With the 64-bit descriptor we can use a jump instruction, rather than
pushing things on the stack.
Since the processor is in 64-bit mode by this point, pop a 64-bit value
from the stack, containing the target address.
This simplifies the code slightly, in particular its use of the stack.
Signed-off-by: Simon Glass <s...@chromium.org>
---
(no changes since v1)
arch/x86/cpu/i386/call64.S | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/arch/x86/cpu/i386/call64.S b/arch/x86/cpu/i386/call64.S
index 3137ec17d31..c6308b92e25 100644
--- a/arch/x86/cpu/i386/call64.S
+++ b/arch/x86/cpu/i386/call64.S
@@ -22,6 +22,7 @@ cpu_call64:
* ecx - target
*/
cli
+ pushl $0 /* top 64-bits of target */
push %ecx /* arg2 = target */
push %edx /* arg1 = setup_base */
mov %eax, %ebx
@@ -32,7 +33,8 @@ cpu_call64:
movl %eax, %cr0
/* Enable PAE mode */
- movl $(X86_CR4_PAE), %eax
+ movl %cr4, %eax
+ orl $X86_CR4_PAE, %eax
movl %eax, %cr4
/* Enable the boot page tables */
@@ -57,23 +59,18 @@ cpu_call64:
*/
pop %esi /* setup_base */
- pushl $(X86_GDT_ENTRY_64BIT_CS * X86_GDT_ENTRY_SIZE)
- leal lret_target, %eax
- pushl %eax
-
/* Enter paged protected Mode, activating Long Mode */
movl %cr0, %eax
orl $X86_CR0_PG, %eax
movl %eax, %cr0
/* Jump from 32bit compatibility mode into 64bit mode. */
- lret
+ ljmp $(X86_GDT_ENTRY_64BIT_CS * X86_GDT_ENTRY_SIZE), $lret_target
-code64:
+.code64
lret_target:
- pop %eax /* target */
- mov %eax, %eax /* Clear bits 63:32 */
- jmp *%eax /* Jump to the 64-bit target */
+ pop %rax /* target */
+ jmp *%rax /* Jump to the 64-bit target */
.globl call64_stub_size
call64_stub_size:
--
2.43.0
