From jeff.horner at vanderbilt.edu  Sat Mar 24 23:02:29 2007
From: jeff.horner at vanderbilt.edu (Jeffrey Horner)
Date: Sat, 24 Mar 2007 17:02:29 -0500
Subject: [Rd] Subtle bug in do_basename
Message-ID: <46059FF5.409@vanderbilt.edu>

Hello,


I've been wondering why my no-optimization R-devel builds have been 
hanging during "building/updating package indices ...". I tracked it 
down with gdb to this line from do_basename in utils.c:

while ( *(p = buf + strlen(buf) - 1) == fsp ) *p = '\0';

Now, imagine if your compiler places the variable fsp immediately before 
buf on the stack, and strlen(buf) is 0. Yup, you get an infinite loop 
because p will always be assigned the address of fsp. I'm not quite sure 
what happens when the stack variables are ordered in a different 
configuration, probably something bad?

Here's a quick fix, but maybe someone would want to find a better one:

$ svn diff src/main/util.c
Index: src/main/util.c
===================================================================
--- src/main/util.c     (revision 40876)
+++ src/main/util.c     (working copy)
@@ -694,7 +694,8 @@
         R_fixslash(buf);
  #endif
         /* remove trailing file separator(s) */
-       while ( *(p = buf + strlen(buf) - 1) == fsp ) *p = '\0';
+       if(strlen(p))
+           while ( *(p = buf + strlen(buf) - 1) == fsp ) *p = '\0';
         if ((p = Rf_strrchr(buf, fsp)))
             p++;
         else

Best,

Jeff
-- 
http://biostat.mc.vanderbilt.edu/JeffreyHorner



[Rd] Subtle bug in do_basename
Jeffrey Horner