Re: Change the executing of a 0-byte file to be an error...

From: Harti Brandt (hartmut.brandt_at_dlr.de)
Date: 06/10/05

  • Next message: Dag-Erling Smørgrav: "Re: Bug in #! processing - "pear broken on current"" 
    Date: Fri, 10 Jun 2005 14:00:06 +0200 (CEST)
To: Garance A Drosihn <drosih@rpi.edu>

    On Fri, 10 Jun 2005, Garance A Drosihn wrote:

    GAD>At 12:11 PM +0100 6/10/05, Ceri Davies wrote:
    GAD>> On Fri, Jun 10, 2005, Garance A Drosihn wrote:
    GAD>> >
    GAD>> > If a file is empty and executable, that empty file can be
    GAD>> > executed without generating any error.
    GAD>>
    GAD>> Are you sure? It seems to be a function of the shell more than
    GAD>> anything; the transcript below does exactly the same on both
    GAD>> FreeBSD 4-STABLE and Solaris 8:
    GAD>>
    GAD>> $ sh
    GAD>> $ PS1='sh$ '
    GAD>> sh$ touch empty ; chmod +x empty
    GAD>> sh$ ./empty
    GAD>> sh$ echo $?
    GAD>> 0
    GAD>> sh$ PS1='zsh$ ' zsh
    GAD>> zsh$ zsh
    GAD>> zsh$ ./empty
    GAD>> zsh: exec format error: ./empty
    GAD>> zsh$
    GAD>
    GAD>Well, zsh can certainly add whatever processing it likes, but my main
    GAD>interest is what routines like 'exec()' will do with the file. In
    GAD>particular, I'm concerned with what happens when either `make' or `sh'
    GAD>execute some 0-byte file, because those are commands which will be
    GAD>doing the most command-executing in the process of `make buildworld'.
    GAD>
    GAD>I'll admit I did not notice that zsh made that check, as I only checked
    GAD>with `sh', `bash', and (inadvertently) `make'. It might be that the
    GAD>kernel is already doing the right thing, and what I actually need to
    GAD>change is `sh' and `make' instead of something in the kernel. I'm
    GAD>certainly willing to figure out what needs to be changed, but I
    GAD>thought I should first see if there are any reasons that I should not
    GAD>make such a change in the first place.

    make either uses a shell to execute a command or it uses execl()
    (depending whether you're in -j or -B mode and whether the line contains
    shell metacharacters or builtins), so when execl() does the right thing
    and the shell too, there is nothing to change in make.

    harti
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