quoted

+/*
+ * Minimum alignment requirement for the source and destination addresses
+ * for function copying.
+ */
+#define FNCPY_ALIGN 8

quoted

From now this is not arm-only, and it's possible that some architectures

might want to redefine it in their arch/xxx/include/asm/fncpy.h files.
So it will be easier for them if you'll wrap FNCPY_ALIGN here with #ifdef
guards.

By the way, compiler already has an information on the proper alignment.
Maybe it's better to use it as the default value here instead of the
hardcoded value?

#ifndef FNCPY_ALIGN
#define FNCPY_ALIGN ({void foo(); __alignof__(&foo);})
#endif

Ah sorry, at first it should be like this:
#define FNCPY_ALIGN ({void foo(); __alignof__(foo);})

And at second, the correct version returns 1 always.

Even if I pass falign-functions=4096 to gcc, and I see that functions
are aligned accordingly in elf file, the macro returns 1 anyway. So if 
it doesn't work, the hardcoded '8' is the only option.

Yury