id = 1687
title = "Memory leak for x86 guest on macOS ARM host"
state = "opened"
created_at = "2023-06-05T19:27:51.499Z"
closed_at = "n/a"
labels = []
url = "https://gitlab.com/qemu-project/qemu/-/issues/1687"
host-os = "macOS Darwin"
host-arch = "ARM"
qemu-version = "n/a"
guest-os = "Ubuntu 22.04"
guest-arch = "x86"
description = """QEMU is used by docker to run `x86` binaries on Apple silicon. Then using `mmap` followed by `munmap` results in a memory leak manifested by continuously growing RSS memory usage when running `mmap` and `munmap` in a loop, e.g., when running the following binary:

```
#include <stdio.h>
#include <unistd.h>
#include <sys/mman.h>

const int page = 4096;

int work(int N) {
  int *ptr = mmap(NULL, N * sizeof(int), PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);

  if (ptr == MAP_FAILED) {
    printf("Mapping Failed\\n");
    return 1;
  }

  for(int i = 0; i < N; i++) {
    ptr[i] = i * 10;
  }

  int err = munmap(ptr, N * sizeof(int));
  if (err != 0) {
    printf("UnMapping Failed\\n");
    return 1;
  }

  return 0;
}

int main() {
  int N = page * 1024;

  while (1) {
    int res = work(N);
    if (res) {
      return res;
    }
    printf(".\\n");
  }

  return 0;
}
```"""
reproduce = """```
$ LEAK=$(docker run --platform linux/amd64 -d -it martin2718/mmap-leak ./a.out)
$ docker exec -it $LEAK top        # you should observe that RES for a.out keeps growing
$ docker exec -it $LEAK pmap -x 1  # you should see a single memory mapping whose RSS memory usage keeps growing
$ docker kill $LEAK                # abort the experiment
```"""
additional = "n/a"