Re: [Bug 216876] New: prototype for execveat() in the documentation appears wrong

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi,

On 1/2/23 04:47, bugzilla-daemon@kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=216876
> 
>              Bug ID: 216876
>             Summary: prototype for execveat() in the documentation appears
>                      wrong
>             Product: Documentation
>             Version: unspecified
>            Hardware: All
>                  OS: Linux
>              Status: NEW
>            Severity: low
>            Priority: P1
>           Component: man-pages
>            Assignee: documentation_man-pages@kernel-bugs.osdl.org
>            Reporter: markgaleck@gmail.com
>          Regression: No
> 
> prototype for execveat() in the documentation is:
> 
> int execveat(int dirfd, const char *pathname,
>                      const char *const argv[], const char *const envp[],
>                      int flags);
> 
> 
> This appears to be inconsistent with similar functions, other documentation,
> and my sources (latest Ubuntu distribution).
> 
> 
> I think two of the "const" should be dropped so that we should have:
> 
> int execveat(int dirfd, const char *pathname,
>                      char *const argv[], char *const envp[],
>                      int flags);

Thanks for the report!

This was introduced in commit 71a25d4c79b1ccf538f6b813c834bbc4197f6370
"execveat.2: Fix prototype".

The reason is that the kernel uses the const:

alx@asus5775:~/src/linux/linux$ grepc execveat
./include/linux/compat.h:851:
asmlinkage long compat_sys_execveat(int dfd, const char __user *filename,
		     const compat_uptr_t __user *argv,
		     const compat_uptr_t __user *envp, int flags);


./include/linux/syscalls.h:1011:
asmlinkage long sys_execveat(int dfd, const char __user *filename,
			const char __user *const __user *argv,
			const char __user *const __user *envp, int flags);


./fs/exec.c:2096:
SYSCALL_DEFINE5(execveat,
		int, fd, const char __user *, filename,
		const char __user *const __user *, argv,
		const char __user *const __user *, envp,
		int, flags)
{
	return do_execveat(fd,
			   getname_uflags(filename, flags),
			   argv, envp, flags);
}


./fs/exec.c:2115:
COMPAT_SYSCALL_DEFINE5(execveat, int, fd,
		       const char __user *, filename,
		       const compat_uptr_t __user *, argv,
		       const compat_uptr_t __user *, envp,
		       int,  flags)
{
	return compat_do_execveat(fd,
				  getname_uflags(filename, flags),
				  argv, envp, flags);
}


It seems that glibc added a wrapper recently, and I didn't check that the 
prototype changed:

alx@asus5775:~/src/gnu/glibc$ grepc execveat
./posix/unistd.h:300:
extern int execveat (int __fd, const char *__path, char *const __argv[],
                      char *const __envp[], int __flags)
     __THROW __nonnull ((2, 3));


./sysdeps/unix/sysv/linux/execveat.c:25:
int
execveat (int dirfd, const char *path, char *const argv[], char *const envp[],
           int flags)
{
   /* Avoid implicit array coercion in syscall macros.  */
   return INLINE_SYSCALL_CALL (execveat, dirfd, path, &argv[0], &envp[0],
			      flags);
}


I CCd glibc so that they can comment.

Cheers,

Alex

P.S.:  There's some problem in bugzilla that it's not receiving my replies, so I 
CCed everyone involved so we can keep the discussion in the mailing list.

P.S.2:  Ping, Konstantin, please check that.

-- 
<http://www.alejandro-colomar.es/>

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