Allow Java's ELF symtab reader to use separate debuginfo files

[Andrew Haley]

Testing revealed a couple of failures with separate debuginfo.
I made a silly off-by-one error and I missed a null pointer check.

Fixed, pushed.

Andrew.


2009-12-16  Andrew Haley  <aph at redhat.com>

	* openjdk/hotspot/agent/src/os/linux/symtab.c (open_file_from_debug_link):
	Check for NULL.
	Fix off by one error in aligning the CRC: the offset is 4 bytes,
	not 3.

--- openjdk/hotspot/agent/src/os/linux/symtab.c~	2009-12-11 16:33:49.926655750 +0000
+++ openjdk/hotspot/agent/src/os/linux/symtab.c	2009-12-16 16:08:22.525718029 +0000
@@ -198,11 +198,13 @@
 				     ELF_SHDR *shbuf,
 				     struct elf_section *scn_cache)
 {
+  int debug_fd;
   struct elf_section *debug_link = find_section_by_name(".gnu_debuglink", fd, ehdr,
 							shbuf, scn_cache);
-  int debug_fd;
+  if (debug_link == NULL)
+    return -1;
   char *debug_filename = debug_link->c_data;
-  int offset = strlen(debug_filename) + 3 >> 2;
+  int offset = (strlen(debug_filename) + 4) >> 2;
   static unsigned int crc;
   crc = ((unsigned int*)debug_link->c_data)[offset];
   char *debug_pathname = malloc(strlen(debug_filename)