Re: the redirected stdin/out/err for new console is wrong when the gdb's stdin/out/err is already redirected

[Eli Zaretskii via Gdb-patches <gdb-patches@sourceware.org>]

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> From: Roy Qu <royqh1979@gmail.com>
> Date: Tue, 29 Sep 2020 07:48:18 +0800
> 
> Yes, (HANLDE)0 is the same as NULL. 
> 
> These code will get running when we want to run/start the inferior  and at least one of inferior's
> STDIN/STDOUT/STDERR is to be redirected.  
>    si.hStdInput / si.hStdOutput/ si.hStdError are the handle for STDIN/STDOUT/STDERR you want the child
> process ( console window) to use.    
> 
> Let's the following old code for the STDOUT:
> 
>       if (fd_out >= 0)
> si.hStdOutput = (HANDLE) _get_osfhandle (fd_out);
>       else if (tty != INVALID_HANDLE_VALUE)
> si.hStdOutput = tty;
>       else
> si.hStdOutput =  GetStdHandle (STD_OUTPUT_HANDLE)  ;
> 
> If the inferior process's STDOUT is to be redirected,  fd_out will be a valid file_descriptor (>0) to the
> redirected source, and  _get_osfhandle will
> get its corresponding windows handle.
> If the STDOUT is not to be redirected (else if)   , tty is from get_inferior_io_terminal(), which should the
> inferior's current  tty's handle; (I'm not sure
> if here is correct, because STDIN/STDOUT/STDERR should be 3 HANDLEs， but here we use the same
> one）
> If the STDOUT is not to be redirected and we don't have a valid tty already (else ), then we should let the
> inferior use new console STDOUT ( output to the screen).
> 
> But here the following old code is wrong:
> si.hStdOutput =  GetStdHandle (STD_OUTPUT_HANDLE)  ; 
> It tries to fetch the main gdb's currrent STDOUT handle and let the inferior to use it. If the main gdb's
> STDOUT is not redirected, that's ok.
> If the main gdb's STDOUT is already redirected, this will get the inferior's STDOUT redirected too, that's
> wrong.
> 
> the new code:
>   si.hStdOutput = NULL;
> will let inferior's STDOUT use the console's default output handle (output to its console's screen). That's
> what we want.
> 
> Logic of the code for STDIN/STDERR is the same.That's ALL

Thanks.

My hesitation is that I don't see the significance of NULL as the
standard handle documented in the MS docs of CreateProcess.  What am I
missing there?

Another potential issue is whether, when GDB's standard output was
redirected, we might want stdout of the inferior to be redirected to
the same file/device.  In your case, that is definitely not so, but I
wonder if there are other use cases where the desired behavior could
be different?  Running the test suite, perhaps?