# How to display physical memory

in OS kernel code, a physical address is uint64, but it is often being cast as a void*, or char*, then carry around. I think this makes a lot of interface like memset, memcpy, etc more convenient to use.

```c
void vmprint_helper(pagetable_t *pagetable*, char* prefix, int level) {
  // there are 2^9 = 512 PTEs in a page table.
  for(int k = 0; k < 512; k++) {
    pte_t pte = pagetable[k];
    if(pte & PTE_V) {
      printf(“%s%d: pte %p pa %p\n”, prefix, k, pte, PTE2PA(pte));
      int next_level = level - 1;
      if (level > 0) {
        uint64 child = PTE2PA(pte);
        pagetable_t pt = (pagetable_t)child;
        vmprint_helper(pt, print_prefix(next_level), next_level);
      }
    }
  }
}

void vmprint(pagetable_t *pagetable*)
{
  printf(“page table %p\n”, pagetable);
  vmprint_helper(pagetable, “..”, 2);
}
```

```
page table 0x0000000087f6e000
..0: pte 0x0000000021fda801 pa 0x0000000087f6a000
....0: pte 0x0000000021fda401 pa 0x0000000087f69000
......0: pte 0x0000000021fdac1f pa 0x0000000087f6b000
......1: pte 0x0000000021fda00f pa 0x0000000087f68000
......2: pte 0x0000000021fd9c1f pa 0x0000000087f67000
..255: pte 0x0000000021fdb401 pa 0x0000000087f6d000
....511: pte 0x0000000021fdb001 pa 0x0000000087f6c000
......510: pte 0x0000000021fdd807 pa 0x0000000087f76000
......511: pte 0x000000002000200b pa 0x0000000080008000
init: starting sh
page table 0x0000000087f63000
..0: pte 0x0000000021fd7c01 pa 0x0000000087f5f000
....0: pte 0x0000000021fd7801 pa 0x0000000087f5e000
......0: pte 0x0000000021fd801f pa 0x0000000087f60000
......1: pte 0x0000000021fd741f pa 0x0000000087f5d000
......2: pte 0x0000000021fd700f pa 0x0000000087f5c000
......3: pte 0x0000000021fd6c1f pa 0x0000000087f5b000
..255: pte 0x0000000021fd8801 pa 0x0000000087f62000
....511: pte 0x0000000021fd8401 pa 0x0000000087f61000
......510: pte 0x0000000021fdbc07 pa 0x0000000087f6f000
......511: pte 0x000000002000200b pa 0x0000000080008000
```

Another reason cast uint64 to void\* is easy to print. (see above code about how to print page tables)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://xiayingp.gitbook.io/build_a_os/virtual-memory/untitled-1/how-to-display-physical-memory.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.