diff options
Diffstat (limited to 'src/cpu/x86/64bit/exit32.inc')
| -rw-r--r-- | src/cpu/x86/64bit/exit32.inc | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/src/cpu/x86/64bit/exit32.inc b/src/cpu/x86/64bit/exit32.inc new file mode 100644 index 0000000000..48837d96a9 --- /dev/null +++ b/src/cpu/x86/64bit/exit32.inc @@ -0,0 +1,84 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +/* + * For droping from long mode to protected mode. + * + * For reference see "AMD64 ArchitectureProgrammer's Manual Volume 2", + * Document 24593-Rev. 3.31-July 2019 Chapter 5.3 + * + * Clobbers: rax, rbx, rcx, rdx + */ +.code64 + +#include <cpu/x86/msr.h> +#include <cpu/x86/cr.h> +#include <arch/rom_segs.h> + +drop_longmode: + /* Ensure cache is clean. */ + wbinvd + + /* Set 32-bit code segment and ss */ + mov $ROM_CODE_SEG, %rcx + /* SetCodeSelector32 will drop us to protected mode on return */ + call SetCodeSelector32 + + /* Skip SetCodeSelector32 */ +.code32 + jmp __longmode_compatibility + +.align 8 +.code64 +SetCodeSelector32: + # pop the return address from stack + pop %rbx + + # save rsp because we need to push it after ss + mov %rsp, %rdx + + # use iret to jump to a 32-bit offset in a new code segment + # iret will pop cs:rip, flags, then ss:rsp + mov %ss, %ax # need to push ss, but push ss instuction + push %rax # not valid in x64 mode, so use ax + push %rdx # the rsp to load + pushfq # push rflags + push %rcx # cx is code segment selector from caller + push %rbx # push the IP for the next instruction + + # the iretq will behave like ret, with the new cs/ss value loaded + iretq + +.align 4 +.code32 +__longmode_compatibility: + /* Running in 32-bit compatibility mode */ + + /* Use flat data segment */ + movl $ROM_DATA_SEG, %eax + movl %eax, %ds + movl %eax, %es + movl %eax, %ss + movl %eax, %fs + movl %eax, %gs + + /* Disable paging. */ + movl %cr0, %eax + andl $(~CR0_PG), %eax + movl %eax, %cr0 + + /* Disable long mode. */ + movl $(IA32_EFER), %ecx + rdmsr + andl $(~EFER_LME), %eax + wrmsr + + /* Disable PAE. */ + movl %cr4, %eax + andl $(~CR4_PAE), %eax + movl %eax, %cr4 + + /* Clear page table register */ + xor %eax, %eax + movl %eax, %cr3 + +__longmode_exit: |