diff --git a/qemu/cputlb.c b/qemu/cputlb.c
index cde8e30e..ed120082 100644
--- a/qemu/cputlb.c
+++ b/qemu/cputlb.c
@@ -299,6 +299,11 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, target_ulong addr)
     if (unlikely(env1->tlb_table[mmu_idx][page_index].addr_code !=
                  (addr & TARGET_PAGE_MASK))) {
         cpu_ldub_code(env1, addr);
+        //check for NX related error from softmmu
+        if (env1->invalid_error == UC_ERR_MEM_READ) {
+            env1->invalid_error = UC_ERR_CODE_INVALID;
+            return -1;
+        }
     }
     pd = env1->iotlb[mmu_idx][page_index] & ~TARGET_PAGE_MASK;
     mr = iotlb_to_region(cpu->as, pd);
diff --git a/samples/Makefile b/samples/Makefile
index 72d1ca45..f6345ae8 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -99,6 +99,7 @@ SOURCES += sample_x86.c
 SOURCES += shellcode.c
 SOURCES += mem_unmap.c
 SOURCES += mem_protect.c
+SOURCES += mem_exec.c
 endif
 ifneq (,$(findstring m68k,$(UNICORN_ARCHS)))
 SOURCES += sample_m68k.c
@@ -113,7 +114,8 @@ all: $(BINARY)
 clean:
 	rm -rf *.o $(OBJS_ELF) $(BINARY) $(SAMPLEDIR)/*.exe $(SAMPLEDIR)/*.static $(OBJDIR)/lib$(LIBNAME)* $(OBJDIR)/$(LIBNAME)*
 	rm -rf libunicorn*.so libunicorn*.lib libunicorn*.dylib unicorn*.dll unicorn*.lib
-	rm -rf sample_x86 sample_arm sample_arm64 sample_mips sample_sparc sample_ppc sample_m68k shellcode mem_unmap mem_protect
+	rm -rf sample_x86 sample_arm sample_arm64 sample_mips sample_sparc sample_ppc sample_m68k \
+		shellcode mem_unmap mem_protect mem_exec
 
 $(BINARY): $(OBJS)
 
diff --git a/samples/mem_exec.c b/samples/mem_exec.c
new file mode 100644
index 00000000..b83ea7d0
--- /dev/null
+++ b/samples/mem_exec.c
@@ -0,0 +1,296 @@
+/*
+
+Executable memory regions demo / unit test
+
+Copyright(c) 2015 Chris Eagle
+
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+version 2 as published by the Free Software Foundation.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+
+*/
+
+#define __STDC_FORMAT_MACROS
+#include <inttypes.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#include <unicorn/unicorn.h>
+
+unsigned char PROGRAM[] =
+   "\xeb\x45\x5e\x81\xe6\x00\xf0\xff\xff\x40\x40\x40\x40\x40\x40\x40"
+   "\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40\x40"
+   "\x40\x40\x40\x40\x40\x40\x40\x89\xf7\x81\xc7\x00\x00\x10\x00\xb9"
+   "\x4c\x00\x00\x00\x81\xff\x00\x00\x40\x00\x75\x01\xf4\xf3\xa4\x81"
+   "\xe7\x00\xf0\xff\xff\xff\xe7\xe8\xb6\xff\xff\xff";
+// total size: 76 bytes
+
+/*
+bits 32
+
+; assumes r-x section at 0x100000
+; assumes rw- section at 0x200000
+; assumes r-- section at 0x300000
+; also needs an initialized stack
+
+start:
+   jmp bottom
+top:
+   pop esi
+   and esi, ~0xfff
+   times 30 inc eax
+   mov edi, esi
+   add edi, 0x100000
+   mov ecx, end - start
+   rep movsb
+   and edi, ~0xfff
+   cmp edi, 0x400000
+   jnz next_block
+   hlt
+next_block:
+   jmp edi
+bottom:
+   call top
+end:
+*/
+
+int test_num  = 0;
+uint32_t tests[] = {
+   0x41414141,
+   0x43434343,
+   0x45454545
+};
+
+static int log_num = 1;
+
+#define CODE_SECTION 0x100000
+#define CODE_SIZE 0x1000
+
+// callback for tracing instruction
+static void hook_code(uch handle, uint64_t addr, uint32_t size, void *user_data)
+{
+   uint8_t opcode;
+   if (uc_mem_read(handle, addr, &opcode, 1) != UC_ERR_OK) {
+      printf("not ok %d - uc_mem_read fail during hook_code callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
+   }
+//   printf("ok %d - uc_mem_read for opcode at address 0x%" PRIx64 "\n", log_num++, addr);
+   switch (opcode) {
+      case 0xf4:  //hlt
+         printf("# Handling HLT\n");
+         if (uc_emu_stop(handle) != UC_ERR_OK) {
+            printf("not ok %d - uc_emu_stop fail during hook_code callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
+            _exit(-1);
+         }
+         else {
+            printf("ok %d - hlt encountered, uc_emu_stop called\n", log_num++);
+         }
+         break;
+      default:  //all others
+//         printf("# Handling OTHER\n");
+         break;
+   }
+}
+
+// callback for tracing memory access (READ or WRITE)
+static void hook_mem_write(uch handle, uc_mem_type type,
+        uint64_t addr, int size, int64_t value, void *user_data)
+{
+   printf("# write to memory at 0x%"PRIx64 ", data size = %u, data value = 0x%"PRIx64 "\n", addr, size, value);
+}
+
+// callback for tracing invalid memory access (READ or WRITE)
+static bool hook_mem_invalid(uch handle, uc_mem_type type,
+        uint64_t addr, int size, int64_t value, void *user_data)
+{
+   switch(type) {
+      default:
+         printf("not ok %d - UC_HOOK_MEM_INVALID type: %d at 0x%" PRIx64 "\n", log_num++, type, addr);
+         return false;
+      case UC_MEM_NX:
+         printf("# Fetch from non-executable memory at 0x%"PRIx64 "\n", addr);
+
+         //make page executable
+         if (uc_mem_protect(handle, addr & ~0xfffL, 0x1000, UC_PROT_READ | UC_PROT_EXEC) != UC_ERR_OK) {
+            printf("not ok %d - uc_mem_protect fail for address: 0x%" PRIx64 "\n", log_num++, addr);
+         }
+         else {
+            printf("ok %d - uc_mem_protect success at 0x%" PRIx64 "\n", log_num++, addr);
+         }
+         return true;
+      case UC_MEM_WRITE_NW:
+         printf("# write to non-writeable memory at 0x%"PRIx64 ", data size = %u, data value = 0x%"PRIx64 "\n", addr, size, value);
+
+         if (uc_mem_protect(handle, addr & ~0xfffL, 0x1000, UC_PROT_READ | UC_PROT_WRITE) != UC_ERR_OK) {
+            printf("not ok %d - uc_mem_protect fail during hook_mem_invalid callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
+         }
+         else {
+            printf("ok %d - uc_mem_protect success\n", log_num++);
+         }
+         return true;
+   }
+}
+
+int main(int argc, char **argv, char **envp)
+{
+   uch handle, trace1, trace2;
+   uc_err err;
+   uint32_t esp, eip;
+   int32_t buf1[1024], buf2[1024], readbuf[1024];
+   int i;
+   
+   //don't really care about quality of randomness
+   srand(time(NULL));
+   for (i = 0; i < 1024; i++) {
+      buf1[i] = rand();
+      buf2[i] = rand();
+   }
+
+   printf("# Memory protect test\n");
+
+   // Initialize emulator in X86-32bit mode
+   err = uc_open(UC_ARCH_X86, UC_MODE_32, &handle);
+   if (err) {
+      printf("not ok %d - Failed on uc_open() with error returned: %u\n", log_num++, err);
+      return 1;
+   }
+   else {
+      printf("ok %d - uc_open() success\n", log_num++);
+   }
+
+   uc_mem_map(handle, 0x100000, 0x1000, UC_PROT_READ | UC_PROT_EXEC);
+   uc_mem_map(handle, 0x1ff000, 0x2000, UC_PROT_READ | UC_PROT_WRITE);
+   uc_mem_map(handle, 0x300000, 0x2000, UC_PROT_READ);
+   uc_mem_map(handle, 0xf00000, 0x1000, UC_PROT_READ | UC_PROT_WRITE);
+
+   esp = 0xf00000 + 0x1000;
+
+   // Setup stack pointer
+   if (uc_reg_write(handle, UC_X86_REG_ESP, &esp)) {
+      printf("not ok %d - Failed to set esp. quit!\n", log_num++);
+      return 2;
+   }
+   else {
+      printf("ok %d - ESP set\n", log_num++);
+   }
+
+   // fill in sections that shouldn't get touched
+   if (uc_mem_write(handle, 0x1ff000, (uint8_t*)buf1, 4096)) {
+      printf("not ok %d - Failed to write random buffer 1 to memory, quit!\n", log_num++);
+      return 3;
+   }
+   else {
+      printf("ok %d - Random buffer 1 written to memory\n", log_num++);
+   }
+
+   if (uc_mem_write(handle, 0x301000, (uint8_t*)buf2, 4096)) {
+      printf("not ok %d - Failed to write random buffer 2 to memory, quit!\n", log_num++);
+      return 4;
+   }
+   else {
+      printf("ok %d - Random buffer 2 written to memory\n", log_num++);
+   }
+
+   // write machine code to be emulated to memory
+   if (uc_mem_write(handle, 0x100000, PROGRAM, sizeof(PROGRAM))) {
+      printf("not ok %d - Failed to write emulation code to memory, quit!\n", log_num++);
+      return 5;
+   }
+   else {
+      printf("ok %d - Program written to memory\n", log_num++);
+   }
+
+   if (uc_hook_add(handle, &trace2, UC_HOOK_CODE, hook_code, NULL, 1, 0) != UC_ERR_OK) {
+      printf("not ok %d - Failed to install UC_HOOK_CODE handler\n", log_num++);
+      return 6;
+   }
+   else {
+      printf("ok %d - UC_HOOK_CODE installed\n", log_num++);
+   }
+
+   // intercept memory write events
+   if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_WRITE, hook_mem_write, NULL) != UC_ERR_OK) {
+      printf("not ok %d - Failed to install UC_HOOK_MEM_WRITE handler\n", log_num++);
+      return 7;
+   }
+   else {
+      printf("ok %d - UC_HOOK_MEM_WRITE installed\n", log_num++);
+   }
+
+   // intercept invalid memory events
+   if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_INVALID, hook_mem_invalid, NULL) != UC_ERR_OK) {
+      printf("not ok %d - Failed to install UC_HOOK_MEM_INVALID handler\n", log_num++);
+      return 8;
+   }
+   else {
+      printf("ok %d - UC_HOOK_MEM_INVALID installed\n", log_num++);
+   }
+
+   // emulate machine code until told to stop by hook_code
+   printf("# BEGIN execution\n");
+   err = uc_emu_start(handle, 0x100000, 0x400000, 0, 0);
+   if (err != UC_ERR_OK) {
+      printf("not ok %d - Failure on uc_emu_start() with error %u:%s\n", log_num++, err, uc_strerror(err));
+      return 9;
+   }
+   else {
+      printf("ok %d - uc_emu_start complete\n", log_num++);
+   }
+   printf("# END execution\n");
+
+   // get ending EIP
+   if (uc_reg_read(handle, UC_X86_REG_EIP, &eip)) {
+      printf("not ok %d - Failed to read eip.\n", log_num++);
+   }
+   else {
+      printf("ok %d - Ending EIP 0x%x\n", log_num++, eip);
+   }
+
+   //make sure that random blocks didn't get nuked
+   // fill in sections that shouldn't get touched
+   if (uc_mem_read(handle, 0x1ff000, (uint8_t*)readbuf, 4096)) {
+      printf("not ok %d - Failed to read random buffer 1 from memory\n", log_num++);
+   }
+   else {
+      printf("ok %d - Random buffer 1 read from memory\n", log_num++);
+      if (memcmp(buf1, readbuf, 4096)) {
+         printf("not ok %d - Random buffer 1 contents are incorrect\n", log_num++);
+      }
+      else {
+         printf("ok %d - Random buffer 1 contents are correct\n", log_num++);
+      }
+   }
+
+   if (uc_mem_read(handle, 0x301000, (uint8_t*)readbuf, 4096)) {
+      printf("not ok %d - Failed to read random buffer 2 from memory\n", log_num++);
+   }
+   else {
+      printf("ok %d - Random buffer 2 read from memory\n", log_num++);
+      if (memcmp(buf2, readbuf, 4096)) {
+         printf("not ok %d - Random buffer 2 contents are incorrect\n", log_num++);
+      }
+      else {
+         printf("ok %d - Random buffer 2 contents are correct\n", log_num++);
+      }
+   }
+
+   if (uc_close(&handle) == UC_ERR_OK) {
+      printf("ok %d - uc_close complete\n", log_num++);
+   }
+   else {
+      printf("not ok %d - uc_close complete\n", log_num++);
+   }
+
+   return 0;
+}
diff --git a/samples/mem_protect.c b/samples/mem_protect.c
index 4afb88c1..025f9953 100644
--- a/samples/mem_protect.c
+++ b/samples/mem_protect.c
@@ -117,7 +117,7 @@ static void hook_code(uch handle, uint64_t addr, uint32_t size, void *user_data)
          printf("# Handling HLT\n");
          if (uc_emu_stop(handle) != UC_ERR_OK) {
             printf("not ok %d - uc_emu_stop fail during hook_code callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
-            _exit(1);
+            _exit(-1);
          }
          else {
             printf("ok %d - hlt encountered, uc_emu_stop called\n", log_num++);
@@ -155,7 +155,7 @@ static bool hook_mem_invalid(uch handle, uc_mem_type type,
             printf("ok %d - uc_mem_read success after mem_protect at test %d\n", log_num++, test_num - 1);
          }
 
-         if (uc_mem_protect(handle, addr & ~0xfff, 0x1000, UC_PROT_READ | UC_PROT_WRITE) != UC_ERR_OK) {
+         if (uc_mem_protect(handle, addr & ~0xfffL, 0x1000, UC_PROT_READ | UC_PROT_WRITE) != UC_ERR_OK) {
             printf("not ok %d - uc_mem_protect fail during hook_mem_invalid callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
          }
          else {
@@ -208,7 +208,7 @@ int main(int argc, char **argv, char **envp)
 
    if (uc_mem_write(handle, 0x401000, (uint8_t*)buf2, 4096)) {
       printf("not ok %d - Failed to write random buffer 2 to memory, quit!\n", log_num++);
-      return 2;
+      return 3;
    }
    else {
       printf("ok %d - Random buffer 2 written to memory\n", log_num++);
@@ -217,7 +217,7 @@ int main(int argc, char **argv, char **envp)
    // write machine code to be emulated to memory
    if (uc_mem_write(handle, CODE_SECTION, PROGRAM, sizeof(PROGRAM))) {
       printf("not ok %d - Failed to write emulation code to memory, quit!\n", log_num++);
-      return 2;
+      return 4;
    }
    else {
       printf("ok %d - Program written to memory\n", log_num++);
@@ -225,7 +225,7 @@ int main(int argc, char **argv, char **envp)
 
    if (uc_hook_add(handle, &trace2, UC_HOOK_CODE, hook_code, NULL, 1, 0) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_CODE handler\n", log_num++);
-      return 3;
+      return 5;
    }
    else {
       printf("ok %d - UC_HOOK_CODE installed\n", log_num++);
@@ -234,7 +234,7 @@ int main(int argc, char **argv, char **envp)
    // intercept memory write events
    if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_WRITE, hook_mem_write, NULL) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_MEM_WRITE handler\n", log_num++);
-      return 4;
+      return 6;
    }
    else {
       printf("ok %d - UC_HOOK_MEM_WRITE installed\n", log_num++);
@@ -243,7 +243,7 @@ int main(int argc, char **argv, char **envp)
    // intercept invalid memory events
    if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_INVALID, hook_mem_invalid, NULL) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_MEM_INVALID handler\n", log_num++);
-      return 4;
+      return 7;
    }
    else {
       printf("ok %d - UC_HOOK_MEM_INVALID installed\n", log_num++);
@@ -251,10 +251,10 @@ int main(int argc, char **argv, char **envp)
 
    // emulate machine code until told to stop by hook_code
    printf("# BEGIN execution\n");
-   err = uc_emu_start(handle, CODE_SECTION, CODE_SECTION + CODE_SIZE, 0, 100);
+   err = uc_emu_start(handle, CODE_SECTION, CODE_SECTION + CODE_SIZE, 0, 0);
    if (err != UC_ERR_OK) {
       printf("not ok %d - Failure on uc_emu_start() with error %u:%s\n", log_num++, err, uc_strerror(err));
-      return 5;
+      return 8;
    }
    else {
       printf("ok %d - uc_emu_start complete\n", log_num++);
diff --git a/samples/mem_unmap.c b/samples/mem_unmap.c
index 60f3039a..6f93673d 100644
--- a/samples/mem_unmap.c
+++ b/samples/mem_unmap.c
@@ -111,7 +111,7 @@ static void hook_code(uch handle, uint64_t addr, uint32_t size, void *user_data)
          printf("# Handling HLT\n");
          if (uc_emu_stop(handle) != UC_ERR_OK) {
             printf("not ok %d - uc_emu_stop fail during hook_code callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
-            _exit(1);
+            _exit(-1);
          }
          else {
             printf("ok %d - hlt encountered, uc_emu_stop called\n", log_num++);
@@ -149,7 +149,7 @@ static bool hook_mem_invalid(uch handle, uc_mem_type type,
             printf("not ok %d - uc_mem_read success after unmap at test %d\n", log_num++, test_num - 1);
          }
 
-         if (uc_mem_map(handle, addr & ~0xfff, 0x1000, UC_PROT_READ | UC_PROT_WRITE) != UC_ERR_OK) {
+         if (uc_mem_map(handle, addr & ~0xfffL, 0x1000, UC_PROT_READ | UC_PROT_WRITE) != UC_ERR_OK) {
             printf("not ok %d - uc_mem_map fail during hook_mem_invalid callback, addr: 0x%" PRIx64 "\n", log_num++, addr);
          }
          else {
@@ -202,7 +202,7 @@ int main(int argc, char **argv, char **envp)
 
    if (uc_mem_write(handle, 0x401000, (uint8_t*)buf2, 4096)) {
       printf("not ok %d - Failed to write random buffer 2 to memory, quit!\n", log_num++);
-      return 2;
+      return 3;
    }
    else {
       printf("ok %d - Random buffer 2 written to memory\n", log_num++);
@@ -211,7 +211,7 @@ int main(int argc, char **argv, char **envp)
    // write machine code to be emulated to memory
    if (uc_mem_write(handle, CODE_SECTION, PROGRAM, sizeof(PROGRAM))) {
       printf("not ok %d - Failed to write emulation code to memory, quit!\n", log_num++);
-      return 2;
+      return 4;
    }
    else {
       printf("ok %d - Program written to memory\n", log_num++);
@@ -219,7 +219,7 @@ int main(int argc, char **argv, char **envp)
 
    if (uc_hook_add(handle, &trace2, UC_HOOK_CODE, hook_code, NULL, 1, 0) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_CODE handler\n", log_num++);
-      return 3;
+      return 5;
    }
    else {
       printf("ok %d - UC_HOOK_CODE installed\n", log_num++);
@@ -228,7 +228,7 @@ int main(int argc, char **argv, char **envp)
    // intercept memory write events
    if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_WRITE, hook_mem_write, NULL) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_MEM_WRITE handler\n", log_num++);
-      return 4;
+      return 6;
    }
    else {
       printf("ok %d - UC_HOOK_MEM_WRITE installed\n", log_num++);
@@ -237,7 +237,7 @@ int main(int argc, char **argv, char **envp)
    // intercept invalid memory events
    if (uc_hook_add(handle, &trace1, UC_HOOK_MEM_INVALID, hook_mem_invalid, NULL) != UC_ERR_OK) {
       printf("not ok %d - Failed to install UC_HOOK_MEM_INVALID handler\n", log_num++);
-      return 4;
+      return 7;
    }
    else {
       printf("ok %d - UC_HOOK_MEM_INVALID installed\n", log_num++);
@@ -245,10 +245,10 @@ int main(int argc, char **argv, char **envp)
 
    // emulate machine code until told to stop by hook_code
    printf("# BEGIN execution\n");
-   err = uc_emu_start(handle, CODE_SECTION, CODE_SECTION + CODE_SIZE, 0, 100);
+   err = uc_emu_start(handle, CODE_SECTION, CODE_SECTION + CODE_SIZE, 0, 0);
    if (err != UC_ERR_OK) {
       printf("not ok %d - Failure on uc_emu_start() with error %u:%s\n", log_num++, err, uc_strerror(err));
-      return 5;
+      return 8;
    }
    else {
       printf("ok %d - uc_emu_start complete\n", log_num++);