Re: Bug when cross-compiling for ppc

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

On 9/12/23 12:42, Vincent Fortier via Gdb wrote:
> As introduction, I part of SynoCommunity who maintains free software
> packages that can be installed on synology NAS.  Multiple archs are
> supported from armv5, v7, v8, ppc, i686 and x64.  I am able to build
> gdb for all archs with exception of ppc, more specifically qoriq arch
> using gcc-4.9.3 from Synology provided toolchain.
> 
> github PR available here: https://github.com/SynoCommunity/spksrc/pull/5879
> 
> I was finally able to figure out why (now needs to know how to fix it)
> gdb fails to cross-compile for ppc.  I am able to reproduce this
> problem on both gdb-7.12.1 and latest 13.2.
> 
> Basically, when it goes into the configure script under sim/ppc at a
> certain point it tests the "build" c compiler:
> 
> checking for i686-pc-linux-gcc... gcc
> checking whether the C compiler works... no
> configure: error: in
> `/home/spksrc/qoriq-debug/spksrc/cross/gdb-latest/work-qoriq-6.2.4/gdb-13.2/sim/ppc/build.4119280':
> configure: error: C compiler cannot create executables
> See `config.log' for more details
> mv: cannot stat 'config.h': No such file or directory
> 
> The end-result way later on is that build-config.h is then missing:
> 
> fatal error: build-config.h: No such file or directory
>    23 | #include "build-config.h"
>       |          ^~~~~~~~~~~~~~~~
> compilation terminated.
> 
> As at the end of sim/ppc/configure it does a mv config.h
> ../build-config.h but config.h was not generated in the first place.
> 
> What I ended-up doing is commenting out the tmpdir removal from that
> configure script:
> 
>   CFLAGS="${saved_CFLAGS}"
>   mv config.h ../build-config.h
>   cd ..
>   ###rm -rf $tempdir
> 
> Which allowed me to keep track of the real error happening in background:
> 
> configure:2482: checking whether the C compiler works
> configure:2504: gcc -g -O
> -I/home/spksrc/qoriq-debug/spksrc/toolchain/syno-qoriq-6.2.4/work/powerpc-e500v2-linux-gnuspe/powerpc-e500v2-linux-gnuspe/sysroot/usr/include
> -mcpu=8548 -mhard-float -mfloat-gprs=double
> -I/home/spksrc/qoriq-debug/spksrc/cross/gdb-latest/work-qoriq-6.2.4/install/usr/local/gdb/include
>   conftest.c  >&5
> gcc: warning: '-mcpu=' is deprecated; use '-mtune=' or '-march=' instead
> gcc: error: unrecognized command-line option '-mfloat-gprs=double'
> configure:2508: $? = 1
> configure:2546: result: no
> 
> When testing the "build" compiler it includes the "target" flags which
> includes -mcpu=8548 -mhard-float -mfloat-gprs=double. In turns these
> flags should never get used on with "build" compiler making it to
> fail.
> 
> Now the question is, how to fix that?  Help would be much welcomed :)

Not a way to fix it but to circumvent it.  Do you need sim support (it's
a simulator hosted inside GDB)?  If not, you can configure with
--disable-sim, it will skip configuring/building the sim directory.

Simon