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x86: Use a simple jump into long mode

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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 <sjg@chromium.org>
This commit is contained in:
Simon Glass
2025-03-15 14:25:39 +00:00
committed by Tom Rini
parent f5b1c643b4
commit ffd92a25be
1 changed files with 7 additions and 10 deletions
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17
arch/x86/cpu/i386/call64.S
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@@ -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: