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Got BIOS downcalls from Prot32 working

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This commit is contained in:
Thomas Oltmann 2026-02-21 14:13:24 +01:00
parent 0c14013b9d
commit c1737c30b7
2 changed files with 32 additions and 6 deletions
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12
src/bios.S
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@ -87,6 +87,9 @@ bios_func: push %ebp
// To support any interrupt number, we use self-modifying code.
mov %al, _bf_int+1
PROT16
REAL
mov 0(%edi), %eax
mov 4(%edi), %ecx
mov 8(%edi), %edx
@ -95,17 +98,11 @@ bios_func: push %ebp
mov 20(%edi), %esi
mov 24(%edi), %edi
PROT16
REAL
// This instruction will get written at runtime
_bf_int: .byte 0xCD, 0 // INT imm8
push $0
pushf
PROT
PROT32
push %edi
mov 8+4(%ebp), %edi
mov %eax, 0(%edi)
@ -117,6 +114,9 @@ _bf_int: .byte 0xCD, 0 // INT imm8
pop %eax
mov %eax, 24(%edi)
PROT
PROT32
pop %eax
pop %esi

26
src/main.c
View file

@ -51,6 +51,28 @@ struct vesa_info {
extern uint16_t bios_func(uint8_t inum, uint32_t reg[]);
#define PG_PRESENT 0x001
#define PG_WRITE 0x002
#define PG_USER 0x004
#define PG_SIZE 0x080
#define PG_GLOBAL 0x100
__attribute__((aligned(4096))) uint64_t pml4[512];
__attribute__((aligned(4096))) uint64_t pdp[512];
__attribute__((aligned(4096))) uint64_t pd[512];
uint64_t
pg_setup()
{
pml4[0] = (uint64_t)(uint32_t)pdp | PG_WRITE | PG_PRESENT;
pdp[0] = (uint64_t)(uint32_t)pd | PG_WRITE | PG_PRESENT;
for (unsigned i = 0; i < 512; i++) {
pd[i] = (i * (uint64_t)0x200000) | PG_WRITE | PG_PRESENT | PG_SIZE;
}
uint64_t cr3 = (uint64_t)(uint32_t)pml4;
return cr3;
}
void
main()
{
@ -72,6 +94,8 @@ main()
bios_write(buf);
}
pg_setup();
#if 0
char foo[24];
@ -109,6 +133,8 @@ main()
reg[6] = 0;
bios_func(0x10, reg);
bios_write("what?\r\n");
for (;;) {
__asm__ ("hlt");
}