diff --git a/misc/cgo/testshared/test.bash b/misc/cgo/testshared/test.bash
index 21004adaf8..0b0d0411f7 100755
--- a/misc/cgo/testshared/test.bash
+++ b/misc/cgo/testshared/test.bash
@@ -78,6 +78,7 @@ ensure_ldd $rootdir/libdep.so $std_install_dir/$soname
 
 # And exe that links against both
 go install -installsuffix="$mysuffix" -linkshared exe
+./bin/exe || die "./bin/exe failed with code $?"
 ensure_ldd ./bin/exe $rootdir/libdep.so
 ensure_ldd ./bin/exe $std_install_dir/$soname
 
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 36353d108f..0f9aeb8f37 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -1693,8 +1693,10 @@ TEXT runtime·prefetchnta(SB),NOSPLIT,$0-8
 	RET
 
 // This is called from .init_array and follows the platform, not Go, ABI.
-TEXT runtime·addmoduledata(SB),NOSPLIT,$0-8
+TEXT runtime·addmoduledata(SB),NOSPLIT,$0-0
+	PUSHQ	R15 // The access to global variables below implicitly uses R15, which is callee-save
 	MOVQ	runtime·lastmoduledatap(SB), AX
 	MOVQ	DI, moduledata_next(AX)
 	MOVQ	DI, runtime·lastmoduledatap(SB)
+	POPQ	R15
 	RET