Change in coreboot[master]: x86/smm: Preserve local variables whan aligning stack

[Marshall Dawson (Code Review)]

Marshall Dawson has uploaded this change for review. ( https://review.coreboot.org/22949

Change subject: x86/smm: Preserve local variables whan aligning stack
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x86/smm: Preserve local variables whan aligning stack

Align the stack earlier and account for all local variables.

Ensure %edi, containing the fxsave/fxrstor location, can be properly
retrieved from the stack prior to the rsm instruction.

This corrects an observed bug where the stack had a 16-byte alignment,
%edi was pushed, then the stack was realigned for the call to
c_handler.  After returning, garbage was popped into %edi and the
system rebooted as a result of the fxrstor instruction.

BUG=b:70027919
TEST=Boot Kahlee to the OS

Change-Id: Ic06cdf8bd95d9aaa9634ecf3546a5033150fe82b
Signed-off-by: Marshall Dawson 
---
M src/cpu/x86/smm/smm_stub.S
1 file changed, 8 insertions(+), 3 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/49/22949/1

diff --git a/src/cpu/x86/smm/smm_stub.S b/src/cpu/x86/smm/smm_stub.S
index 32435a0..f5a30d4 100644
--- a/src/cpu/x86/smm/smm_stub.S
+++ b/src/cpu/x86/smm/smm_stub.S
@@ -145,6 +145,14 @@
    add	%eax, %edi

2:
+	/* Align the stack before saving any local information.  This takes
+	 * into account that the stack must be in proper alignment at the time
+	 * the call to c_handler is made.  That is, c_handler's stack must be
+	 * aligned so that %esp+4 (or %rsp+8) is a multiple of 16.
+	 */
+	andl	$0xfffffff0, %esp
+	sub	$12, %esp
+
    /* Save location of fxsave area. */
    push	%edi
    mov	%esp, %ebp
@@ -160,9 +168,6 @@
    fxsave	(%edi)

1:
-	/* Align stack to 16 bytes. Another 16 bytes are pushed below. */
-	andl	$0xfffffff0, %esp
-
    /* Call into the c-based SMM relocation function with the platform
     * parameters. Equivalent to:
     *   struct arg = { c_handler_params, cpu_num, smm_runtime {;