[pushed 21/28] Windows gdb+gdbserver: Make siginfo_er per-thread state

[Pedro Alves <pedro@palves.net>]

With non-stop mode support, each thread has its own "last event", and
so printing $_siginfo should print the siginfo of the selected thread.
Likewise, with all-stop and scheduler-locking.

This patch reworks the siginfo functions in gdb/windows-nat.c and
gdbserver/win32-low.cc to reuse the exception record already saved
within each thread's 'last_event' field.

Here's an example of what you'll see after the whole non-stop series:

  (gdb) thread apply all p -pretty -- $_siginfo

  Thread 3 (Thread 2612.0x1470):
  $1 = {
    ExceptionCode = DBG_CONTROL_C,
    ExceptionFlags = 0,
    ExceptionRecord = 0x0,
    ExceptionAddress = 0x7ffd0583e929 <KERNELBASE!EncodeRemotePointer+8249>,
    NumberParameters = 0,
    {
      ExceptionInformation = {0 <repeats 15 times>},
      AccessViolationInformation = {
	Type = READ_ACCESS_VIOLATION,
	Address = 0x0
      }
    }
  }

  Thread 2 (Thread 2612.0x1704):
  $2 = {
    ExceptionCode = SINGLE_STEP,
    ExceptionFlags = 0,
    ExceptionRecord = 0x0,
    ExceptionAddress = 0x7ffd080ad6e4 <ntdll!ZwDelayExecution+20>,
    NumberParameters = 0,
    {
      ExceptionInformation = {0 <repeats 15 times>},
      AccessViolationInformation = {
	Type = READ_ACCESS_VIOLATION,
	Address = 0x0
      }
    }
  }

  Thread 1 (Thread 2612.0x434):
  $3 = {
    ExceptionCode = BREAKPOINT,
    ExceptionFlags = 0,
    ExceptionRecord = 0x0,
    ExceptionAddress = 0x7ff6f691174c <main+185>,
    NumberParameters = 1,
    {
      ExceptionInformation = {0 <repeats 15 times>},
      AccessViolationInformation = {
	Type = READ_ACCESS_VIOLATION,
	Address = 0x0
      }
    }
  }
  (gdb)

This was in non-stop mode, and the program originally had two threads.
Thread 1 stopped for a breakpoint, then thread 2 was manually
interrupted/paused and then single-stepped.  And then I typed Ctrl-C
in the inferior's terminal, which made Windows inject thread 3 in the
inferior, and report a DBG_CONTROL_C exception for it.

Approved-By: Tom Tromey <tom@tromey.com>
Change-Id: I5d4f1b62f59e8aef3606642c6524df2362b0fb7d
commit-id:e0f75dea
---
 gdb/nat/windows-nat.c  |  2 --
 gdb/nat/windows-nat.h  |  3 ---
 gdb/windows-nat.c      | 33 ++++++++++++++++-----------------
 gdbserver/win32-low.cc | 27 ++++++++++++++-------------
 4 files changed, 30 insertions(+), 35 deletions(-)

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index 7eff99170fc..1f8967dcd8d 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -357,8 +357,6 @@ windows_process_info::handle_exception (DEBUG_EVENT &current_event,
   DWORD code = rec->ExceptionCode;
   handle_exception_result result = HANDLE_EXCEPTION_HANDLED;
 
-  memcpy (&siginfo_er, rec, sizeof siginfo_er);
-
   switch (code)
     {
     case EXCEPTION_ACCESS_VIOLATION:
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index 8555085c9f7..152410580f0 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -152,9 +152,6 @@ struct windows_process_info
   DWORD process_id = 0;
   DWORD main_thread_id = 0;
 
-  /* Contents of $_siginfo */
-  EXCEPTION_RECORD siginfo_er {};
-
 #ifdef __x86_64__
   /* The target is a WOW64 process */
   bool wow64_process = false;
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index b5e80139c26..1593524f900 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -2336,7 +2336,6 @@ windows_nat_target::mourn_inferior ()
       CHECK (CloseHandle (windows_process->handle));
       windows_process->open_process_used = 0;
     }
-  windows_process->siginfo_er.ExceptionCode = 0;
   inf_child_target::mourn_inferior ();
 }
 
@@ -2453,8 +2452,15 @@ static enum target_xfer_status
 windows_xfer_siginfo (gdb_byte *readbuf, ULONGEST offset, ULONGEST len,
 		      ULONGEST *xfered_len)
 {
-  char *buf = (char *) &windows_process->siginfo_er;
-  size_t bufsize = sizeof (windows_process->siginfo_er);
+  windows_thread_info *th = windows_process->find_thread (inferior_ptid);
+
+  if (th->last_event.dwDebugEventCode != EXCEPTION_DEBUG_EVENT)
+    return TARGET_XFER_E_IO;
+
+  EXCEPTION_RECORD &er = th->last_event.u.Exception.ExceptionRecord;
+
+  char *buf = (char *) &er;
+  size_t bufsize = sizeof (er);
 
 #ifdef __x86_64__
   EXCEPTION_RECORD32 er32;
@@ -2463,23 +2469,16 @@ windows_xfer_siginfo (gdb_byte *readbuf, ULONGEST offset, ULONGEST len,
       buf = (char *) &er32;
       bufsize = sizeof (er32);
 
-      er32.ExceptionCode = windows_process->siginfo_er.ExceptionCode;
-      er32.ExceptionFlags = windows_process->siginfo_er.ExceptionFlags;
-      er32.ExceptionRecord
-	= (uintptr_t) windows_process->siginfo_er.ExceptionRecord;
-      er32.ExceptionAddress
-	= (uintptr_t) windows_process->siginfo_er.ExceptionAddress;
-      er32.NumberParameters = windows_process->siginfo_er.NumberParameters;
-      int i;
-      for (i = 0; i < EXCEPTION_MAXIMUM_PARAMETERS; i++)
-	er32.ExceptionInformation[i]
-	  = windows_process->siginfo_er.ExceptionInformation[i];
+      er32.ExceptionCode = er.ExceptionCode;
+      er32.ExceptionFlags = er.ExceptionFlags;
+      er32.ExceptionRecord = (uintptr_t) er.ExceptionRecord;
+      er32.ExceptionAddress = (uintptr_t) er.ExceptionAddress;
+      er32.NumberParameters = er.NumberParameters;
+      for (int i = 0; i < EXCEPTION_MAXIMUM_PARAMETERS; i++)
+	er32.ExceptionInformation[i] = er.ExceptionInformation[i];
     }
 #endif
 
-  if (windows_process->siginfo_er.ExceptionCode == 0)
-    return TARGET_XFER_E_IO;
-
   if (readbuf == nullptr)
     return TARGET_XFER_E_IO;
 
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index 5e09779082c..cc4a63319ef 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -643,7 +643,6 @@ win32_clear_process ()
     }
 
   for_each_thread (delete_thread_info);
-  windows_process.siginfo_er.ExceptionCode = 0;
 }
 
 /* Implementation of target_ops::kill.  */
@@ -1271,14 +1270,18 @@ win32_process_target::qxfer_siginfo (const char *annex,
 				     unsigned const char *writebuf,
 				     CORE_ADDR offset, int len)
 {
-  if (windows_process.siginfo_er.ExceptionCode == 0)
+  windows_thread_info *th = windows_process.find_thread (current_thread->id);
+
+  if (th->last_event.dwDebugEventCode != EXCEPTION_DEBUG_EVENT)
     return -1;
 
   if (readbuf == nullptr)
     return -1;
 
-  char *buf = (char *) &windows_process.siginfo_er;
-  size_t bufsize = sizeof (windows_process.siginfo_er);
+  EXCEPTION_RECORD &er = th->last_event.u.Exception.ExceptionRecord;
+
+  char *buf = (char *) &er;
+  size_t bufsize = sizeof (er);
 
 #ifdef __x86_64__
   EXCEPTION_RECORD32 er32;
@@ -1287,17 +1290,15 @@ win32_process_target::qxfer_siginfo (const char *annex,
       buf = (char *) &er32;
       bufsize = sizeof (er32);
 
-      er32.ExceptionCode = windows_process.siginfo_er.ExceptionCode;
-      er32.ExceptionFlags = windows_process.siginfo_er.ExceptionFlags;
+      er32.ExceptionCode = er.ExceptionCode;
+      er32.ExceptionFlags = er.ExceptionFlags;
       er32.ExceptionRecord
-	= (uintptr_t) windows_process.siginfo_er.ExceptionRecord;
+	= (uintptr_t) er.ExceptionRecord;
       er32.ExceptionAddress
-	= (uintptr_t) windows_process.siginfo_er.ExceptionAddress;
-      er32.NumberParameters = windows_process.siginfo_er.NumberParameters;
-      int i;
-      for (i = 0; i < EXCEPTION_MAXIMUM_PARAMETERS; i++)
-	er32.ExceptionInformation[i]
-	  = windows_process.siginfo_er.ExceptionInformation[i];
+	= (uintptr_t) er.ExceptionAddress;
+      er32.NumberParameters = er.NumberParameters;
+      for (int i = 0; i < EXCEPTION_MAXIMUM_PARAMETERS; i++)
+	er32.ExceptionInformation[i] = er.ExceptionInformation[i];
     }
 #endif
 
-- 
2.53.0