https://github.com/libffi/libffi/issues/668
--- a/src/powerpc/linux64.S
+++ b/src/powerpc/linux64.S
@@ -29,6 +29,8 @@
 #include <fficonfig.h>
 #include <ffi.h>
 
+	.machine altivec
+
 #ifdef POWERPC64
 	.hidden	ffi_call_LINUX64
 	.globl	ffi_call_LINUX64
--- a/src/powerpc/linux64_closure.S
+++ b/src/powerpc/linux64_closure.S
@@ -30,6 +30,8 @@
 
 	.file	"linux64_closure.S"
 
+	.machine altivec
+
 #ifdef POWERPC64
 	FFI_HIDDEN (ffi_closure_LINUX64)
 	.globl  ffi_closure_LINUX64