On Thursday 01 May 2014 21:30:25 Ralf Friedl wrote:
> Tito wrote:
> > while trying to cleanup the debianutils/which command I've spotted
> > a minor glitch in bb's find_execable function as it is not able to handle
> > zero lenght prefixes in the PATH variable:
> >
> > http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html
> > 8.3 Other Environment Variables
> > PATH
> > snip
> > A zero-length prefix is a legacy feature that indicates the current
> > working directory. It appears as two adjacent colons ( "::" ), as an
> > initial colon preceding the rest of the list, or as a trailing colon
> > following the rest of the list. A strictly conforming application shall
> > use an actual pathname (such as .) to represent the current working
> > directory in PATH .
> >
> > The real which command (really a script) in debianutils 4.4 does in fact
> > handle zero-length prefixes in PATH correctly:
> >
> > for ELEMENT in $PATH; do
> > if [ -z "$ELEMENT" ]; then
> > ELEMENT=.
> > fi
> >
> > So PATCH 1 actually fixes this, the size impact is huge
> > and therefore it is dependent on CONFIG_DEKTOP:
> Why is the size impact so huge? Why don't you use the equivalent of the
> script, if ELEMENT empty the ELEMENT="."?
Hi,
because it is tricky to perform the same thing that IFS=: does.
> I think the line
>
> if (*p == ':' && p[1] != '.')
> is even wrong and should be
> if (*p == ':')
No, if you remove && p[1] != '.' it will process
also a PATH=:: that were transformed to PATH=:.:
in the previous pass.
> What about this change:
>
> while (p) {
> n = strchr(p, ':');
> if (n)
> *n++ = '\0';
> + if (*p == '\0')
> + p = ".";
> - if (*p != '\0') { /* it's not a PATH="foo::bar"
> situation */
> ...
> - }
> The size impact should be the assignment 'p = "."' and the constant ".",
> about 10 bytes total, no extra processing, no extra malloc.
>
I also thought it was that easy in the beginning, but if I recall it
correctly in this way it was not working. With your changes:
export PATH=:/usr/local/bin:/usr/bin:/bin::/usr/local/games:/usr/games:
debian:~/Desktop/SourceCode/busybox$ ./busybox which -a busybox
/bin/busybox
but it should show also 3 times the busybox binary in the cwd.
./busybox which -a busybox
before p
after p ./usr/local/bin:/usr/bin:/bin::/usr/local/games:/usr/games:
after concat p
'./usr/local/bin:/usr/bin:/bin::/usr/local/games:/usr/games:/busybox'
before p /usr/local/bin
after p /usr/local/bin
after concat p '/usr/local/bin/busybox'
before p /usr/bin
after p /usr/bin
after concat p '/usr/bin/busybox'
before p /bin
after p /bin
after concat p '/bin/busybox'
execable p '/bin/busybox'
/bin/busybox
before p
after p ./usr/local/games:/usr/games:
after concat p './usr/local/games:/usr/games:/busybox'
before p /usr/local/games
after p /usr/local/games
after concat p '/usr/local/games/busybox'
before p /usr/games
after p /usr/games
after concat p '/usr/games/busybox'
before p
after p .
after concat p './busybox'
it misses the leading and double colon because it doesn't cut the string
at the right place. It should show the trailing : but execable_file fails
for some reason that i'm to tired to investigate now.
Ciao,
Tito
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