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Fix real mode transition #294

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merged 3 commits into from
Aug 29, 2023
Merged

Fix real mode transition #294

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5cbaa52
real_mode: Fix long to protected mode transition
sktt Aug 29, 2023
b51ffb7
boot,unittest: re-enable real mode testing
sktt Aug 29, 2023
5c74317
asm-macros: SAVE_ALL_REGS32 in protected mode
sktt Aug 29, 2023
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4 changes: 4 additions & 0 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,10 @@ ifeq ($(CONFIG_ACPICA),y)
COMMON_FLAGS += -DKTF_ACPICA
endif

ifneq ($(UNITTEST),)
COMMON_FLAGS += -DKTF_UNIT_TEST
endif

AFLAGS := $(COMMON_FLAGS) -DASM_FILE -D__ASSEMBLY__ -nostdlib -nostdinc
CFLAGS := $(COMMON_FLAGS) -std=gnu99 -O2 -g -Wall -Wextra -ffreestanding -nostdlib -nostdinc
CFLAGS += -mno-red-zone -mno-mmx -mno-sse -mno-sse2
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22 changes: 12 additions & 10 deletions arch/x86/real_mode.S
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Expand Up @@ -139,7 +139,18 @@ END_FUNC(_prot_to_real)

.align 16
.Lfrom_long_mode:
/* Disable LME in EFER */
/* Use protected mode data segment */
mov $__KERN_DS32, %eax
mov %eax, %ds
mov %eax, %ss

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/* Disable paging to enter protected mode. */
/* Clearing PG implicitly clears EFER.LMA, see Intel SDM 9.8.5.4, */
mov %cr0, %eax
and $~(X86_CR0_PG | X86_CR0_WP), %eax
mov %eax, %cr0

/* Disable LME in EFER. */
movl $MSR_EFER, %ecx
rdmsr
and $~EFER_LME, %eax
Expand All @@ -151,15 +162,6 @@ END_FUNC(_prot_to_real)
lgdt rmode_gdt_ptr
lidt rmode_idt_ptr

/* Disable paging to enter protected mode */
mov %cr0, %eax
and $~(X86_CR0_PG | X86_CR0_WP), %eax
mov %eax, %cr0

/* Use protected mode data selector */
mov $__KERN_DS32, %eax
mov %eax, %ds

/* Use real mode accessible stack */
mov rmode_stack, %esp

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42 changes: 27 additions & 15 deletions include/arch/x86/asm-macros.h
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Expand Up @@ -69,27 +69,33 @@
.endm

.macro SAVE_ALL_REGS32
push %eax
push %ebx
push %ecx
push %edx
push %esi
push %edi
push %ebp
.endm

.macro RESTORE_ALL_REGS32
pop %ebp
pop %edi
pop %esi
pop %edx
pop %ecx
pop %ebx
pop %eax
.endm

.macro SAVE_ALL_REGS
push %_ASM_AX
push %_ASM_BX
push %_ASM_CX
push %_ASM_DX
push %_ASM_SI
push %_ASM_DI
push %_ASM_BP
.endm

.macro RESTORE_ALL_REGS32
pop %_ASM_BP
pop %_ASM_DI
pop %_ASM_SI
pop %_ASM_DX
pop %_ASM_CX
pop %_ASM_BX
pop %_ASM_AX
.endm

.macro SAVE_ALL_REGS
SAVE_ALL_REGS32
#if defined(__x86_64__)
push %r8
push %r9
Expand All @@ -113,7 +119,13 @@
pop %r9
pop %r8
#endif
RESTORE_ALL_REGS32
pop %_ASM_BP
pop %_ASM_DI
pop %_ASM_SI
pop %_ASM_DX
pop %_ASM_CX
pop %_ASM_BX
pop %_ASM_AX
.endm

.macro SAVE_CALLEE_SAVED_REGS
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2 changes: 0 additions & 2 deletions tests/unittests.c
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Expand Up @@ -173,10 +173,8 @@ int unit_tests(void *_unused) {
schedule_task(task_user1, get_bsp_cpu());
schedule_task(task_user2, get_cpu(1));

#ifdef UNITTEST_LONGMODE
printk("Long mode to real mode transition:\n");
long_to_real();
#endif

return 0;
}