The bug report http://golang.org/issue/7074 shows that math.Log2(1) produces the wrong result on Aarch64, because the Go math package is compiled to use a fused multiply-add instruction. This patch to the libgo configure script will use -ffp-contract=off when compiling the math package on processors other than x86. Bootstrapped and ran Go testsuite on x86_64-unknown-linux-gnu, not that that tests much. Committed to mainline.
Ian
diff -r 76dbb6f77e3d libgo/configure.ac --- a/libgo/configure.ac Tue Mar 11 12:53:06 2014 -0700 +++ b/libgo/configure.ac Tue Mar 11 21:26:35 2014 -0700 @@ -620,6 +620,8 @@ MATH_FLAG= if test "$libgo_cv_c_fancymath" = yes; then MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations" +else + MATH_FLAG="-ffp-contract=off" fi AC_SUBST(MATH_FLAG)
