initial commit

mem.c

@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <signal.h>
+#include <setjmp.h>
+
+// Global flag and jump buffer for recovery
+static jmp_buf env_buffer;
+static volatile int enable_handler = 0;
+
+void segfault_handler(int signal_num) {
+  if (enable_handler == 1) {
+    longjmp(env_buffer, 1);
+  } else {
+    printf("Segmentation Fault :(");
+    exit(signal_num);
+  }
+}
+int tryDereference(uintptr_t* pointer, uintptr_t* output) {
+  uintptr_t val;
+  if (setjmp(env_buffer) == 0) {
+    enable_handler = 1;
+    *output = *pointer;
+    enable_handler = 0;
+    return 1;
+  }
+  else {
+    enable_handler = 0;
+    return 0;
+  }
+}
+void printMem(uint8_t* location) {
+  if (setjmp(env_buffer) == 0) {
+    enable_handler = 1;
+    printf("%p: 0x%02x\n", location, *location);
+    enable_handler = 0;
+  }
+  else {
+    enable_handler = 0;
+    printf("%p: SEGFAULT\n", location);
+  }
+}
+
+
+uint8_t* flipBit(uint8_t* data, int bit) {
+  return (uint8_t*)((1<<bit) ^ (uintptr_t)data);
+}
+uint32_t nBits() {
+  //NOTE: Just use UINTPTR_MAX
+  uint32_t n = 0;
+  for(uintptr_t p = 1;p > 0; p<<=1) ++n;
+  return n;
+}
+
+int main(int argc, char *argv[])
+{
+  signal(SIGSEGV, segfault_handler);
+  uint32_t nbits = nBits();
+  printf("Using %u bit addresses\n", nbits);
+
+  uint8_t a = 0x55;
+  uint8_t* var = &a;
+  printMem(var-1);
+  printMem(var);
+  printMem(var+1);
+  for (uint32_t i = 0; i < nbits; ++i) {
+    //printf("flipping bit %u\n", i);
+    printMem(flipBit(var, i));
+  }
+
+  return EXIT_SUCCESS;
+}