infinite loop in prompt expansion

infinite loop in prompt expansion

[Laurent Wacrenier]

Prompt truncation may enter in infinite loop within litteral escape
sequence :

% print -P %/
/home/lwa
% print -P '%{%80<..<%/%}'
/home/lwa
% print -P '%8<..<%/'
..me/lwa
% print -P '%{%8<..<%/%}'
(don't give the hand back and spend all CPU time)

Tested on zsh 3.1.9 and 4.0.6

GDB output :

prompttrunc (arg=6, truncchar=134574132, doprint=1, endchar=0) at prompt.c:852
852                             if (*p == Inpar)
(gdb) where
#0  prompttrunc (arg=6, truncchar=134574132, doprint=1, endchar=0)
    at prompt.c:852
#1  0x280c0685 in putpromptchar (doprint=1, endchar=0) at prompt.c:443
#2  0x280bfcfc in promptexpand (s=0x80639a0 "%{%8<..<%/%}", ns=0, 
    rs=0x61 <Error reading address 0x61: Bad address>, 
    Rs=0x61 <Error reading address 0x61: Bad address>) at prompt.c:177
#3  0x2807eb8c in bin_print (name=0x8063970 "print", args=0xbfbff110, 
    ops=0xbfbff160 "", func=13) at builtin.c:2917
#4  0x2807768d in execbuiltin (args=0x8063940, bn=0x280db16c) at builtin.c:367
#5  0x2808889d in execcmd (state=0xbfbff470, input=0, output=0, how=18, 
    last1=2) at exec.c:2296
#6  0x28085cf4 in execpline2 (state=0xbfbff470, pcode=259, how=18, input=0, 
    output=0, last1=0) at exec.c:1201
#7  0x2808536d in execpline (state=0xbfbff470, slcode=97, how=18, last1=0)
    at exec.c:991
#8  0x28084d3a in execlist (state=0xbfbff470, dont_change_job=0, exiting=0)
    at exec.c:826
#9  0x28084a5f in execode (p=0x61, dont_change_job=97, exiting=97)
    at exec.c:729
#10 0x280987b4 in loop (toplevel=1, justonce=0) at init.c:165
#11 0x2809b054 in zsh_main (argc=1, argv=0xbfbff544) at init.c:1215
#12 0x0804852b in exit ()
#13 0x08048455 in exit ()
(gdb) s
857                             else if (w) {
(gdb) 
852                             if (*p == Inpar)
(gdb) 
857                             else if (w) {
(gdb) 
852                             if (*p == Inpar)
(gdb) 
857                             else if (w) {
(gdb) 
852                             if (*p == Inpar)
(gdb) print p
$1 = 0x8057034 "\211"
(gdb) print w
$2 = 0

PATCH Re: infinite loop in prompt expansion

[Bart Schaefer]

On Sep 30,  4:51pm, Laurent Wacrenier wrote:
} Subject: infinite loop in prompt expansion
}
} Prompt truncation may enter in infinite loop within litteral escape
} sequence :
} 
} % print -P '%{%8<..<%/%}'
} (don't give the hand back and spend all CPU time)

It shouldn't infinte loop, but I'd like to point out that it also is not
intended to do anything useful.

%{ ... %} means that the string inside the braces is treated as zero width
for purposes of computing the size of the prompt.  Truncating a zero width 
string is a no-op.

Hence the fix (which is probably not going to make you happy) is this:

Index: prompt.c
===================================================================
RCS file: /extra/cvsroot/zsh/zsh-4.0/Src/prompt.c,v
retrieving revision 1.6
diff -c -r1.6 prompt.c
--- prompt.c	1 Sep 2002 16:47:38 -0000	1.6
+++ prompt.c	30 Sep 2002 18:31:15 -0000
@@ -856,6 +856,10 @@
 	    addbufspc(1);
 	    *bp++ = *fm++;
 	}
+	if (dontcount) {
+	    bp = buf + w;
+	    return 1;
+	}
 	if (!*fm)
 	    return 0;
 	if (bp - buf == w && truncchar == ']') {

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Zsh: http://www.zsh.org | PHPerl Project: http://phperl.sourceforge.net   

Re: PATCH Re: infinite loop in prompt expansion

[Laurent Wacrenier]

Le Lun 30 sep 18:32:30 2002, Bart Schaefer écrit:
> It shouldn't infinte loop, but I'd like to point out that it also is not
> intended to do anything useful.

This may have a sense within PS1 to set a xterm title or a terminal
status line.

> Hence the fix (which is probably not going to make you happy) is this:

Well... that's not what's wroten in the manual.

% print -P '%{%8<..<%/%}'
/home/lwa

Re: PATCH Re: infinite loop in prompt expansion

[Bart Schaefer]

On Oct 1, 11:35am, Laurent Wacrenier wrote:
} Subject: Re: PATCH Re: infinite loop in prompt expansion
}
} Le Lun 30 sep 18:32:30 2002, Bart Schaefer écrit:
} > It shouldn't infinte loop, but I'd like to point out that it also is
} > not intended to do anything useful.
}
} This may have a sense within PS1 to set a xterm title or a terminal
} status line.

I guessed that was what you wanted, but it doesn't work.

Consider what happens when you put the %8<..< *outside* the %{ %} like so:

% print -P '%8<..<%{%/%}987654321'
../home/lwa654321

The manual says:
  "The string within the braces should not change the cursor position."

Therefore zsh counts zero characters for everything from the %{ through
the matching %}, and applies the truncation to whatever comes after it.

Even when the %8<..< is put inside the braces, zsh is still counting zero
characters for everything through the ending %}.  That's what confuses
the truncation code into going into an infinite loop.
 
} > Hence the fix (which is probably not going to make you happy) is this:
} 
} Well... that's not what's wroten in the manual.

The manual says:

     "The part of the prompt string to be truncated runs to the end of
     the string, or to the end of the next enclosing group of the `%('
     construct, or to the next truncation encountered at the same
     grouping level (i.e. truncations inside a `%(' are separate), which
     ever comes first."

Note that it *doesn't* say that it ends at the closing %} that matches a
preceding %{.

I think I've got a patch (by introducing Yet Another Global) that will
allow that to work, but I'd like to hear more zsh-workers' opinions first.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Zsh: http://www.zsh.org | PHPerl Project: http://phperl.sourceforge.net