[S] Change in coreboot[main]: arch/x86/c_start.S: Add proper x86_64 code

[Lean Sheng Tan (Code Review)]

Lean Sheng Tan has submitted this change. ( https://review.coreboot.org/c/coreboot/+/59874?usp=email )

Change subject: arch/x86/c_start.S: Add proper x86_64 code
......................................................................

arch/x86/c_start.S: Add proper x86_64 code

Don't truncate upper bits in assembly code and thus allow loading
of ramstage above 4GiB.

Tested on qemu with cbmem_top set to TOUUD.

Change-Id: Ifc9b45f69d0b7534b2faacaad0d099cef2667478
Signed-off-by: Patrick Rudolph 
Co-authored-by: Benjamin Doron 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59874
Tested-by: build bot (Jenkins) 
---
M src/arch/x86/c_start.S
1 file changed, 24 insertions(+), 0 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  Patrick Rudolph: Looks good to me, approved

diff --git a/src/arch/x86/c_start.S b/src/arch/x86/c_start.S
index 02ddf75..6bea8db 100644
--- a/src/arch/x86/c_start.S
+++ b/src/arch/x86/c_start.S
@@ -59,6 +59,24 @@
    leal	_stack, %edi
 #endif

+#if ENV_X86_64
+	/** poison the stack. Code should not count on the
+	 * stack being full of zeros. This stack poisoning
+	 * recently uncovered a bug in the broadcast SIPI
+	 * code.
+	 */
+	movabs	$_estack, %rcx
+	sub	%rdi, %rcx
+	shr	$3, %rcx   /* it is 64 bit aligned, right? */
+	movq	$0xDEADBEEFDEADBEEF, %rax
+	rep
+	stosq
+
+	/* Set new stack with enforced alignment. */
+	movabs	$_estack, %rsp
+	movq	$(0xfffffffffffffff0), %rax
+	and	%rax, %rsp
+#else
    /** poison the stack. Code should not count on the
     * stack being full of zeros. This stack poisoning
     * recently uncovered a bug in the broadcast SIPI
@@ -74,6 +92,7 @@
    /* Set new stack with enforced alignment. */
    movl	$_estack, %esp
    andl	$(0xfffffff0), %esp
+#endif

/*
     *	Now we are finished. Memory is up, data is copied and
@@ -82,7 +101,12 @@
     */
    post_code(POSTCODE_PRE_HARDWAREMAIN)	/* post 6e */

+#if ENV_X86_64
+	movq	$0xFFFFFFFFFFFFFFF0, %rax
+	and	%rax, %rsp
+#else
    andl	$0xFFFFFFF0, %esp
+#endif

#if CONFIG(ASAN_IN_RAMSTAGE)
    call asan_init