diff options
| author | Simon Glass <sjg@chromium.org> | 2015-08-04 12:33:55 -0600 |
|---|---|---|
| committer | Simon Glass <sjg@chromium.org> | 2015-08-05 08:44:07 -0600 |
| commit | 6f92ed8f1abfe94ee1c96c83c21f4092bb04ff63 (patch) | |
| tree | f487163b3e28006dbe9023ae8c6c3abfbd211461 /arch/x86/cpu | |
| parent | 7dfe8bdeef7f8a7223fb39e04faaa5c7489feb3f (diff) | |
x86: Add a way to call 32-bit code from 64-bit mode
The procedure to drop from 64-bit mode to 32-bit is a bit messy. Add a
function to take care of it. It requires identity-mapped pages and that
the calling code is running below 4GB.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Diffstat (limited to 'arch/x86/cpu')
| -rw-r--r-- | arch/x86/cpu/Makefile | 6 | ||||
| -rw-r--r-- | arch/x86/cpu/call32.S | 64 |
2 files changed, 70 insertions, 0 deletions
diff --git a/arch/x86/cpu/Makefile b/arch/x86/cpu/Makefile index 5e058c0c09..e7979254db 100644 --- a/arch/x86/cpu/Makefile +++ b/arch/x86/cpu/Makefile @@ -12,6 +12,12 @@ extra-y = start.o obj-$(CONFIG_X86_RESET_VECTOR) += resetvec.o start16.o obj-y += interrupts.o cpu.o cpu_x86.o call64.o +AFLAGS_REMOVE_call32.o := -mregparm=3 \ + $(if $(CONFIG_EFI_STUB_64BIT),-march=i386 -m32) +AFLAGS_call32.o := -fpic -fshort-wchar + +extra-y += call32.o + obj-$(CONFIG_INTEL_BAYTRAIL) += baytrail/ obj-$(CONFIG_SYS_COREBOOT) += coreboot/ obj-$(CONFIG_EFI_APP) += efi/ diff --git a/arch/x86/cpu/call32.S b/arch/x86/cpu/call32.S new file mode 100644 index 0000000000..c517e4a89f --- /dev/null +++ b/arch/x86/cpu/call32.S @@ -0,0 +1,64 @@ +/* + * (C) Copyright 2015 Google, Inc + * Written by Simon Glass <sjg@chromium.org> + * + * SPDX-License-Identifier: GPL-2.0+ + */ + +#include <asm/global_data.h> +#include <asm/msr-index.h> +#include <asm/processor-flags.h> + + /* + * rdi - 32-bit code segment selector + * rsi - target address + * rdx - table address (0 if none) + */ +.code64 +.globl cpu_call32 +cpu_call32: + cli + + /* Save table pointer */ + mov %edx, %ebx + + /* + * Debugging option, this outputs characters to the console UART + * mov $0x3f8,%edx + * mov $'a',%al + * out %al,(%dx) + */ + + pushf + push %rdi /* 32-bit code segment */ + lea compat(%rip), %rax + push %rax + .byte 0x48 /* REX prefix to force 64-bit far return */ + retf +.code32 +compat: + /* + * We are now in compatibility mode with a default operand size of + * 32 bits. First disable paging. + */ + movl %cr0, %eax + andl $~X86_CR0_PG, %eax + movl %eax, %cr0 + + /* Invalidate TLB */ + xorl %eax, %eax + movl %eax, %cr3 + + /* Disable Long mode in EFER (Extended Feature Enable Register) */ + movl $MSR_EFER, %ecx + rdmsr + btr $_EFER_LME, %eax + wrmsr + + /* Set up table pointer for _x86boot_start */ + mov %ebx, %ecx + + /* Jump to the required target */ + pushl %edi /* 32-bit code segment */ + pushl %esi /* 32-bit target address */ + retf |