[patch / rfc / 5.3] Attempt N++ for gdb_realpath()

[Andrew Cagney <ac131313@redhat.com>]

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Hello,

This is trying to fix 
http://sources.redhat.com/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gdb&pr=656

It breaks the host system down into:

- realpath() and constant pathmax

- canonicalize file name

- realpath() and pathconf()

- xstrdup()

realpath() is split into two cases - the easy / common one and the nasty 
horrible pathconf() one.  The latter (which was causing grief on GNU) 
has been moved to the end.

comments?  For 5.3 and mainline.

Andrew

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2002-11-09  Andrew Cagney  <ac131313@redhat.com>

	* utils.c (gdb_realpath): Rewrite.  Try realpath() with a constant
	buffer, cannonicalize_file_name(), realpath() with a pathconf()
	defined buffer, xstrdup().

Index: utils.c
===================================================================
RCS file: /cvs/src/src/gdb/utils.c,v
retrieving revision 1.76
diff -p -r1.76 utils.c
*** utils.c	1 Aug 2002 17:18:33 -0000	1.76
--- utils.c	11 Nov 2002 16:33:36 -0000
*************** string_to_core_addr (const char *my_stri
*** 2534,2564 ****
  char *
  gdb_realpath (const char *filename)
  {
  #if defined(HAVE_REALPATH)
  # if defined (PATH_MAX)
!   char buf[PATH_MAX];
  #  define USE_REALPATH
  # elif defined (MAXPATHLEN)
!   char buf[MAXPATHLEN];
! #  define USE_REALPATH
! # elif defined (HAVE_UNISTD_H) && defined(HAVE_ALLOCA)
!   char *buf = alloca ((size_t)pathconf ("/", _PC_PATH_MAX));
  #  define USE_REALPATH
  # endif
  #endif /* HAVE_REALPATH */
  
! #if defined(USE_REALPATH)
!   char *rp = realpath (filename, buf);
!   return xstrdup (rp ? rp : filename);
! #elif defined(HAVE_CANONICALIZE_FILE_NAME)
!   char *rp = canonicalize_file_name (filename);
!   if (rp == NULL)
!     return xstrdup (filename);
!   else
!     return rp;
! #else
!   return xstrdup (filename);
  #endif
  }
  
  /* Return a copy of FILENAME, with its directory prefix canonicalized
--- 2534,2597 ----
  char *
  gdb_realpath (const char *filename)
  {
+   /* Method 1: The system has a compile time upper bound on a filename
+      path.  Use that and realpath() to canonicalize the name.  This is
+      the most common case.  Note that, if there isn't a compile time
+      upper bound, you want to avoid realpath() at all costs.  */
  #if defined(HAVE_REALPATH)
+   {
  # if defined (PATH_MAX)
!     char buf[PATH_MAX];
  #  define USE_REALPATH
  # elif defined (MAXPATHLEN)
!     char buf[MAXPATHLEN];
  #  define USE_REALPATH
  # endif
+ # if defined (USE_REALPATH)
+     char *rp = realpath (filename, buf);
+     if (rp == NULL)
+       rp = filename;
+     return xstrdup (rp);
+   }
+ # endif
  #endif /* HAVE_REALPATH */
  
!   /* Method 2: The host system (i.e., GNU) has the function
!      canonicalize_file_name() which malloc's a chunk of memory and
!      returns that, use that.  */
! #if defined(HAVE_CANONICALIZE_FILE_NAME)
!   {
!     char *rp = canonicalize_file_name (filename);
!     if (rp == NULL)
!       return xstrdup (filename);
!     else
!       return rp;
!   }
  #endif
+ 
+   /* Method 3: Now we're getting desperate!  The system doesn't have a
+      compile time buffer size and no alternative function.  Query the
+      OS, using pathconf(), for the buffer limit.  Care is needed
+      though, some systems do not limit PATH_MAX (return -1 for
+      pathconf()) making it impossible to pass a correctly sized buffer
+      to realpath() (it could always overflow).  On those systems, we
+      skip this.  */
+ #if defined (HAVE_REALPATH) && defined (HAVE_UNISTD_H) && defined(HAVE_ALLOCA)
+   {
+     /* Find out the max path size.  */
+     long path_max = pathconf ("/", _PC_PATH_MAX);
+     if (path_max > 0)
+       {
+ 	/* PATH_MAX is bounded.  */
+ 	char *buf = alloca (path_max);
+ 	char *rp = realpath (filename, buf);
+ 	return xstrdup (rp ? rp : filename);
+       }
+   }
+ #endif
+ 
+   /* This system is a lost cause, just dup the buffer.  */
+   return xstrdup (filename);
  }
  
  /* Return a copy of FILENAME, with its directory prefix canonicalized