Re: [PATCH v5 14/14] selftests/nolibc: add mmap and munmap test cases

[Zhangjin Wu]

> Hi Zhangjin,
> 
> On Wed, Jun 28, 2023 at 09:51:57PM +0800, Zhangjin Wu wrote:
> > Three mmap/munmap related test cases are added:
> > 
> > - mmap_bad: the length argument must be greater than 0, otherwise, fail
> >   with -EINVAL.
> > 
> > - munmap_bad: invalid (void *)-1 address fail with -EINVAL.
> > 
> > - mmap_munmap_good: mmap() a file with good offset and then munmap().
> > 
> > Note, it is not easy to find a unique file for mmap() in different
> > scenes, so, a file list is used to search the right one:
> > 
> > - /proc/1/exe, for 'run' and 'run-user' target
> >   'run-user' can not find '/proc/self/exe'
> > 
> > - /proc/self/exe, for 'libc-test' target
> >   normal program 'libc-test' has no permission to access '/proc/1/exe'
> 
> Strictly speaking, if your executable is not readable (e.g. chmod 111
> due to a restrictive umask) it will also fail that one.
>

ok.

> > - the others, for kernel without procfs
> >   let it pass even with 'worst case' kernel configs
> 
> You should include /dev/zero, which is commonly used to allocate anonymous
> memory and is more likely present and readable than any of the other files.
> And another file of choice is obviously argv[0] ;-)  In this case you don't
> need any of the other extra ones. Thus I could suggest that you try in this
> order:
> 
>     /dev/zero, /proc/self/exe, /proc/1/exe, argv[0]
> 
> and be done with it. That doesn't prevent one from extending the list if
> really needed later, but I doubt it would be needed. Also, it's already
> arranged in a read-write, then read-only fallbacks mode, so if we later
> need to add more complex tests involving writes, the writable /dev/zero
> will have precedence.
>

Cool, both /dev/zero and argv[0] are very good candidates ;-)

Just verified both of them, works perfectly.

- /dev/zero

  we need to mknod it in prepare() and also, in test_mmap_munmap(),
  stat() return a zero size of /dev/zero, in this case, we should assign
  a non-zero file_size ourselves.

    -       file_size = stat_buf.st_size;
    +       /* file size of the special /dev/zero is 0, let's assign one manually */
    +       if (i == 0)
    +               file_size = 3*page_size - 1;
    +       else
    +               file_size = stat_buf.st_size;


- argv[0]

  since nolibc has no realpath() currently, we can simply
  support the current path and the absolute path like this:

    nolibc-test.c:

    /* assigned as argv[0] in main(), will be used by some tests */
    static char exe[PATH_MAX + 1];

    main():

    /* get absolute path of myself, nolibc has no realpath() currently */
    #ifndef NOLIBC
            realpath(argv[0], exe);
    #else
            /* assume absolute path has no "./" */
            if (strncmp(argv[0], "./", 2) != 0)
                    strncat(exe, argv[0], strlen(argv[0]) + 1);
            else {
                    pwd = getenv("PWD");
                    /* skip the ending '\0' */
                    strncat(exe, getenv("PWD"), strlen(pwd));
                    /* skip the first '.' */
                    strncat(exe, argv[0] + 1, strlen(argv[0]));
            }
    #endif

A full functional realpath() is a little complex, such as '../' support and
even symlink support, let's delay its requirement at current stage ;-)

one or both of them may also help the other test cases:

- chroot_exe (used '/init' before)

    CASE_TEST(chroot_exe);        EXPECT_SYSER(1, chroot(proc ? "/proc/self/exe" : exe), -1, ENOTDIR); break;

- chmod_exe (replace the one: chmod_tmpdir in another patchset)

    CASE_TEST(chmod_exe);       EXPECT_SYSZR(1, chmod(proc ? "/proc/self/exe" : exe, 0555)); break;

    It should be safe enough to only remove the writable attribute for the test
    program.

- stat_timestamps (used '/init' before)

    if (stat("/proc/self/", &st) && stat(exe, &st) && stat("/dev/zero", &st) && stat("/", &st))

Will update the related patches with them.

Thanks,
Zhangjin

> Willy