x86/crypto/sha256-avx2: 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/8048e7444c49a8137f05265262b83dc50f8fb7f3.1614182415.git.jpoimboe@redhat.com

arch/x86/crypto/sha256-avx2-asm.S

@@ -117,15 +117,13 @@ _XMM_SAVE_SIZE	= 0
 _INP_END_SIZE	= 8
 _INP_SIZE	= 8
 _CTX_SIZE	= 8
-_RSP_SIZE	= 8
 
 _XFER		= 0
 _XMM_SAVE	= _XFER     + _XFER_SIZE
 _INP_END	= _XMM_SAVE + _XMM_SAVE_SIZE
 _INP		= _INP_END  + _INP_END_SIZE
 _CTX		= _INP      + _INP_SIZE
-_RSP		= _CTX      + _CTX_SIZE
-STACK_SIZE	= _RSP      + _RSP_SIZE
+STACK_SIZE	= _CTX      + _CTX_SIZE
 
 # rotate_Xs
 # Rotate values of symbols X0...X3
@@ -533,11 +531,11 @@ SYM_FUNC_START(sha256_transform_rorx)
 	pushq	%r14
 	pushq	%r15
 
-	mov	%rsp, %rax
+	push	%rbp
+	mov	%rsp, %rbp
+
 	subq	$STACK_SIZE, %rsp
 	and	$-32, %rsp	# align rsp to 32 byte boundary
-	mov	%rax, _RSP(%rsp)
-
 
 	shl	$6, NUM_BLKS	# convert to bytes
 	jz	done_hash
@@ -704,7 +702,8 @@ only_one_block:
 
 done_hash:
 
-	mov	_RSP(%rsp), %rsp
+	mov	%rbp, %rsp
+	pop	%rbp
 
 	popq	%r15
 	popq	%r14