Re: execve(2) man page: "absolute pathname" inconsistency

["Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>]

Hi Nora,

On 6/24/21 10:42 PM, Nora Platiel wrote:
> Hello,
> I'm reporting a problem with the execve(2) man page (see the "absolute pathname" part):
> 
>> If the pathname argument of execve() specifies an interpreter
>> script, then interpreter will be invoked with the following
>> arguments:
>>
>>     interpreter [optional-arg] pathname arg...
>>
>> where pathname is the absolute pathname of the file specified as
>>                       ^^^^^^^^^^^^^^^^^
>> the first argument of execve(), and arg...  is the series of
>> words pointed to by the argv argument of execve(), starting at
>> argv[1].  Note that there is no way to get the argv[0] that was
>> passed to the execve() call.
> 
> Then in the final example:
> 
>> $ ./execve ./script
>> argv[0]: ./myecho
>> argv[1]: script-arg
>> argv[2]: ./script
>> argv[3]: hello
>> argv[4]: world
> 
> According to the description, argv[2] is supposed to be the *absolute pathname* of "./script" but it is not.
> (In path_resolution(7), an absolute pathname is defined to be a pathname starting with a '/' character.)
> 
> I tested the example with kernel 4.4.246 and the output is the same as the one in the man page (relative paths are preserved).
> I don't know about newer kernels, but if I understand correctly, either the "absolute pathname" wording is incorrect or the example is.
> (In the latter case, perhaps the man page could also mention the change in behavior.)
> 
> The "absolute pathname" wording was introduced here:
> https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=60f16bf2fe6bd2d2d001d0a41936e778b1e7e3f6
> https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=63059c4b527d0da73666da5ff29dcc902e219371

Thanks for all of the info and links.

I think you're right.  In fact, POSIX talks about pathname, and not
absolute pathname
(<https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html>).

However, the kernel documentation talks about 'full path', so I'm not
sure if maybe some versions of the kernel did not support relative paths
 (<https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html>).

I added Shawn to the thread, so maybe he can shed some light (he added
that text).

Regards,

Alex


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/