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

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Message-Id: <20230703112404.496996-1-falcon@tinylab.org>
Date:   Mon,  3 Jul 2023 19:24:04 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     w@....eu
Cc:     arnd@...db.de, david.laight@...lab.com, falcon@...ylab.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux@...ssschuh.net,
        thomas@...ch.de
Subject: Re: [PATCH v5 14/14] selftests/nolibc: add mmap and munmap test cases

> On Mon, Jul 03, 2023 at 04:06:47PM +0800, Zhangjin Wu wrote:
> > > >     /* 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
> > > 
> > > No, please, not like this. Just copy argv[0] (the pointer not the
> > > contents) and you're fine:
> > >
> > >     static const char *argv0;
> > > 
> > >     int main(int argc, char **argv, char **envp)
> > >     {
> > >             argv0 = argv[0];
> > >             ...
> > >     }
> > > 
> > > Nothing more, nothing less. Your program will always have its correct
> > > path when being called unless someone purposely forces it to something
> > > different, which is not our concern at all since this is a test program.
> > > And I'd rather call it "argv0" which exactly tells us what it contains
> > > than "exe" which can be misleading for that precise reason.
> > >
> > 
> > Yeah, locally, I just used a global argv0 pointer directly, but
> > chroot_exe("./nolibc-test") not work when run 'libc-test' in host
> > system, that is why I tried to get an absolute path ;-)
> > 
> >     CASE_TEST(chroot_exe);        EXPECT_SYSER(1, chroot(exe), -1, ENOTDIR); break;
> > 
> >     -->
> > 
> >     19 chroot_exe = -1 ENOENT  != (-1 ENOTDIR)                      [FAIL]
> 
> Then we have a problem somewhere else and the test should be debugger
> instead. Are you sure there isn't a successful chdir() test before it
> for example, that would change the directory ? If so maybe we just need
> to save the current dir before calling it and restore it later.
>

Yes, as Thomas pointed out, the chdir test cases changed current
directory to "/" just before chroot_exe(), so, restore it with
chdir(getenv("PWD")) solves the issue.

> > I removed the "proc ?" check manually to test if it also work with
> > CONFIG_PROC_FS=n. it doesn't work, without absolute path, we need to add
> > the ENOENT errno back to the errno check list.
> 
> Same as above.
> 
> > I'm not sure if the other syscalls require an absolute path, so, the
> > realpath() is called in this proposed method.
> 
> No, please do not overengineer tests. That's only hiding the dust under
> the carpet and people adding more tests later that will randomly fail
> will have a very hard time trying to figure what's happening under the
> hood. If a test doesn't work as expected, we must not try to work around
> it, but arrange to fix it.

That's right, thanks.

Best regards,
Zhangjin

> 
> Thanks,
> Willy