Re: Building today's snapshot of GDB with MinGW

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2020-07-02 9:50 a.m., Eli Zaretskii wrote:
>> Date: Wed, 01 Jul 2020 18:09:11 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> Cc: gdb-patches@sourceware.org, brobecker@adacore.com, tromey@adacore.com
>>
>>> We would not expect GDB to complain for Windows on i386:x86-64.
>>>
>>> The first thing I would do is make sure that the function _initialize_amd64_windows_tdep
>>> gets executed at startup in your GDB.  This is the function that registers a handler for
>>> the tuple (i386:x86-64, Windows).
>>
>> Thanks, I will take a look there and report what I see.
> 
> I started looking at the code, but then I had a eureka moment.  You
> mentioned _initialize_amd64_windows_tdep, so I presume you assumed my
> build is a 64-bit one?  It isn't: it's a 3--bit build, and thus
> _initialize_amd64_windows_tdep is not even compiled into the binary.
> 
> Given that my build is a 32-bit one, it sounds expected to see
> warnings I cited, as they all complain about 64-bit architectures,
> right?
> 
> Incidentally, I wonder why the gdbarch selftest is trying
> architectures that are not supported and not even compiled in.  What
> is the purpose of doing that?

It loops over all the architectures known to bfd.  So I suppose that in BFD,
enabling support for i386 enables support for x86-64, that it all comes
together.  But in GDB, when configuring GDB for a Windows i386 target, we
don't add support for Windows x86-64 targets.  So the warnings you see make
sense.

I noticed that when configuring GDB for an i386/Linux target, we also throw
in support for amd64/Linux as well if $enable_64_bit_bfd is true (which allows
a 32-bit program to read a large > 4GB executable, I suppose):

290 i[34567]86-*-linux*)
291         # Target: Intel 386 running GNU/Linux
292         gdb_target_obs="i386-linux-tdep.o \
293                         glibc-tdep.o \
294                         solib-svr4.o symfile-mem.o \
295                         linux-tdep.o linux-record.o"
296         if test "x$enable_64_bit_bfd" = "xyes"; then
297             # Target: GNU/Linux x86-64
298             gdb_target_obs="amd64-linux-tdep.o ${gdb_target_obs}"
299         fi
300         ;;

We could perhaps do the same for Windows, I don't think there would be any
downsides to it, and it could be useful to some people.

Simon