x86/crypto/sha_ni: Standardize stack alignment prologue

Use a more standard prologue for saving the stack pointer before
realigning the stack.

This enables ORC unwinding by allowing objtool to understand the stack
realignment.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Link: https://lore.kernel.org/r/5033e1a79867dff1b18e1b4d0783c38897d3f223.1614182415.git.jpoimboe@redhat.com

arch/x86/crypto/sha1_ni_asm.S

@@ -59,8 +59,6 @@
 #define DATA_PTR	%rsi	/* 2nd arg */
 #define NUM_BLKS	%rdx	/* 3rd arg */
 
-#define RSPSAVE		%rax
-
 /* gcc conversion */
 #define FRAME_SIZE	32	/* space for 2x16 bytes */
 
@@ -96,7 +94,8 @@
 .text
 .align 32
 SYM_FUNC_START(sha1_ni_transform)
-	mov		%rsp, RSPSAVE
+	push		%rbp
+	mov		%rsp, %rbp
 	sub		$FRAME_SIZE, %rsp
 	and		$~0xF, %rsp
 
@@ -288,7 +287,8 @@ SYM_FUNC_START(sha1_ni_transform)
 	pextrd		$3, E0, 1*16(DIGEST_PTR)
 
 .Ldone_hash:
-	mov		RSPSAVE, %rsp
+	mov		%rbp, %rsp
+	pop		%rbp
 
 	ret
 SYM_FUNC_END(sha1_ni_transform)