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* Copyright (C) 2014 René Kijewski <>
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
* @ingroup x86-multithreading
* @{
* @file
* @brief Coroutine helper functions.
* @author René Kijewski <>
* @}
#include <ucontext.h>
#include <stdarg.h>
int __attribute__((optimize("omit-frame-pointer"), no_instrument_function)) getcontext(ucontext_t *ucp)
__asm__ volatile ("pushf\n" :: "a"(ucp));
__asm__ volatile ("pop 4*2(%eax)\n");
__asm__ volatile ("mov %eax, 4*3(%eax)\n");
__asm__ volatile ("mov %ecx, 4*4(%eax)\n");
__asm__ volatile ("mov %edx, 4*5(%eax)\n");
__asm__ volatile ("mov %ebx, 4*6(%eax)\n");
/* __asm__ volatile ("mov %esp, 4*7(%eax)\n"); omitted */
__asm__ volatile ("mov %ebp, 4*8(%eax)\n");
__asm__ volatile ("mov %esi, 4*9(%eax)\n");
__asm__ volatile ("mov %edi, 4*10(%eax)\n");
__asm__ volatile ("lea 4(%esp), %edx\n");
__asm__ volatile ("mov %edx, 4*0(%eax)\n");
__asm__ volatile ("xor %edx, %edx\n");
__asm__ volatile ("mov %edx, 4*1(%eax)\n");
__asm__ volatile ("mov (%esp), %edx\n");
__asm__ volatile ("mov %edx, 4*11(%eax)\n");
return 0;
int __attribute__((optimize("omit-frame-pointer"), no_instrument_function)) setcontext(const ucontext_t *ucp)
__asm__ volatile ("1:\n" :: "a"(ucp));
/* __asm__ volatile ("mov 4*3(%eax), %eax\n");, omitted */
__asm__ volatile ("mov 4*4(%eax), %ecx\n");
/* __asm__ volatile ("mov 4*5(%eax), %edx\n");, omitted */
__asm__ volatile ("mov 4*6(%eax), %ebx\n");
/* __asm__ volatile ("mov 4*7(%eax), %esp\n");, omitted */
__asm__ volatile ("mov 4*8(%eax), %ebp\n");
__asm__ volatile ("mov 4*9(%eax), %esi\n");
__asm__ volatile ("mov 4*10(%eax), %edi\n");
__asm__ volatile ("mov 4*0(%eax), %esp\n");
__asm__ volatile ("add 4*1(%eax), %esp\n");
__asm__ volatile ("mov 4*11(%eax), %edx\n");
__asm__ volatile ("mov %eax, %ebx\n");
__asm__ volatile ("push 4*2(%eax)\n");
__asm__ volatile ("popf\n");
__asm__ volatile ("call *%edx\n");
__asm__ volatile ("mov 4*12(%ebx), %eax\n");
__asm__ volatile ("jmp 1b\n");
static void __attribute__((optimize("omit-frame-pointer"), noreturn, no_instrument_function)) makecontext_entrypoint(void)
/* ebx = ucp, ecx = argc, ebp = arg[0], esi = arg[1], edi = arg[2] */
__asm__ volatile ("mov 4*3(%ebx), %eax\n"); /* eax = func */
__asm__ volatile ("jecxz 0f\n");
__asm__ volatile ("cmpb $1, %cl; je 1f\n");
__asm__ volatile ("cmpb $2, %cl; je 2f\n");
__asm__ volatile ("cmpb $3, %cl; je 3f\n");
__asm__ volatile ("cmpb $4, %cl; je 4f\n");
__asm__ volatile (" mov 4*7(%ebx), %edx; push %edx\n");
__asm__ volatile ("4: mov 4*5(%ebx), %edx; push %edx\n");
__asm__ volatile ("3: push %edi\n");
__asm__ volatile ("2: push %esi\n");
__asm__ volatile ("1: push %ebp\n");
__asm__ volatile ("0: call *%eax\n"); /* call func(...), preserves ebx */
__asm__ volatile ("mov 4*12(%ebx), %eax\n");
__asm__ volatile ("push %eax\n");
__asm__ volatile ("call setcontext\n");
void makecontext(ucontext_t *ucp, makecontext_fun_t func, int argc, ...)
ucp->uc_context.ip = (void *) (unsigned long) &makecontext_entrypoint;
ucp->uc_context.registers.bx = (unsigned long) ucp;
ucp-> = (unsigned long) func;
ucp-> = argc > 0 ? argc : 0;
if (argc <= 0) {
unsigned long *arg_registers[5] = {
va_list ap;
va_start(ap, argc);
for (int i = 0; i < argc; ++i) {
*arg_registers[i] = va_arg(ap, unsigned long);
int swapcontext(ucontext_t *oucp, const ucontext_t *ucp)
/* Valid sentinel: an address in .text section is not valid for a stack pointer. */
oucp->uc_context.registers.sp = (unsigned long) &swapcontext;
if (oucp->uc_context.registers.sp == (unsigned long) &swapcontext) {
oucp->uc_context.registers.sp = 0;
return 0;