arch/sim: Add MM_FILL_ALLOCATIONS support to sim customized heap.

[yushuailong]

Summary

When CONFIG_MM_UMM_CUSTOMIZE_MANAGER is enabled, the sim heap bypasses mm_heap/tlsf entirely and calls host malloc/free directly, so MM_FILL_ALLOCATIONS has no effect. Add fill pattern support directly in sim_ummheap.c:

• malloc: fill user region with 0xaa
• free: fill user region with 0x55
• realloc: fill extended region with 0xaa

This helps detect uninitialized reads in sim environment, which ASan does not support.

Impact

Only affects sim arch when both CONFIG_MM_UMM_CUSTOMIZE_MANAGER and CONFIG_MM_FILL_ALLOCATIONS are enabled.

Testing

Host: Linux x86_64 (Ubuntu)
Board: sim (simulator)
Config: sim:ostest with CONFIG_MM_UMM_CUSTOMIZE_MANAGER=y and CONFIG_MM_FILL_ALLOCATIONS=y
Toolchain: GCC

Test case :

  #define TEST_SIZE       64
  #define REALLOC_SIZE    128
  #define MAGIC_ALLOC     0xaa
  #define MAGIC_FREE      0x55

  /* Test 1: malloc fills user region with 0xaa */
  static void test_malloc_fill(void)
  {
    unsigned char *p = malloc(TEST_SIZE);
    assert(check_pattern(p, MAGIC_ALLOC, TEST_SIZE) == 0);
    free(p);
  }

  /* Test 2: free fills user region with 0x55 */
  static void test_free_fill(void)
  {
    unsigned char *p = malloc(TEST_SIZE);
    unsigned char *saved = p;
    memset(p, 0x12, TEST_SIZE);
    free(p);
    assert(check_pattern(saved, MAGIC_FREE, TEST_SIZE) == 0);
  }

  /* Test 3: realloc extend fills grown region with 0xaa */
  static void test_realloc_extend_fill(void)
  {
    unsigned char *p = malloc(TEST_SIZE);
    memset(p, 0x12, TEST_SIZE);
    p = realloc(p, REALLOC_SIZE);
    assert(check_pattern(p, 0x12, TEST_SIZE) == 0);          /* old data preserved */
    assert(check_pattern(p + TEST_SIZE, MAGIC_ALLOC,
                         REALLOC_SIZE - TEST_SIZE) == 0);     /* extended region filled */
    free(p);
  }

  /* Test 4: realloc shrink preserves data */
  static void test_realloc_shrink_no_corrupt(void)
  {
    unsigned char *p = malloc(REALLOC_SIZE);
    memset(p, 0x34, REALLOC_SIZE);
    p = realloc(p, TEST_SIZE);
    assert(check_pattern(p, 0x34, TEST_SIZE) == 0);
    free(p);
  }

int main(int argc, FAR char *argv[])
{
  printf("\n=== MM_FILL_ALLOCATIONS Test ===\n\n");

  test_malloc_fill();
  test_free_fill();
  test_realloc_extend_fill();
  test_realloc_shrink_no_corrupt();

  printf("\n=== Test Complete ===\n");
  return 0;
}

Test log:

=== MM_FILL_ALLOCATIONS Test ===

TEST: malloc fill 0xaa ... PASS
TEST: free fill 0x55 ... PASS
TEST: realloc extend fill 0xaa ... PASS
TEST: realloc shrink preserves data ... PASS

=== Test Complete ===

All 4 tests pass.