[binutils-gdb] Fix regression on Windows with WOW64

[Tom Tromey <tromey@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7ae6857316e020467f84645ba7c1c5ec6c085bd9

commit 7ae6857316e020467f84645ba7c1c5ec6c085bd9
Author: Tom Tromey <tromey@adacore.com>
Date:   Thu Mar 31 07:55:09 2022 -0600

    Fix regression on Windows with WOW64
    
    Internally at AdaCore, we recently started testing a 64-bit gdb
    debugging 32-bit processes.  This failed with gdb head, but not with
    gdb 11.
    
    The tests fail like this:
    
         Starting program: [...].exe
         warning: Could not load shared library symbols for WOW64_IMAGE_SECTION.
         Do you need "set solib-search-path" or "set sysroot"?
         warning: Could not load shared library symbols for WOW64_IMAGE_SECTION.
         Do you need "set solib-search-path" or "set sysroot"?
         warning: Could not load shared library symbols for NOT_AN_IMAGE.
         Do you need "set solib-search-path" or "set sysroot"?
         warning: Could not load shared library symbols for NOT_AN_IMAGE.
         Do you need "set solib-search-path" or "set sysroot"?
    
    After some debugging and bisecting, to my surprise the bug was
    introduced by commit 183be222 ("gdb, gdbserver: make target_waitstatus
    safe").
    
    The problem occurs in handle_exception.  Previously the code did:
    
        -  ourstatus->kind = TARGET_WAITKIND_STOPPED;
        [...]
             case EXCEPTION_BREAKPOINT:
        [...]
        -     ourstatus->kind = TARGET_WAITKIND_SPURIOUS;
        [...]
               /* FALLTHROUGH */
             case STATUS_WX86_BREAKPOINT:
               DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
        -      ourstatus->value.sig = GDB_SIGNAL_TRAP;
        [...]
        -  last_sig = ourstatus->value.sig;
    
    However, in the new code, the fallthrough case does:
    
        +      ourstatus->set_stopped (GDB_SIGNAL_TRAP);
    
    ... which changes the 'kind' in 'ourstatus' after falling through.
    
    This patch rearranges the 'last_sig' setting to more closely match
    what was done before (this is probably not strictly needed but also
    seemed harmless), and removes the fall-through in the
    'ignore_first_breakpoint' case when __x86_64__ is defined.

Diff:
---
 gdb/nat/windows-nat.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index c890ee13c6c..2e4c4826797 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -183,6 +183,8 @@ windows_process_info::handle_exception (struct target_waitstatus *ourstatus,
   thread_rec (ptid_t (current_event.dwProcessId, current_event.dwThreadId, 0),
 	      DONT_SUSPEND);
 
+  last_sig = GDB_SIGNAL_0;
+
   switch (code)
     {
     case EXCEPTION_ACCESS_VIOLATION:
@@ -243,8 +245,10 @@ windows_process_info::handle_exception (struct target_waitstatus *ourstatus,
 	     on startup, first a BREAKPOINT for the 64bit ntdll.dll,
 	     then a WX86_BREAKPOINT for the 32bit ntdll.dll.
 	     Here we only care about the WX86_BREAKPOINT's.  */
+	  DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT - ignore_first_breakpoint");
 	  ourstatus->set_spurious ();
 	  ignore_first_breakpoint = false;
+	  break;
 	}
       else if (wow64_process)
 	{
@@ -255,7 +259,7 @@ windows_process_info::handle_exception (struct target_waitstatus *ourstatus,
 	     gdb lets the target process continue.
 	     So handle it as SIGINT instead, then the target is stopped
 	     unconditionally.  */
-	  DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT");
+	  DEBUG_EXCEPTION_SIMPLE ("EXCEPTION_BREAKPOINT - wow64_process");
 	  rec->ExceptionCode = DBG_CONTROL_C;
 	  ourstatus->set_stopped (GDB_SIGNAL_INT);
 	  break;