arm64: Change .weak to SYM_FUNC_START_WEAK_PI for arch/arm64/lib/mem*.S

commit ec9d78070de986ecf581ea204fd322af4d2477ec upstream.

Commit 39d114ddc682 ("arm64: add KASAN support") added .weak directives to
arch/arm64/lib/mem*.S instead of changing the existing SYM_FUNC_START_PI
macros. This can lead to the assembly snippet `.weak memcpy ... .globl
memcpy` which will produce a STB_WEAK memcpy with GNU as but STB_GLOBAL
memcpy with LLVM's integrated assembler before LLVM 12. LLVM 12 (since
https://reviews.llvm.org/D90108) will error on such an overridden symbol
binding.

Use the appropriate SYM_FUNC_START_WEAK_PI instead.

Fixes: 39d114ddc682 ("arm64: add KASAN support")
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20201029181951.1866093-1-maskray@google.com
Signed-off-by: Will Deacon <will@kernel.org>
[nd: backport to adjust for missing:
  commit 3ac0f4526dfb ("arm64: lib: Use modern annotations for assembly functions")
  commit 35e61c77ef38 ("arm64: asm: Add new-style position independent function annotations")]
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Change-Id: I63c34385861c5a84cdf332a912f5ee53dedac3bd

arch/arm64/lib/memcpy.S

@@ -68,9 +68,8 @@
 	stp \ptr, \regB, [\regC], \val
 	.endm
 
-	.weak memcpy
 ENTRY(__memcpy)
-ENTRY(memcpy)
+WEAK(memcpy)
 #include "copy_template.S"
 	ret
 ENDPIPROC(memcpy)

arch/arm64/lib/memmove.S

@@ -57,9 +57,8 @@ C_h	.req	x12
 D_l	.req	x13
 D_h	.req	x14
 
-	.weak memmove
 ENTRY(__memmove)
-ENTRY(memmove)
+WEAK(memmove)
 	cmp	dstin, src
 	b.lo	__memcpy
 	add	tmp1, src, count

arch/arm64/lib/memset.S

@@ -54,9 +54,8 @@ dst		.req	x8
 tmp3w		.req	w9
 tmp3		.req	x9
 
-	.weak memset
 ENTRY(__memset)
-ENTRY(memset)
+WEAK(memset)
 	mov	dst, dstin	/* Preserve return value.  */
 	and	A_lw, val, #255
 	orr	A_lw, A_lw, A_lw, lsl #8