bios.call: clean and avoid hardcoding the gdt and idt when returning to long mode

Do not make assumptions on the previous gdt and idt, as well as the state of the flags
when operating.

1 files changed, 39 insertions, 42 deletions

diff --git a/rt/+x86_64/realcall.S b/rt/+x86_64/realcall.S
index 9e9afb4..ffbc0a9 100644
--- a/rt/+x86_64/realcall.S
+++ b/rt/+x86_64/realcall.S
@@ -14,18 +14,13 @@ redi:
 	.int 0x0
 resi:
 	.int 0x0
-rds:
-	.short 0x0
 res:
 	.short 0x0
-rss:
-	.short 0x0
-rgs:
-	.short 0x0
-rfs:
-	.short 0x0
-
 
+prev_idt:
+	.quad 0x0
+prev_gdt:
+	.quad 0x0
 
 # :real_call
 # This function is intended to be called from long mode
@@ -45,12 +40,25 @@ bios.call:
 	push %r13
 	push %r14
 	push %r15
+	pushf
+
+	# :Save code segment (and second push to prepare for far return)
+	mov %cs, %ax
+	push %ax
+	push %ax
+
+	# :Save data segment
+	mov %ds, %ax
+	push %ax
+	# :Save the interrupt number
 	push %di
 
 	cli
 
+	sidt (prev_idt)
+	sgdt (prev_gdt)
 
-	lgdt gdtr32
+	lgdt (gdtr32)
 	pushq $(gdt32_code - gdt32)
 	pushq $real_call_to_pmode_down
 	retfq
@@ -92,15 +100,12 @@ real_call_to_16bits_rmode_down:
 	mov %ax, %fs
 
 	lidt bios_idtr
-	sti
 
 	# :Self modifying code to call arbitrary interrupts
 	pop %ax
 	mov $real_call_int, %bx
 	mov %al, 1(%bx)
 
-	push %ds
-
 	# :Load registers
 	mov (reax), %eax
 	mov (rebx), %ebx
@@ -108,29 +113,22 @@ real_call_to_16bits_rmode_down:
 	mov (redx), %edx
 	mov (redi), %edi
 	mov (resi), %esi
-	mov %ds:(res), %es
-	mov %ds:(rss), %ss
-	mov %ds:(rgs), %gs
-	mov %ds:(rfs), %fs
-	mov %ds:(rds), %ds
-	xchg %bx, %bx
+	mov (res), %es
+
+	sti
 
 real_call_int:
 	int $0x0
-	
-	pop %ds
-	mov %ds:(rfs), %fs
-	mov %ds:(rgs), %gs
-	mov %ds:(rss), %ss
-	mov %ds:(res), %es
+
+	cli
+
+	mov %es, (res)
 	mov %eax, (reax)
 	mov %ebx, (rebx)
 	mov %ecx, (recx)
 	mov %edx, (redx)
 	mov %edi, (redi)
 	mov %esi, (resi)
-
-	cli
 	
 	# :Restore protected mode
 	mov %cr0, %eax
@@ -157,33 +155,32 @@ real_call_to_pmode_up:
 	or $1 << 31, %eax
 	mov %eax, %cr0
 
-	lgdt gdtr64
-	ljmp $(gdt64_code - gdt64), $real_call_to_longmode_up
+	lgdt (prev_gdt)
+
+	# :At this point %ds is latest in stack
+	pop %ax
+
+	# :At this point %cs is latest in stack
+	# Do a long jump
+	push $real_call_to_longmode_up
+	retf
 .code64
 real_call_to_longmode_up:
-	mov $(gdt64_data - gdt64), %ax
 	mov %ax, %fs
 	mov %ax, %gs
 	mov %ax, %ss
 	mov %ax, %es
 	mov %ax, %ds
 
+	# :Avoid doing this until the bootloader loads a 64 bits IDT
+	# XXX
+	#idt (prev_idt)
+
 real_call_end:
+	popf
 	pop %r15
 	pop %r14
 	pop %r13
 	pop %r12
 	pop %rbx
 	ret
-
-.globl testt
-testt:
-	mov $1, %al
-	mov $0x43, %bh
-	mov $0x6, %ah
-	mov $0, %ch
-	mov $0, %cl
-	mov $5, %dh
-	mov $5, %dl
-	int $0x10
-	ret