GCC8: Is --with-cpu= allowed for ARM targets?

[Alexey Neyman <stilor at att dot net>]

Hi,

I am seeing a failure to build in crosstool-NG configurations where GCC8 
is configured with --with-cpu=... option:

[ALL  ]    libtool: compile: 
/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/build/build-cc-gcc-final/./gcc/xgcc 
-B/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/build/build-cc-gcc-final/./gcc/ 
-B/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/bin/ 
-B/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/lib/ 
-isystem 
/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/include 
-isystem 
/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/sys-include 
-DHAVE_CONFIG_H 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/libatomic/config/arm 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/libatomic/config/linux/arm 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/libatomic/config/posix 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/libatomic 
-I. -Wall -Werror -pthread -mlittle-endian -mcpu=cortex-a15 
-mfpu=neon-vfpv4 -mhard-float -g -Os -MT load_1_1_.lo -MD -MP -MF 
.deps/load_1_1_.lo.Ppo -DN=1 -DIFUNC_ALT=1 -march=armv7-a+fp -c 
/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/libatomic/config/linux/arm/load_n.c 
-fPIC -DPIC -o .libs/load_1_1_.o
[ERROR]    cc1: error: switch -mcpu=cortex-a15 conflicts with 
-march=armv7-a switch [-Werror]

GCC is configured with:

CC_FOR_BUILD='x86_64-build_pc-linux-gnu-gcc' CFLAGS='-O2 -g -pipe 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools/include 
' CFLAGS_FOR_BUILD='-O2 -g -pipe 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools/include 
' CXXFLAGS='-O2 -g -pipe 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools/include 
' CXXFLAGS_FOR_BUILD='-O2 -g -pipe 
-I/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools/include 
' 
LDFLAGS='-L/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools/lib 
-lstdc++ -lm' CFLAGS_FOR_TARGET='   -mlittle-endian -mcpu=cortex-a15  
-mfpu=neon-vfpv4 -mhard-float ' CXXFLAGS_FOR_TARGET='   
-mlittle-endian   -mcpu=cortex-a15 -mfpu=neon-vfpv4 -mhard-float ' 
LDFLAGS_FOR_TARGET='   -Wl,-EL ' '/bin/bash' 
'/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/src/gcc/configure' 
'--build=x86_64-build_pc-linux-gnu' '--host=x86_64-build_pc-linux-gnu' 
'--target=arm-cortex_a15-linux-gnueabihf' 
'--prefix=/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf' 
'--with-sysroot=/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/sysroot' 
'--enable-languages=c,c++' '--with-cpu=cortex-a15' 
'--with-fpu=neon-vfpv4' '--with-float=hard' 
'--with-pkgversion=crosstool-NG 1.23.0-392-gd274ab06-dirty' 
'--enable-__cxa_atexit' '--disable-libmudflap' '--disable-libgomp' 
'--disable-libssp' '--disable-libquadmath' 
'--disable-libquadmath-support' '--disable-libsanitizer' 
'--disable-libmpx' 
'--with-gmp=/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools' 
'--with-mpfr=/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools' 
'--with-mpc=/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools' 
'--with-isl=/home/avn/work/ctng/crosstool-ng/.build/arm-cortex_a15-linux-gnueabihf/buildtools' 
'--enable-lto' '--with-host-libstdcxx=-static-libgcc 
-Wl,-Bstatic,-lstdc++,-Bdynamic -lm' '--enable-threads=posix' 
'--enable-target-optspace' '--enable-plugin' '--enable-gold' 
'--disable-nls' '--disable-multilib' 
'--with-local-prefix=/home/avn/x-tools/arm-cortex_a15-linux-gnueabihf/arm-cortex_a15-linux-gnueabihf/sysroot' 
'--enable-long-long'

The problem, as far as I understand, is that libatomic unconditionally 
adds -march=armv7-a for arm-*-linux configurations; here is a fragment 
of its Makefile.am:

## On a target-specific basis, include alternates to be selected by IFUNC.
if HAVE_IFUNC
...
if ARCH_ARM_LINUX
IFUNC_OPTIONS        = -march=armv7-a+fp -DHAVE_KERNEL64
libatomic_la_LIBADD += $(foreach s,$(SIZES),$(addsuffix 
_$(s)_1_.lo,$(SIZEOBJS)))
libatomic_la_LIBADD += $(addsuffix _8_2_.lo,$(SIZEOBJS))
endif

The -mcpu=cortex-a15 comes from the CPU selected during configure.

Is --with-cpu still allowed for ARM/Linux targets with GCC8? If it is, 
what should be the fix for this - only add -march=... if CPU is not 
selected?

Regards,
Alexey.