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chainload: BIOS: do not rely on 0x7c00 being free

This commit is contained in:
mintsuki 2023-03-07 13:07:28 +01:00
parent 39784a2199
commit 6523b0bc4e
1 changed files with 15 additions and 5 deletions
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20
common/protos/chainload.c
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@ -21,7 +21,7 @@
#if defined (BIOS)
__attribute__((noinline, section(".realmode")))
noreturn static void spinup(uint8_t drive) {
noreturn static void spinup(uint8_t drive, void *buf) {
struct idtr real_mode_idt;
real_mode_idt.limit = 0x3ff;
real_mode_idt.ptr = 0;
@ -30,6 +30,14 @@ noreturn static void spinup(uint8_t drive) {
"cli\n\t"
"cld\n\t"
// Safe stack location
"mov $0x7c00, %%esp\n\t"
// move buffer to final location
"mov $0x7c00, %%edi\n\t"
"mov $512, %%ecx\n\t"
"rep movsb\n\t"
"lidt (%%eax)\n\t"
"pushl $0x08\n\t"
@ -65,7 +73,7 @@ noreturn static void spinup(uint8_t drive) {
".code32\n\t"
:
: "a" (&real_mode_idt), "d" (drive)
: "a" (&real_mode_idt), "d" (drive), "S"(buf)
: "memory"
);
@ -177,15 +185,17 @@ load:
void bios_chainload_volume(struct volume *p) {
vga_textmode_init(false);
volume_read(p, (void *)0x7c00, 0, 512);
void *buf = ext_mem_alloc(512);
volatile uint16_t *boot_sig = (volatile uint16_t *)0x7dfe;
volume_read(p, buf, 0, 512);
uint16_t *boot_sig = (uint16_t *)(buf + 0x1fe);
if (*boot_sig != 0xaa55) {
return;
}
spinup(p->drive);
spinup(p->drive, buf);
}
#elif defined (UEFI)