mirror of
https://github.com/jart/cosmopolitan.git
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4631d34d0d
It's now possible to use sigaltstack() to recover from stack overflows on Windows. Several bugs in sigaltstack() have been fixed, for all our supported platforms. There's a newer better example showing how to use this, along with three independent unit tests just to further showcase the various techniques.
127 lines
4.9 KiB
C
127 lines
4.9 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2023 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/assert.h"
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#include "libc/calls/struct/rlimit.h"
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#include "libc/calls/struct/rlimit.internal.h"
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#include "libc/dce.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/macros.internal.h"
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#include "libc/runtime/runtime.h"
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#include "libc/runtime/stack.h"
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#include "libc/sysv/consts/auxv.h"
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#include "libc/sysv/consts/rlim.h"
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#include "libc/sysv/consts/rlimit.h"
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// Hack for guessing boundaries of _start()'s stack
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//
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// Every UNIX system in our support vector creates arg blocks like:
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//
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// <HIGHEST-STACK-ADDRESS>
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// last environ string
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// ...
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// first environ string
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// ...
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// auxiliary value pointers
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// environ pointers
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// argument pointers
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// argument count
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// --- %rsp _start()
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// ...
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// ...
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// ... program's stack
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// ...
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// ...
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// <LOWEST-STACK-ADDRESS>
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//
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// The region of memory between highest and lowest can be computed
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// across all supported platforms ±1 page accuracy as the distance
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// between the last character of the last environ variable rounded
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// up to the microprocessor page size (this computes the top addr)
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// and the bottom is computed by subtracting RLIMIT_STACK rlim_cur
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// It's simple but gets tricky if we consider environ can be empty
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//
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// This code always guesses correctly on Windows because WinMain()
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// is written to allocate a stack ourself. Local testing on Linux,
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// XNU, FreeBSD, OpenBSD, and NetBSD says that accuracy is ±1 page
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// and that error rate applies to both beginning and end addresses
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static char *__get_last(char **list) {
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char *res = 0;
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for (int i = 0; list[i]; ++i) {
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res = list[i];
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}
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return res;
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}
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static int __get_length(const char *s) {
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int n = 0;
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while (*s++) ++n;
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return n;
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}
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static uintptr_t __get_main_top(int pagesz) {
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uintptr_t top;
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const char *s;
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if ((s = __get_last(__envp)) || (s = __get_last(__argv))) {
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top = (uintptr_t)s + __get_length(s);
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} else {
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unsigned long *xp = __auxv;
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while (*xp) xp += 2;
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top = (uintptr_t)xp;
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}
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return ROUNDUP(top, pagesz);
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}
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static size_t __get_stack_size(int pagesz, uintptr_t start, uintptr_t top) {
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size_t size, max = 8 * 1024 * 1024;
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struct rlimit rlim = {RLIM_INFINITY};
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sys_getrlimit(RLIMIT_STACK, &rlim);
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if ((size = rlim.rlim_cur) > max) size = max;
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return MAX(ROUNDUP(size, pagesz), ROUNDUP(top - start, pagesz));
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}
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/**
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* Returns approximate boundaries of main thread stack.
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*/
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void __get_main_stack(void **out_addr, size_t *out_size, int *out_guardsize) {
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if (IsWindows()) {
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*out_addr = (void *)GetStaticStackAddr(0);
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*out_size = GetStaticStackSize();
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*out_guardsize = GetGuardSize();
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return;
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}
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int pagesz = getauxval(AT_PAGESZ);
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uintptr_t start = (uintptr_t)__argv;
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uintptr_t top = __get_main_top(pagesz);
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uintptr_t bot = top - __get_stack_size(pagesz, start, top);
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uintptr_t vdso = getauxval(AT_SYSINFO_EHDR);
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if (vdso) {
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if (vdso > start && vdso < top) {
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top = vdso;
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} else if (vdso < start && vdso >= bot) {
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bot += vdso + pagesz * 2;
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}
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}
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unassert(bot < top);
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unassert(bot < start);
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unassert(top > start);
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*out_addr = (void *)bot;
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*out_size = top - bot;
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*out_guardsize = pagesz;
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}
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