Reading mmap() values....

[nightpoison]

So i've mapped a section of code utilizing the mmap() call.

size_t pSize = getpagesize();
printf("Page Size: %zu\n", pSize);
int dh = open("/dev/mem", O_RDWR | O_SYNC); // Open /dev/mem which represents the whole physical memory

unsignedint *addr = mmap(NULL, pSize, PROT_READ, MAP_SHARED, dh, 0x4000000);  // Memory map source address

Now I have two different functions that are reading the memory at what I believe to be the same address.

voidcapture(void *addr, intbyteCnt)
{
  unsigned int *p = addr;
  int offset;
  for (offset = 0; offset < byteCnt; offset++) {
    printf("%02X", p[offset]);
    if (offset % 4 == 3) {
      printf(" ");
    }
  }
  printf("\n");

}

and

voidmemCapture(void *addr, intbyteCnt)
{

  unsigned int a;
  char *p = addr;
  memcpy(&a, p, byteCnt);
  printf("%X\n", a);

}

Why am i seeing two different values when I run both functions back to back.

If I attempt to capture four bytes from both I get values such as
587eb357
57b3e758

[Salem]

So what are your actual results?

[nightpoison]

So what are your actual results?

sorry about that. I've updated the OP, but here are the values that I'm seeing
587eb357
57b3e758

[Salem]

Well one looks like the big-endian version of the other.

Or if you want to see bytes in the order of significance in a little endian integer, you need to print them backwards.
So that the MSB is on the left.

for (offset = byteCnt-1; offset >= 0; offset--)

[nightpoison]

Well one looks like the big-endian version of the other.

Or if you want to see bytes in the order of significance in a little endian integer, you need to print them backwards.
So that the MSB is on the left.

for (offset = byteCnt-1; offset >= 0; offset--)

I kept looking and looking and I didn't notice that. its 99% the same

except for one part.

587eb357
57b3e758

the 7e e7 appears to be flipped. you have everthing else matching

58 7e b3 57

57 b3 e7 58

I don't work with memory at this level, so this is fairly new to me.

[Salem]

Well the other problem is you're stepping through memory an int at a time here
unsigned int *p = addr;

Before you go poking around, make sure the basics work.

#include <stdio.h>
#include <string.h>

void capture(void *addr, int byteCnt)
{
  unsigned char *p = addr;
  int offset;
  for (offset = byteCnt-1; offset >= 0; offset--) {
    printf("%02X", p[offset]);
    if (offset % 4 == 3) {
      printf(" ");
    }
  }
  printf("\n");
}

void memCapture(void *addr, int byteCnt)
{
  unsigned int a;
  char *p = addr;
  memcpy(&a, p, byteCnt);
  printf("%X\n", a);
}

int main() {
  char test[] = "hello world";
  capture(&test[5],4);
  memCapture(&test[5],4);
}