My flags are set by me in this way to found problems like this. From build.log: x86_64-pc-linux-gnu-g++ -Wall -ansi -DHAVE_CONFIG_H -D_FILE_OFFSET_BITS=64 -DUSEGC -DTRANSJUMP -DHAVE_SYS_TYPES_H -march=native -O2 -g0 --no-var-tracking -I . -I/usr/include/gc -I/usr/include/gc -o tr.o -c tr.cc amd64box binutils # emerge --info | grep CXX CXXFLAGS="-march=native -O2" amd64box binutils # emerge --info | grep CFLAGS CFLAGS="-march=native -O2 -g0" So it uses CFLAGS
Thanks, fixed.