[Patch] Improve path lookup of absolute source file

[Francois Rigault <francois.rigault@amadeus.com>]

When setting breakpoints on a source file using an absolute path,
lookup_symtab will try to match the target source file path with each
symbol file path. For each of these paths, the realpath function is
called, potentially leading to a big number of IOs.

On a slow IO filesystem, like a network file system, this can slow down
the performances. gdb takes here 15s to complete the setting of the
first breakpoint on an absolute source file path.

In order to let gdb find the files without generating IOs, a simple
trick is to check that symbol source file and target source file have
the same basename, as source file used at compilation time and the one
used for debugging are unlikely to have different basenames. See the
patch below against gdb-6.8.

Regards




*** gdb/symtab.c        Thu Sep 11 11:10:13 2008
--- gdb/symtab.c        Thu Sep 11 11:31:46 2008
*************** lookup_partial_symtab (const char *name)
*** 259,264 ****
--- 259,270 ----
        return (pst);
        }
 
+     /* Skip this symbol if basenames differ. */
+     if (FILENAME_CMP (lbasename(name), lbasename(pst->filename)) != 0)
+       {
+       continue;
+       } 
+ 
      /* If the user gave us an absolute path, try to find the file in
         this symtab and use its absolute path.  */
      if (full_path != NULL)