Re: [PATCH] gdb: only include mips and riscv targets if building with 64-bit bfd

[Andrew Burgess <aburgess@redhat.com>]

Thank you everyone for all the feedback.

I've now pushed this patch.  As has been discussed on this thread, and
the thread Jim linked, if/when the situation changes, and either riscv
or mips can build with a 32-bit libbfd, then I'm obviously happy for
some/all of this patch to be reverted.

Thanks,
Andrew


* Andrew Burgess <aburgess@redhat.com> [2021-12-09 18:08:26 +0000]:

> While testing another patch I was trying to build different
> configurations of GDB, and, during one test build I ran into a
> problem, I configured with `--enable-targets=all
> --host=i686-w64-mingw32` and saw this error while linking GDB:
> 
>   .../i686-w64-mingw32/bin/ld: mips-tdep.o: in function `mips_gdbarch_init':
>   .../src/gdb/mips-tdep.c:8730: undefined reference to `disassembler_options_mips'
>   .../i686-w64-mingw32/bin/ld: riscv-tdep.o: in function `riscv_gdbarch_init':
>   .../src/gdb/riscv-tdep.c:3851: undefined reference to `disassembler_options_riscv'
> 
> So the `disassembler_options_mips` and `disassembler_options_riscv`
> symbols are missing.
> 
> This turns out to be because mips-dis.c and riscv-dis.c, in which
> these symbols are defined, are in the TARGET64_LIBOPCODES_CFILES list
> in opcodes/Makefile.am, these files are only built when we are
> building with a 64-bit bfd.
> 
> If we look further, into bfd/Makefile.am, we can see that all the
> files matching elf*-riscv.lo are in the BFD64_BACKENDS list, as are
> the elf*-mips.lo files, and (I know because I tried), the two
> disassemblers do, not surprisingly, depend on features supplied from
> libbfd.
> 
> So, though we can build most of GDB just fine for riscv and mips with
> a 32-bit bfd, if I understand correctly, the final GDB
> executable (assuming we could get it to link) would not understand
> these architectures at the bfd level, nor would there be any
> disassembler available.  This sounds like a pretty useless GDB to me.
> 
> So, in this commit, I move the riscv and mips targets into GDB's list
> of targets that require a 64-bit bfd.  After this I can build GDB just
> fine with the configure options given above.
> ---
>  gdb/Makefile.in | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/gdb/Makefile.in b/gdb/Makefile.in
> index bff27577b95..f2966cf6c00 100644
> --- a/gdb/Makefile.in
> +++ b/gdb/Makefile.in
> @@ -710,10 +710,21 @@ ALL_64_TARGET_OBS = \
>  	arch/aarch64-insn.o \
>  	arch/aarch64-mte-linux.o \
>  	arch/amd64.o \
> +	arch/riscv.o \
>  	ia64-linux-tdep.o \
>  	ia64-tdep.o \
>  	ia64-vms-tdep.o \
> +	mips-fbsd-tdep.o \
> +	mips-linux-tdep.o \
> +	mips-netbsd-tdep.o \
> +	mips-sde-tdep.o \
> +	mips-tdep.o \
>  	mips64-obsd-tdep.o \
> +	riscv-fbsd-tdep.o \
> +	riscv-linux-tdep.o \
> +	riscv-none-tdep.o \
> +	riscv-ravenscar-thread.o \
> +	riscv-tdep.o \
>  	sparc64-fbsd-tdep.o \
>  	sparc64-linux-tdep.o \
>  	sparc64-netbsd-tdep.o \
> @@ -734,7 +745,6 @@ ALL_TARGET_OBS = \
>  	arch/arm-linux.o \
>  	arch/i386.o \
>  	arch/ppc-linux-common.o \
> -	arch/riscv.o \
>  	arm-bsd-tdep.o \
>  	arm-fbsd-tdep.o \
>  	arm-linux-tdep.o \
> @@ -793,11 +803,6 @@ ALL_TARGET_OBS = \
>  	mep-tdep.o \
>  	microblaze-linux-tdep.o \
>  	microblaze-tdep.o \
> -	mips-fbsd-tdep.o \
> -	mips-linux-tdep.o \
> -	mips-netbsd-tdep.o \
> -	mips-sde-tdep.o \
> -	mips-tdep.o \
>  	mn10300-linux-tdep.o \
>  	mn10300-tdep.o \
>  	moxie-tdep.o \
> @@ -818,11 +823,6 @@ ALL_TARGET_OBS = \
>  	ppc-sysv-tdep.o \
>  	ppc64-tdep.o \
>  	ravenscar-thread.o \
> -	riscv-fbsd-tdep.o \
> -	riscv-linux-tdep.o \
> -	riscv-none-tdep.o \
> -	riscv-ravenscar-thread.o \
> -	riscv-tdep.o \
>  	rl78-tdep.o \
>  	rs6000-aix-tdep.o \
>  	rs6000-lynx178-tdep.o \
> -- 
> 2.25.4
>