libucontext/arch/x86_64/makecontext.c

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2018-01-30 03:41:02 +00:00
/*
* Copyright (c) 2018 William Pitcock <nenolod@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.
*/
#define _GNU_SOURCE
#include <stddef.h>
#include <stdarg.h>
#include <signal.h>
#include <string.h>
#include <stdint.h>
extern void __start_context(void);
void
__makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
{
greg_t *sp;
va_list va;
int i;
unsigned int uc_link;
uc_link = (argc > 6 ? argc - 6 : 0) + 1;
sp = (greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
sp -= uc_link;
sp = (greg_t *) (((uintptr_t) sp & -16L) - 8);
ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t) func;
ucp->uc_mcontext.gregs[REG_RBX] = (uintptr_t) &sp[uc_link];
ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp;
sp[0] = (uintptr_t) &__start_context;
sp[uc_link] = (uintptr_t) ucp->uc_link;
va_start(va, argc);
for (i = 0; i < argc; i++)
switch (i)
{
case 0:
ucp->uc_mcontext.gregs[REG_RDI] = va_arg (va, greg_t);
break;
case 1:
ucp->uc_mcontext.gregs[REG_RSI] = va_arg (va, greg_t);
break;
case 2:
ucp->uc_mcontext.gregs[REG_RDX] = va_arg (va, greg_t);
break;
case 3:
ucp->uc_mcontext.gregs[REG_RCX] = va_arg (va, greg_t);
break;
case 4:
ucp->uc_mcontext.gregs[REG_R8] = va_arg (va, greg_t);
break;
case 5:
ucp->uc_mcontext.gregs[REG_R9] = va_arg (va, greg_t);
break;
default:
sp[i - 5] = va_arg (va, greg_t);
break;
}
va_end(va);
}
extern __typeof(__makecontext) makecontext __attribute__((weak, __alias__("__makecontext")));