[newlib-cygwin/main] Cygwin: Don't terminate via dumper

[Jon Turney <jturney@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=15140d6df667a71e660dc9da9ca9071fa3c5dbbd

commit 15140d6df667a71e660dc9da9ca9071fa3c5dbbd
Author: Jon Turney <jon.turney@dronecode.org.uk>
Date:   Tue Jan 16 16:12:51 2024 +0000

    Cygwin: Don't terminate via dumper
    
    A process which is exiting due to a core dumping signal doesn't
    propagate the correct exist status after dumping core, because 'dumper'
    itself forcibly terminates the process.
    
    Use 'dumper -n' to avoid killing the dumped process, so we continue to
    the end of signal_exit(), to exit with the 128+signal exit status.
    
    Busy-wait in exec_prepared_command() in an attempt to reliably notice
    the dumper attaching, so we don't get stuck there.
    
    Also: document these important facts for custom uses of error_start.

Diff:
---
 winsup/cygwin/exceptions.cc | 7 +++----
 winsup/doc/cygwinenv.xml    | 6 ++++++
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/exceptions.cc b/winsup/cygwin/exceptions.cc
index 8b1c5493e..0e1a804ca 100644
--- a/winsup/cygwin/exceptions.cc
+++ b/winsup/cygwin/exceptions.cc
@@ -149,7 +149,7 @@ dumper_init (void)
 
   /* Calculate the length of the command, allowing for an appended DWORD PID and
      terminating null */
-  int cmd_len = 1 + wcslen(dll_dir) + 11 + 2 + 1 + wcslen(global_progname) + 1 + 10 + 1;
+  int cmd_len = 1 + wcslen(dll_dir) + 11 + 5 + 1 + wcslen(global_progname) + 1 + 10 + 1;
   if (cmd_len > 32767)
     {
       /* If this comes to more than the 32,767 characters CreateProcess() can
@@ -163,7 +163,7 @@ dumper_init (void)
   cp = wcpcpy (cp, L"\"");
   cp = wcpcpy (cp, dll_dir);
   cp = wcpcpy (cp, L"\\dumper.exe");
-  cp = wcpcpy (cp, L"\" ");
+  cp = wcpcpy (cp, L"\" -n ");
   cp = wcpcpy (cp, L"\"");
   cp = wcpcpy (cp, global_progname);
   wcscat (cp, L"\"");
@@ -570,9 +570,8 @@ int exec_prepared_command (PWCHAR command)
     system_printf ("Failed to start, %E");
   else
     {
-      SetThreadPriority (GetCurrentThread (), THREAD_PRIORITY_IDLE);
       while (!being_debugged ())
-	Sleep (1);
+	Sleep (0);
       Sleep (2000);
     }
 
diff --git a/winsup/doc/cygwinenv.xml b/winsup/doc/cygwinenv.xml
index d97f2b77d..05672c404 100644
--- a/winsup/doc/cygwinenv.xml
+++ b/winsup/doc/cygwinenv.xml
@@ -46,6 +46,12 @@ to the command as arguments.
   Note: This has no effect if a debugger is already attached when the fatal
   error occurs.
 </para>
+<para>
+  Note: The command invoked must either (i) attach to the errored process with
+  <function>DebugActiveProcess()</function>, or (ii) forcibly terminate the
+  errored process (with <function>TerminateProcess()</function> or similar), as
+  otherwise the errored process will wait forever for a debugger to attach.
+</para>
 </listitem>
 
 <listitem>