https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72815
--- Comment #4 from vicencb at gmail dot com --- I can confirm that with the provided list of steps it is still reproducible. To obtain the buildroot version use this: #### cd /tmp git clone git://git.buildroot.net/buildroot cd buildroot git checkout eb1a30a3d92c8ddbcc295cb48226604d6d881e25 #### And then following the steps, this is the error message reported (including the command line invocation): #### Making all in mpxrt /bin/sh ../libtool --tag=CC --mode=compile /tmp/buildroot/output/build/host-gcc-final-6.1.0/build/./gcc/xgcc -B/tmp/buildroot/output/build/host-gcc-final-6.1.0/build/./gcc/ -B/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/bin/ -B/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/lib/ -isystem /tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/include -isystem /tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/sys-include -DHAVE_CONFIG_H -I. -I../../../../libmpx/mpxrt -I.. -I../../../../libmpx/.. -fPIC -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -c -o libmpx_la-mpxrt.lo `test -f 'mpxrt.c' || echo '../../../../libmpx/mpxrt/'`mpxrt.c libtool: compile: /tmp/buildroot/output/build/host-gcc-final-6.1.0/build/./gcc/xgcc -B/tmp/buildroot/output/build/host-gcc-final-6.1.0/build/./gcc/ -B/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/bin/ -B/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/lib/ -isystem /tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/include -isystem /tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/sys-include -DHAVE_CONFIG_H -I. -I../../../../libmpx/mpxrt -I.. -I../../../../libmpx/.. -fPIC -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -c ../../../../libmpx/mpxrt/mpxrt.c -fPIC -DPIC -o .libs/libmpx_la-mpxrt.o In file included from ../../../../libmpx/mpxrt/mpxrt.c:54:0: ../../../../libmpx/mpxrt/mpxrt.c: In function 'read_mpx_status_sig': ../../../../libmpx/mpxrt/mpxrt.h:52:42: error: invalid application of 'sizeof' to incomplete type 'struct _libc_fpstate' #define XSAVE_OFFSET_IN_FPMEM sizeof (struct _libc_fpstate) ^ ../../../../libmpx/mpxrt/mpxrt.c:132:58: note: in expansion of macro 'XSAVE_OFFSET_IN_FPMEM' uint8_t *regs = (uint8_t *)uctxt->uc_mcontext.fpregs + XSAVE_OFFSET_IN_FPMEM; ^~~~~~~~~~~~~~~~~~~~~ #### And the gcc configuration from /tmp/buildroot/output/build/host-gcc-final-6.1.0/build/gcc/config.log: #### $ /tmp/buildroot/output/build/host-gcc-final-6.1.0/gcc/configure --srcdir=../../gcc --cache-file=./config.cache --prefix=/tmp/i686-buildroot-linux-musl/usr/usr --sysconfdir=/tmp/i686-buildroot-linux-musl/usr/etc --enable-static --with-sysroot=/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/sysroot --disable-__cxa_atexit --with-gnu-ld --disable-libssp --disable-multilib --with-gmp=/tmp/i686-buildroot-linux-musl/usr/usr --with-mpfr=/tmp/i686-buildroot-linux-musl/usr/usr --with-pkgversion=Buildroot 2016.08-git-01592-geb1a30a3d --with-bugurl=http://bugs.buildroot.net/ --enable-libquadmath --disable-libsanitizer --disable-tls --enable-plugins --enable-lto --disable-libmudflap --enable-threads --with-mpc=/tmp/i686-buildroot-linux-musl/usr/usr --with-isl=/tmp/i686-buildroot-linux-musl/usr/usr --disable-decimal-float --with-arch=i686 --with-build-time-tools=/tmp/i686-buildroot-linux-musl/usr/usr/i686-buildroot-linux-musl/bin --enable-shared --disable-libgomp --enable-languages=c,c++,lto --program-transform-name=s&^&i686-buildroot-linux-musl-& --disable-option-checking --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --target=i686-buildroot-linux-musl #### Please, note that this is a crosscompiler. I hope this helps fixing the bug. Regards.