Re: [PATCH 4/5] Fix exit/signal code on Cygwin

[Eli Zaretskii <eliz@gnu.org>]

> From: Pedro Alves <pedro@palves.net>
> Date: Fri, 22 May 2026 01:16:25 +0100
> 
> I noticed that on native Cygwin, gdb.python/py-events.exp has this:
> 
>  [Thread 15952.0x534 (id 1) exited with code 12]
> ...
>  Program terminated with signal SIGSYS, Bad system call.
>  ...
>  (gdb) FAIL: gdb.python/py-events.exp: Inferior 1 terminated.
> 
> The program exits with normal exit code 12, not a signal.  SIGSYS is
> 12.
> 
> Similarly, gdb.base/exitsignal.exp has this:
> 
>  continue
>  Continuing.
>  [Thread 15220.0x219c (id 1) exited with code 2816]
>  [Thread 15220.0x3a50 (id 3) exited with code 2816]
>  [Thread 15220.0x25a0 (id 4) exited with code 2816]
>  [Inferior 1 (process 15220) exited with code 05400]
>  (gdb) FAIL: gdb.base/exitsignal.exp: program terminated with SIGSEGV (the program exited)
> 
> Here, the program exits with SIGSEGV, not normal exit code 2816 (05400
> in octal).
> 
> The problem is that gdb/windows-nat.c does not know about Cygwin's
> exit codes as seen from the native Windows side.  Same for gdbserver's
> win32-low.c.
> 
> This commit fixes it.  To avoid duplicating code, it adds a new
> native_exit_code_to_target_status function in nat/windows-nat.c used
> by both GDB and GDBserver, with the MinGW-specific logic added by
> commit 559e7e5056 ("Improve process exit status macros on MinGW")
> moved there too.

AFAIU, this basically adds a Cygwin-specific branch to the code that
determines the terminating signal and status of a program, leaving the
code for the native Windows and MinGW programs intact.  I suggest to
say this in the commit log message, because as written, it sounds like
it does something for Cygwin that is not done for MinGW.  Which is not
true.

> +#ifdef __CYGWIN__
> +  /* /usr/include/cygwin/wait.h explains that a wait status is 16
> +     bits, and looks like:
> +
> +       "<1 byte info> <1 byte code>
> +       <code> == 0, child has exited, info is the exit value
> +       <code> == 1..7e, child has exited, code is the signal number.
> +       <code> == 7f, child has stopped, info was the signal number.
> +       <code> == 80, there was a core dump."
> +
> +     However, when passing the wait status to native ExitProcess as a
> +     native exit code, cygwin1.dll swaps the <info>/<code> bytes.
> +     Swap them back into a wait status here.  */
> +  int wstatus = ((exit_code & 0xff) << 8) | ((exit_code >> 8) & 0xff);

Should the commentary say something about _why_ we swap the bytes
here?  I know very little about Cygwin, but my naïve view is that when
a Cygwin program is run from another Cygwin program, no such swapping
should be needed, is that right?  One should just use the macros from
the sys/wait.h header, right?  If so, why do we need to swap the bytes
here, and how is "passing the wait status to native ExitProcess as a
native exit code" relevant to what this part of GDB needs to do?

Other than these questions, the MinGW part of the code looks okay to
me, thanks.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>