thread_rec (current_thread->id,
- INVALIDATE_CONTEXT);
+ windows_thread_info *th = windows_process.find_thread (current_thread->id);
+ win32_require_context (th);
if (r == -1 || r == 0 || r > NUM_REGS)
child_store_inferior_registers (regcache, NUM_REGS);
else
--
2.49.0