Backup and restore %eax only around code that needs to use %eax.
Signed-off-by: Kevin O'Connor kevin@koconnor.net --- src/romlayout.S | 89 ++++++++++++++++++++++++++------------------------------- 1 file changed, 40 insertions(+), 49 deletions(-)
diff --git a/src/romlayout.S b/src/romlayout.S index 7938e22..d78737b 100644 --- a/src/romlayout.S +++ b/src/romlayout.S @@ -22,18 +22,13 @@ // %edx = return location (in 32bit mode) // Clobbers: ecx, flags, segment registers, cr0, idt/gdt DECLFUNC transition32 -transition32_nmi_off: - // transition32 when NMI and A20 are already initialized - movl %eax, %ecx - jmp 1f transition32: - movl %eax, %ecx - // Disable irqs (and clear direction flag) cli cld
// Disable nmi + movl %eax, %ecx movl $CMOS_RESET_CODE|NMI_DISABLE_BIT, %eax outb %al, $PORT_CMOS_INDEX inb $PORT_CMOS_DATA, %al @@ -42,29 +37,30 @@ transition32: inb $PORT_A20, %al orb $A20_ENABLE_BIT, %al outb %al, $PORT_A20 + movl %ecx, %eax
+transition32_nmi_off: // Set segment descriptors -1: lidtw %cs:pmode_IDT_info + lidtw %cs:pmode_IDT_info lgdtw %cs:rombios32_gdt_48
// Enable protected mode - movl %cr0, %eax - orl $CR0_PE, %eax - movl %eax, %cr0 + movl %cr0, %ecx + orl $CR0_PE, %ecx + movl %ecx, %cr0
// start 32bit protected mode code - ljmpl $SEG32_MODE32_CS, $(BUILD_BIOS_ADDR + 2f) + ljmpl $SEG32_MODE32_CS, $(BUILD_BIOS_ADDR + 1f)
.code32 // init data segments -2: movl $SEG32_MODE32_DS, %eax - movw %ax, %ds - movw %ax, %es - movw %ax, %ss - movw %ax, %fs - movw %ax, %gs +1: movl $SEG32_MODE32_DS, %ecx + movw %cx, %ds + movw %cx, %es + movw %cx, %ss + movw %cx, %fs + movw %cx, %gs
- movl %ecx, %eax jmpl *%edx .code16
@@ -75,61 +71,56 @@ transition32: .global transition16big .code32 transition16: - movl %eax, %ecx - - // restore data segment limits to 0xffff - movl $SEG32_MODE16_DS, %eax - movw %ax, %ds - movw %ax, %es - movw %ax, %ss - movw %ax, %fs - movw %ax, %gs - #if CONFIG_DISABLE_A20 // disable a20 + movl %eax, %ecx inb $PORT_A20, %al andb $~A20_ENABLE_BIT, %al outb %al, $PORT_A20 + movl %ecx, %eax #endif
+ // Reset data segment limits + movl $SEG32_MODE16_DS, %ecx + movw %cx, %ds + movw %cx, %es + movw %cx, %ss + movw %cx, %fs + movw %cx, %gs + // Jump to 16bit mode ljmpw $SEG32_MODE16_CS, $1f
transition16big: - movl %eax, %ecx - - movl $SEG32_MODE16BIG_DS, %eax - movw %ax, %ds - movw %ax, %es - movw %ax, %ss - movw %ax, %fs - movw %ax, %gs + movl $SEG32_MODE16BIG_DS, %ecx + movw %cx, %ds + movw %cx, %es + movw %cx, %ss + movw %cx, %fs + movw %cx, %gs
ljmpw $SEG32_MODE16BIG_CS, $1f
.code16 -1: // Disable protected mode - movl %cr0, %eax - andl $~CR0_PE, %eax - movl %eax, %cr0 +1: movl %cr0, %ecx + andl $~CR0_PE, %ecx + movl %ecx, %cr0
// far jump to flush CPU queue after transition to real mode ljmpw $SEG_BIOS, $2f
-2: // restore IDT to normal real-mode defaults - lidtw %cs:rmode_IDT_info +2: lidtw %cs:rmode_IDT_info
// Clear segment registers - xorw %ax, %ax - movw %ax, %fs - movw %ax, %gs - movw %ax, %es - movw %ax, %ds - movw %ax, %ss // Assume stack is in segment 0 + xorw %cx, %cx + movw %cx, %fs + movw %cx, %gs + movw %cx, %es + movw %cx, %ds + movw %cx, %ss // Assume stack is in segment 0
- movl %ecx, %eax jmpl *%edx
-
Kevin O'Connor