Catch writes to protected memory in mmapped arrays (fix #3434)

Author: timholy

src/init.c

@@ -140,12 +140,18 @@ void segv_handler(int sig, siginfo_t *info, void *context)
 {
     sigset_t sset;
 
-    if (in_jl_ || is_addr_on_stack(info->si_addr)) {
+    if (in_jl_ || is_addr_on_stack(info->si_addr)) {  // stack overflow
         sigemptyset(&sset);
         sigaddset(&sset, SIGSEGV);
         sigprocmask(SIG_UNBLOCK, &sset, NULL);
         jl_throw(jl_stackovf_exception);
     }
+    else if (info->si_code == SEGV_ACCERR) {  // writing to read-only memory (e.g., mmap)
+        sigemptyset(&sset);
+        sigaddset(&sset, SIGSEGV);
+        sigprocmask(SIG_UNBLOCK, &sset, NULL);
+        jl_throw(jl_memory_exception);
+    }
     else {
         uv_tty_reset_mode();
         sigfillset(&sset);

test/file.jl

@@ -138,6 +138,7 @@ c = mmap_array(Uint8, (11,), s)
 @test c == "Hello World".data
 c = mmap_array(Uint8, (uint16(11),), s)
 @test c == "Hello World".data
+@test_throws MemoryError c[1] = 0   # read-only memory
 @test_throws ErrorException mmap_array(Uint8, (int16(-11),), s)
 @test_throws ErrorException mmap_array(Uint8, (typemax(Uint),), s)
 close(s)