I have this code below that prints a pointers’ memory address. I’ve never noticed it before, but the returned value is in a specific format that, I guess, does not represent the real virtual memory address.

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

int main()
{
    char* ptr = (char *) malloc(250 * sizeof(char));
    char* ptr2;
    int val;

    strcpy(ptr, "Hello, world!");
    printf("Mem addr: %pn", ptr);
    ...
}

Execution results in:

Mem addr: 0x143e2a0

In kernel context, using printk, you can use the format specifier %p to print this kind of unique identifier that “masks” the real virtual memory address, accordingly to kernel’s documentation. And there is a variation %px that gives you the “real” print of the address.

Is there a way to translate this identifier printed by the user program for a real virtual memory address in a kernel module, for example? I guess I could implement a kernel module to help me getting this real value, because I imagine this kind of information isn’t available in user context for security reasons. Is there a specific kernel routine to do this?

PS1: Notice that, when I say “real virtual memory address” i’m not refering to “physical address”.

PS2: I’m using a linux kernel 6.1 x86_64 to do this.