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Kernel: Avoid unnecessary jump in the boot code

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The 32-bit boot code jumps to 0xc0000000 + entry address once page
tables are set up. This is unnecessary for 64-bit mode because we'll
do another far jump just moments later.
This commit is contained in:
Gunnar Beutner 2021-07-14 12:51:07 +02:00 • committed by Andreas Kling
parent eb1935b62e
commit 9b431cbe42
1 changed files with 20 additions and 17 deletions
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37
Kernel/Arch/x86/common/Boot/boot.S
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@ -522,23 +522,6 @@ pae_supported:
mov $stack_top, %esp
and $-16, %esp
/* jmp to an address above the 3GB mark */
movl $1f,%eax
jmp *%eax
1:
movl %cr3, %eax
movl %eax, %cr3
/* unmap the 0-1MB range, which isn't used after jmp-ing up here */
movl $256, %ecx
movl $(boot_pd0_pt0 - KERNEL_BASE), %edi
xorl %eax, %eax
1:
movl %eax, 0(%edi)
addl $8, %edi
loop 1b
/* jump into C++ land */
addl $KERNEL_BASE, %ebx
movl %ebx, multiboot_info_ptr
@ -556,8 +539,28 @@ pae_supported:
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
mov %cr3, %rax
mov %rax, %cr3
#else
/* jmp to an address above the 3GB mark */
movl $1f,%eax
jmp *%eax
1:
movl %cr3, %eax
movl %eax, %cr3
#endif
/* unmap the 0-1MB range, which isn't used after jmp-ing up here */
movl $256, %ecx
movl $(boot_pd0_pt0 - KERNEL_BASE), %edi
xorl %eax, %eax
1:
movl %eax, 0(%edi)
addl $8, %edi
loop 1b
call init
#if ARCH(X86_64)
add $4, %rsp