[Buildroot] Thread support in Cortex m4 toolchains, was: Re: Update of Buildroot toolchains on autobuild.b.o

[Bernd Kuhls]

Am Mon, 13 Jun 2016 23:48:25 +0200 schrieb Waldemar Brodkorb:

> Thread model: single
> gcc version 4.4.1 (Sourcery G++ Lite 2010q1-189) 
> 
> I would say it is normal for any *-uclinux-* toolchain using
> linuxthreads instead of NPTL.

Hi Waldemar,

how to distinguish a toolchain using linuxthreads from a
toolchain lacking thread support?

The toolchain from
http://autobuild.buildroot.net/toolchains/configs/br-arm-full-
nothread.config
shows a similar output to the m4 toolchain

$ output/host/opt/ext-toolchain/bin/arm-buildroot-linux-uclibcgnueabihf-
gcc -v
Using built-in specs.
COLLECT_GCC=/home/bernd/buildroot/br2/output/host/opt/ext-toolchain/bin/
arm-buildroot-linux-uclibcgnueabihf-gcc.br_real
COLLECT_LTO_WRAPPER=/home/bernd/buildroot/br2/output/host/opt/ext-
toolchain/bin/../libexec/gcc/arm-buildroot-linux-uclibcgnueabihf/4.9.3/
lto-wrapper
Target: arm-buildroot-linux-uclibcgnueabihf
Configured with: ./configure --prefix=/opt/br-arm11-full-
nothread-2016.05-2-g5dabb45/usr --sysconfdir=/opt/br-arm11-full-
nothread-2016.05-2-g5dabb45/etc --enable-static --target=arm-buildroot-
linux-uclibcgnueabihf --with-sysroot=/opt/br-arm11-full-
nothread-2016.05-2-g5dabb45/usr/arm-buildroot-linux-uclibcgnueabihf/
sysroot --disable-__cxa_atexit --with-gnu-ld --disable-libssp --disable-
multilib --with-gmp=/opt/br-arm11-full-nothread-2016.05-2-g5dabb45/usr --
with-mpfr=/opt/br-arm11-full-nothread-2016.05-2-g5dabb45/usr --with-
pkgversion='Buildroot 2016.05-00002-g5dabb45' --with-bugurl=http://
bugs.buildroot.net/ --disable-libsanitizer --disable-tls --disable-
libmudflap --disable-threads --disable-libitm --disable-libatomic --with-
mpc=/opt/br-arm11-full-nothread-2016.05-2-g5dabb45/usr --without-isl --
without-cloog --disable-decimal-float --with-abi=aapcs-linux --with-
cpu=arm1176jzf-s --with-fpu=vfp --with-float=hard --with-mode=arm --
enable-languages=c,c++ --with-build-time-tools=/opt/br-arm11-full-
nothread-2016.05-2-g5dabb45/usr/arm-buildroot-linux-uclibcgnueabihf/bin --
enable-shared --disable-libgomp
Thread model: single
gcc version 4.9.3 (Buildroot 2016.05-00002-g5dabb45) 

This toolchain, as expected, lacks the definition of 
_GLIBCXX_HAS_GTHREADS in
output/host/opt/ext-toolchain/arm-buildroot-linux-uclibcgnueabihf/include/
c++/4.9.3/arm-buildroot-linux-uclibcgnueabihf/bits/c++config.h

The same is valid for the Cortex m4 toolchain however despite the fact 
that it claims to have thread support in Kconfig. This leads to build 
errors in the boost package:
http://autobuild.buildroot.net/
results/422/4220e275dcc90e64545ad2d5ed3e0b51044f6426/

./boost/config/requires_threads.hpp:29:4: error: #error "Threading 
support unavaliable: it has been explicitly disabled with 
BOOST_DISABLE_THREADS"
 #  error "Threading support unavaliable: it has been explicitly disabled 
with BOOST_DISABLE_THREADS"

Boost checks for _GLIBCXX_HAS_GTHREADS to determine thread support:
https://github.com/boostorg/config/blob/develop/include/boost/config/
stdlib/libstdcpp3.hpp#L37

Afaics we have two choices: Fix the thread support in gcc or remove the 
setting that the m4 toolchain supports threads.

Regards, Bernd