Re: [RFAv3 2/6] Improve process exit status macros on MinGW

[Pedro Alves <palves@redhat.com>]

On 12/17/19 4:59 PM, Eli Zaretskii wrote:
>> From: Pedro Alves <palves@redhat.com>
>> Date: Mon, 27 May 2019 18:33:11 +0100
> 
> To recap, back in May Philippe added the 'pipe' command, and we had a
> brief discussion regarding the use of WIFEXITED, WIFSIGNALED, and
> other related macros from <sys/wait.h>, on MS-Windows.  It was decided
> back then to leave for later the translation of exit codes returned by
> 'pipe' in MS-Windows build of GDB.
> 
> I've now started to look at this issue, with the intent to provide ext
> status to signal conversion for the MS-Windows ports of GDB, and I
> have a few questions regarding the details.
> 
> In that discussion, Pedro commented on Philippe's proposed patch
> (https://sourceware.org/ml/gdb-patches/2019-05/msg00131.html) which
> added the definitions for WIF* and WEXIT* macros to gdb_wait.h and
> their use in widnows-nat.c.  The comments are in
> https://sourceware.org/ml/gdb-patches/2019-05/msg00590.html, and go
> like this:
> 
>>> 	* common/gdb_wait.h (WIFEXITED, WIFSIGNALED, WEXITSTATUS,
>>> 	WTERMSIG): Define better versions for MinGW.
>>> 	* windows-nat.c (xlate): Uncomment the definition.
>>> 	(windows_status_to_termsig): New function.
>>
>> windows-nat.c looks like the wrong place to put this.
>>
>> windows-nat.c is only included in the build if building a native
>> debugger.  But, you need this functionality on every Windows-hosted build
>> of GDB, even cross debuggers.  So I think you're breaking the build on
>> the Windows-hosted, non-native-debugger case.
>>
>> E.g., --host=mingw --target=arm-none-eabi.
>>
>> The right place would be mingw-hdep.c.
> 
> I'm okay with doing this in mingw-hdep.c, but I'm a bit confused by
> this comment.  The encoding of the fatal exception in the exit status
> of a program is a feature of the native MS-Windows processes.  Does
> "running cross-debugger" mentioned above allude to running an
> MS-Windows program?  

The issue pointed out was that by putting the windows_status_to_termsig
function in windows-nat.c, and then calling it from gdb's common code
(cli/cli-cmds.c, via WTERMSIG) would result in a build/link failure when
you try to build a cross debugger hosted on mingw, because such a gdb
build does not include the native Windows target support, i.e., does not
build/link the windows-nat.o object.  Putting said function in mingw-hdep.c
instead fixes that issue because that file is included as part of the build
in all kinds of mingw-hosted GDBs, either native or cross-debugger.

>> I admit to being a bit confused about why we want to do this
>> translation for this feature while we don't do it for the exit code
>> of inferiors running under gdb, for example.  I mean, exit status
>> with 0xc0000000 set don't cause $_exitsignal to be set instead of
>> $_exitcode.
> 
> Yes, we should do this for exit code of inferiors as well.
> 
> Native MS-Windows debugging produces the TARGET_WAITKIND_* values in
> windows-nat.c, so I think the conversion we are talking about will
> have to be done there, perhaps _in_addition_to_ other places?  IOW,
> the function that performs the conversion can be defined in
> mingw-hdep.c, but it will have to be called from windows-nat.c at
> least, right?  And I'm uncertain what other places will have to call
> that conversion function for the use case of running a cross-debugger,
> can someone please help me understand that?

You'll also want to call it in gdbserver's win32-low.c file, so that
you get the translation too when debugging against gdbserver.
This actually suggests putting the new function in some new
shared file in gdb/gdbsupport/, since gdb/mingw-hdep.c is gdb-only.

Thanks,
Pedro Alves