1 files changed, 75 insertions, 0 deletions
diff --git a/third_party/nix/src/libmain/stack.cc b/third_party/nix/src/libmain/stack.cc
new file mode 100644
index 000000000000..628b6313a89c
--- /dev/null
+++ b/third_party/nix/src/libmain/stack.cc
@@ -0,0 +1,75 @@
+#include <csignal>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+
+#include <unistd.h>
+
+#include "libutil/types.hh"
+
+namespace nix {
+
+static void sigsegvHandler(int signo, siginfo_t* info, void* ctx) {
+  /* Detect stack overflows by comparing the faulting address with
+     the stack pointer.  Unfortunately, getting the stack pointer is
+     not portable. */
+  bool haveSP = true;
+  char* sp = nullptr;
+#if defined(__x86_64__) && defined(REG_RSP)
+  sp = (char*)(static_cast<ucontext_t*>(ctx))->uc_mcontext.gregs[REG_RSP];
+#elif defined(REG_ESP)
+  sp = (char*)((ucontext_t*)ctx)->uc_mcontext.gregs[REG_ESP];
+#else
+  haveSP = false;
+#endif
+
+  if (haveSP) {
+    ptrdiff_t diff = static_cast<char*>(info->si_addr) - sp;
+    if (diff < 0) {
+      diff = -diff;
+    }
+    if (diff < 4096) {
+      char msg[] = "error: stack overflow (possible infinite recursion)\n";
+      [[gnu::unused]] auto res = write(2, msg, strlen(msg));
+      _exit(1);  // maybe abort instead?
+    }
+  }
+
+  /* Restore default behaviour (i.e. segfault and dump core). */
+  struct sigaction act;
+  sigfillset(&act.sa_mask);
+  act.sa_handler = SIG_DFL;
+  act.sa_flags = 0;
+  if (sigaction(SIGSEGV, &act, nullptr) != 0) {
+    abort();
+  }
+}
+
+void detectStackOverflow() {
+#if defined(SA_SIGINFO) && defined(SA_ONSTACK)
+  /* Install a SIGSEGV handler to detect stack overflows.  This
+     requires an alternative stack, otherwise the signal cannot be
+     delivered when we're out of stack space. */
+  stack_t stack;
+  stack.ss_size = 4096 * 4 + MINSIGSTKSZ;
+  static auto stackBuf = std::make_unique<std::vector<char>>(stack.ss_size);
+  stack.ss_sp = stackBuf->data();
+  if (stack.ss_sp == nullptr) {
+    throw Error("cannot allocate alternative stack");
+  }
+  stack.ss_flags = 0;
+  if (sigaltstack(&stack, nullptr) == -1) {
+    throw SysError("cannot set alternative stack");
+  }
+
+  struct sigaction act;
+  sigfillset(&act.sa_mask);
+  act.sa_sigaction = sigsegvHandler;
+  act.sa_flags = SA_SIGINFO | SA_ONSTACK;
+  if (sigaction(SIGSEGV, &act, nullptr) != 0) {
+    throw SysError("resetting SIGSEGV");
+  }
+#endif
+}
+
+}  // namespace nix