[SOLVED] [Long mode] IRET causing page fault

[AlfaOmega08]

Do you have any idea of why the iret instruction causes a page fault with CR2 = 0xFFF8?

This is the handler code:

Code: Select all

	cld
	
	; Save the registers
	push rax
	push rcx
	push rdx
	push rbx
	push rbp
	push rsi
	push rdi	
	
	; Switch to the kernel data segment
	mov ax, 0x10
	mov ds, ax
	mov es, ax
	mov ss, ax
	
	; Push the pointer to the InterruptState object
	mov rdi, rsp
	
	; Call the C++ Code (Lymph::Hal::Idt::Manager::InterruptGlobalHandler)
	call _ZN5Astro3Hal3Idt7Manager22InterruptGlobalHandlerEP14InterruptStack

	mov rsp, rax

	pop rdi
	pop rsi
	pop rbp
	pop rbx
	pop rdx
	pop rcx
	pop rax
	
	; Remove the errorcode and the interrupt number from the stack
	add rsp, 0x10

	iret

This is the stack reported by bochs when iret gets executed:

Code: Select all

Stack address size 8
 | STACK 0xffffffff8010ef58 [0xffffffff:0x80208121]        <-- RIP
 | STACK 0xffffffff8010ef60 [0x00000000:0x00000008]        <-- CS
 | STACK 0xffffffff8010ef68 [0x00000000:0x00000286]        <-- RFLAGS
 | STACK 0xffffffff8010ef70 [0xffffffff:0x8010ef88]        <-- RSP
 | STACK 0xffffffff8010ef78 [0x00000000:0x00000010]        <-- SS
 | STACK 0xffffffff8010ef80 [0xffffffff:0x8020811c]        <-- some other rubbish
 | STACK 0xffffffff8010ef88 [0xffffffff:0x8010efb8]
 | STACK 0xffffffff8010ef90 [0xffffffff:0xc00011a0]

At the moment of IRET, RSP is containing a good value (0xffffffff8010ef58), so I can't imagine why it should throw a Page Fault... Any idea?

Thanks

[AlfaOmega08]

Ok, solved this... looking at the Intel manual 2A I noticed that IRET for long mode is IRETQ, as it needs the W opcode prefix. Just wondering why it isn't specified in the 3A manual

Thank you anyway