04cb6b3aa6
ABI-required stack alignment. C code expects that the push of the return address disturbed the 16 byte alignment and it will take corrective measures to fix it before making another call. Of course, if its wrong to start with, then all hell breaks loose. Essentially we "fix" this by making the stack alignment odd to start with. This was one of the things that broke on libkse with apps that use floating point/varargs/etc. Approved by: re (scottl)
108 lines
3.5 KiB
C
108 lines
3.5 KiB
C
/*
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* Copyright (c) 2003 Marcel Moolenaar
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/ucontext.h>
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#include <stdarg.h>
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#include <stdlib.h>
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typedef void (*func_t)(uint64_t, uint64_t, uint64_t, uint64_t, uint64_t,
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uint64_t);
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/* Prototypes */
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static void ctx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args);
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__weak_reference(__makecontext, makecontext);
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void
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__makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
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{
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uint64_t *args;
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uint64_t *sp;
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va_list ap;
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int i;
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/* A valid context is required. */
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if ((ucp == NULL) || (ucp->uc_mcontext.mc_len != sizeof(mcontext_t)))
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return;
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else if ((argc < 0) || (argc > 6) || (ucp->uc_stack.ss_sp == NULL) ||
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(ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
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/*
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* This should really return -1 with errno set to ENOMEM
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* or something, but the spec says that makecontext is
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* a void function. At least make sure that the context
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* isn't valid so it can't be used without an error.
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*/
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ucp->uc_mcontext.mc_len = 0;
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return;
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}
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/* Align the stack to 16 bytes. */
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sp = (uint64_t *)(ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
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sp = (uint64_t *)((uint64_t)sp & -15UL);
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/* Allocate space for a maximum of 6 arguments on the stack. */
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args = sp - 6;
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/*
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* Account for arguments on stack and do the funky C entry alignment.
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* This means that we need an 8-byte-odd alignment since the ABI expects
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* the return address to be pushed, thus breaking the 16 byte alignment.
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*/
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sp -= 7;
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/* Add the arguments: */
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va_start(ap, argc);
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for (i = 0; i < argc; i++)
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args[i] = va_arg(ap, uint64_t);
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va_end(ap);
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for (i = argc; i < 6; i++)
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args[i] = 0;
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ucp->uc_mcontext.mc_rdi = (register_t)ucp;
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ucp->uc_mcontext.mc_rsi = (register_t)start;
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ucp->uc_mcontext.mc_rdx = (register_t)args;
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ucp->uc_mcontext.mc_rbp = (register_t)sp;
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ucp->uc_mcontext.mc_rbx = (register_t)sp;
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ucp->uc_mcontext.mc_rsp = (register_t)sp;
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ucp->uc_mcontext.mc_rip = (register_t)ctx_wrapper;
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}
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static void
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ctx_wrapper(ucontext_t *ucp, func_t func, uint64_t *args)
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{
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(*func)(args[0], args[1], args[2], args[3], args[4], args[5]);
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if (ucp->uc_link == NULL)
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exit(0);
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setcontext((const ucontext_t *)ucp->uc_link);
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/* should never get here */
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abort();
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/* NOTREACHED */
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}
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