libucontext/arch/x86/swapcontext.S

73 lines
2.1 KiB
ArmAsm

/*
* Copyright (c) 2018, 2020 Ariadne Conill <ariadne@dereferenced.org>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* This software is provided 'as is' and without any warranty, express or
* implied. In no event shall the authors be liable for any damages arising
* from the use of this software.
*/
#include "defs.h"
ALIAS(swapcontext, __swapcontext)
FUNC(__swapcontext)
/* load address of the ucontext structure */
movl 4(%esp), %eax
/* EAX is not a preserved register */
movl $0, REG_OFFSET(REG_EAX)(%eax)
/* copy all of the current registers into the ucontext structure */
movl %ecx, REG_OFFSET(REG_ECX)(%eax)
movl %ebx, REG_OFFSET(REG_EBX)(%eax)
movl %edx, REG_OFFSET(REG_EDX)(%eax)
movl %edi, REG_OFFSET(REG_EDI)(%eax)
movl %esi, REG_OFFSET(REG_ESI)(%eax)
movl %ebp, REG_OFFSET(REG_EBP)(%eax)
/* the first argument on the stack is the jump target (%eip), so we store it in the EIP
register in the ucontext structure. */
movl (%esp), %ecx
movl %ecx, REG_OFFSET(REG_EIP)(%eax)
/* take the stack pointer address (%esp) offsetting by 4 to skip over the jump target. */
leal 4(%esp), %ecx
movl %ecx, REG_OFFSET(REG_ESP)(%eax)
/* finally, save the FS segment register */
xorl %ecx, %ecx
movw %fs, %cx
movl %ecx, REG_OFFSET(REG_FS)(%eax)
/* load address of the ucontext structure */
movl 8(%esp), %eax
/* set up the FS segment register */
movl REG_OFFSET(REG_FS)(%eax), %ecx
movw %cx, %fs
/* fetch the new EIP */
movl REG_OFFSET(REG_EIP)(%eax), %ecx
/* set up the new stack pointer */
movl REG_OFFSET(REG_ESP)(%eax), %esp
/* push the return address onto the stack */
pushl %ecx
/* set all of the registers */
movl REG_OFFSET(REG_EBX)(%eax), %ebx
movl REG_OFFSET(REG_ECX)(%eax), %ecx
movl REG_OFFSET(REG_EDX)(%eax), %edx
movl REG_OFFSET(REG_EBP)(%eax), %ebp
movl REG_OFFSET(REG_EDI)(%eax), %edi
movl REG_OFFSET(REG_ESI)(%eax), %esi
movl REG_OFFSET(REG_EAX)(%eax), %eax
ret
END(__swapcontext)