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List:       linux-man
Subject:    Re: execve(2) man page: "absolute pathname" inconsistency
From:       "Alejandro Colomar (man-pages)" <alx.manpages () gmail ! com>
Date:       2021-07-03 18:56:02
Message-ID: 9558b097-7760-beb5-be4d-13e298461e82 () gmail ! com
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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/


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