Re: $ORIGIN

[Alan Barrett <apb%cequrux.com@localhost>]

On Sun, 26 Jan 2014, matthew green wrote:
> > Aren't the majority of exec's done with a pathname?  Why not 
> > cache that name if the image has DF_ORIGIN set?
>
> why do you think this?
>
> i almost never call something via a pathname, and besides maybe 
> build.sh, most builds call "gcc" etc directly.

If the user or any parent program runs a child program using 
an unqualified name, then the PATH will be searched to resolve 
the unqualified program name to a full pathname.  This usually 
happens in the users's shell, or in libc's exec*p* functions, or 
in similar features in other languages, and it happens before the 
request reaches the kernel's execve(2) syscall.

Exceptions are when the program is explicitly called using a 
relative path (e.g. "./foo"), or when the PATH contains "." or 
similar relative components, or when fexecve(2) is used instead of 
execve(2).

I don't have measurements, but I expect that full pathnames will 
be available to the kernel in the majority of cases, even if users 
or calling programs specify full pathnames in a minority of cases.

--apb (Alan Barrett)