Bug when cross-compiling for ppc

Bug when cross-compiling for ppc

[Vincent Fortier]

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 :)

Re: Bug when cross-compiling for ppc

[Simon Marchi]

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

Re: Bug when cross-compiling for ppc

[Simon Marchi]

On 9/13/23 22:25, Simon Marchi via Gdb wrote:
> 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.

Also, what does you full configure line looks like?

Simon

Re: Bug when cross-compiling for ppc

[Andreas Schwab]

On Sep 12 2023, Vincent Fortier via Gdb wrote:

> Now the question is, how to fix that?  Help would be much welcomed :)

You need to set CFLAGS_FOR_BUILD (to something non-empty), so it does
not default to $CFLAGS (which is questionable in the first place).

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."

Re: Bug when cross-compiling for ppc

[Vincent Fortier]

Le jeu. 14 sept. 2023, à 02 h 24, Andreas Schwab <schwab@suse.de> a écrit :
>
> On Sep 12 2023, Vincent Fortier via Gdb wrote:
>
> > Now the question is, how to fix that?  Help would be much welcomed :)
>
> You need to set CFLAGS_FOR_BUILD (to something non-empty), so it does
> not default to $CFLAGS (which is questionable in the first place).
>
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."

For a start, I ended-up disabling sim entirely for PPC and now it's
building just fine.  I had found a ticket from openwrt having a
somewhat similar issue that was disabling it as well.  So I used that
option too.

I've tried that by setting CFLAGS_FOR_BUILD='-O2' just for the sake of
it not being empty but I'm still getting errors:
compilation terminated.
make[7]: *** [Makefile:660: table.o] Error 1
In file included from ./gen-icache.c:22:
./misc.h:23:10: fatal error: build-config.h: No such file or directory
   23 | #include "build-config.h"
      |          ^~~~~~~~~~~~~~~~

Further looking into the logs there's this hidden in a temporary
directory (once rm of it is commented out)
configure:2482: checking whether the C compiler works
configure:2504: gcc -O2
-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

The exec string from sim/ppc is
$ .././configure --enable-languages=all
--target=powerpc-e500v2-linux-gnuspe --host=i686-pc-linux
--build=i686-pc-linux

But as you can see I believe it refers to the "build" C compiler
instead of the"target" compiler OR uses the "target" flags instead of
the "build" flags (wonder why it would?).

Anyhow, disabling sim/ppc fixed things for now.

Migrating gdb to cmake using toolchain files or meson would
potentially remove these issues and simplify cross-compiling while
reducing build time.  But that's unrelated...