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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.
110 lines
3.7 KiB
C
110 lines
3.7 KiB
C
#if 0
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/*─────────────────────────────────────────────────────────────────╗
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│ To the extent possible under law, Justine Tunney has waived │
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│ all copyright and related or neighboring rights to this file, │
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│ as it is written in the following disclaimers: │
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│ • http://unlicense.org/ │
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│ • http://creativecommons.org/publicdomain/zero/1.0/ │
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╚─────────────────────────────────────────────────────────────────*/
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#endif
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#include "libc/calls/struct/sigaction.h"
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#include "libc/calls/struct/sigaltstack.h"
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#include "libc/calls/struct/siginfo.h"
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#include "libc/calls/struct/ucontext.internal.h"
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#include "libc/calls/ucontext.h"
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#include "libc/intrin/kprintf.h"
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#include "libc/limits.h"
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#include "libc/mem/gc.internal.h"
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#include "libc/mem/mem.h"
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#include "libc/runtime/runtime.h"
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#include "libc/runtime/sysconf.h"
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#include "libc/sysv/consts/sa.h"
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#include "libc/sysv/consts/sig.h"
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#include "libc/sysv/consts/ss.h"
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#include "libc/testlib/testlib.h"
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#include "libc/thread/thread.h"
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/**
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* stack overflow recovery technique #3
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* rewrite thread cpu state to call pthread_exit
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* this method returns gracefully from signal handlers
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* unfortunately it relies on cpu architecture knowledge
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*
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* @see test/libc/thread/stackoverflow1_test.c
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* @see test/libc/thread/stackoverflow2_test.c
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* @see test/libc/thread/stackoverflow3_test.c
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*/
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volatile bool smashed_stack;
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void Exiter(void *rc) {
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struct sigaltstack ss;
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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ASSERT_EQ(0, ss.ss_flags);
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pthread_exit(rc);
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}
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void CrashHandler(int sig, siginfo_t *si, void *arg) {
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ucontext_t *ctx = arg;
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struct sigaltstack ss;
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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ASSERT_EQ(SS_ONSTACK, ss.ss_flags);
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kprintf("kprintf avoids overflowing %G %p\n", si->si_signo, si->si_addr);
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smashed_stack = true;
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ASSERT_TRUE(__is_stack_overflow(si, ctx));
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//
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// the backtrace will look like this
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//
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// 0x000000000042561d: pthread_exit at pthread_exit.c:99
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// 0x0000000000418777: Exiter at stackoverflow2_test.c:40
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// 0x00000000004186d8: CrashHandler at stackoverflow2_test.c:49
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// 0x000000000041872a: StackOverflow at stackoverflow2_test.c:53
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// 0x000000000041872a: StackOverflow at stackoverflow2_test.c:53
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// 0x000000000041872a: StackOverflow at stackoverflow2_test.c:53
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// ...
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//
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ctx->uc_mcontext.ARG0 = 123;
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ctx->uc_mcontext.PC = (long)Exiter;
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ctx->uc_mcontext.SP += 32768;
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ctx->uc_mcontext.SP &= -16;
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ctx->uc_mcontext.SP -= 8;
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}
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int StackOverflow(int f(), int n) {
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if (n < INT_MAX) {
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return f(f, n + 1) - 1;
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} else {
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return INT_MAX;
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}
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}
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int (*pStackOverflow)(int (*)(), int) = StackOverflow;
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void *MyPosixThread(void *arg) {
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struct sigaction sa;
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struct sigaltstack ss;
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ss.ss_flags = 0;
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ss.ss_size = sysconf(_SC_MINSIGSTKSZ) + 4096;
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ss.ss_sp = gc(malloc(ss.ss_size));
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ASSERT_SYS(0, 0, sigaltstack(&ss, 0));
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sa.sa_flags = SA_SIGINFO | SA_ONSTACK; // <-- important
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sigemptyset(&sa.sa_mask);
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sa.sa_sigaction = CrashHandler;
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sigaction(SIGBUS, &sa, 0);
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sigaction(SIGSEGV, &sa, 0);
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exit(pStackOverflow(pStackOverflow, 0));
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return 0;
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}
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int main(int argc, char *argv[]) {
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void *res;
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pthread_t th;
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struct sigaltstack ss;
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smashed_stack = false;
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pthread_create(&th, 0, MyPosixThread, 0);
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pthread_join(th, &res);
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ASSERT_EQ((void *)123L, res);
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ASSERT_TRUE(smashed_stack);
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ASSERT_SYS(0, 0, sigaltstack(0, &ss));
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ASSERT_EQ(SS_DISABLE, ss.ss_flags);
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}
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