Ignore SEGV during profiler unwind on Unix (#28291)

src/signals-unix.c

@@ -89,6 +89,14 @@ static void jl_call_in_ctx(jl_ptls_t ptls, void (*fptr)(void), int sig, void *_c
     // checks that the syscall is made in the signal handler and that
     // the ucontext address is valid. Hopefully the value of the ucontext
     // will not be part of the validation...
+    if (!ptls->signal_stack) {
+        sigset_t sset;
+        sigemptyset(&sset);
+        sigaddset(&sset, sig);
+        sigprocmask(SIG_UNBLOCK, &sset, NULL);
+        fptr();
+        return;
+    }
     uintptr_t rsp = (uintptr_t)ptls->signal_stack + sig_stack_size;
     assert(rsp % 16 == 0);
 #if defined(_OS_LINUX_) && defined(_CPU_X86_64_)
@@ -667,9 +675,22 @@ static void *signal_listener(void *arg)
             // do backtrace for profiler
             if (profile && running) {
                 if (bt_size_cur < bt_size_max - 1) {
-                    // Get backtrace data
-                    bt_size_cur += rec_backtrace_ctx((uintptr_t*)bt_data_prof + bt_size_cur,
-                            bt_size_max - bt_size_cur - 1, signal_context);
+                    // unwinding can fail, so keep track of the current state
+                    // and restore from the SEGV handler if anything happens.
+                    jl_ptls_t ptls = jl_get_ptls_states();
+                    jl_jmp_buf *old_buf = ptls->safe_restore;
+                    jl_jmp_buf buf;
+
+                    ptls->safe_restore = &buf;
+                    if (jl_setjmp(buf, 0)) {
+                        jl_safe_printf("WARNING: profiler attempt to access an invalid memory location\n");
+                    } else {
+                        // Get backtrace data
+                        bt_size_cur += rec_backtrace_ctx((uintptr_t*)bt_data_prof + bt_size_cur,
+                                bt_size_max - bt_size_cur - 1, signal_context);
+                    }
+                    ptls->safe_restore = old_buf;
+
                     // Mark the end of this block with 0
                     bt_data_prof[bt_size_cur++] = 0;
                 }