RFC: fix PR gdb/15538

[Tom Tromey <tromey@redhat.com>]

This fixes PR 15538, an assertion failure when reading a certain file.

The bug is that dwarf2_record_block_ranges asserts that the ranges
section has been read in -- but it can be called without this occurring.

The fix is to simply read in the section in dwarf2_record_block_ranges.

I didn't know how to make a test case, so I haven't provided one.
If this is an issue I will try harder to figure it out.

Built and regtested on x86-64 Fedora 18.
The bug reporter also tested it.

Tom

    	PR gdb/15538:
    	* dwarf2read.c (dwarf2_record_block_ranges): Ensure that the
    	ranges section has been read.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 8947f8f..64fc7da 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -10458,7 +10458,7 @@ dwarf2_record_block_ranges (struct die_info *die, struct block *block,
          address range list in the .debug_ranges section.  */
       unsigned long offset = (DW_UNSND (attr)
 			      + (need_ranges_base ? cu->ranges_base : 0));
-      const gdb_byte *buffer = dwarf2_per_objfile->ranges.buffer + offset;
+      const gdb_byte *buffer;
 
       /* For some target architectures, but not others, the
          read_address function sign-extends the addresses it returns.
@@ -10477,7 +10477,7 @@ dwarf2_record_block_ranges (struct die_info *die, struct block *block,
       CORE_ADDR base = cu->base_address;
       int base_known = cu->base_known;
 
-      gdb_assert (dwarf2_per_objfile->ranges.readin);
+      dwarf2_read_section (objfile, &dwarf2_per_objfile->ranges);
       if (offset >= dwarf2_per_objfile->ranges.size)
         {
           complaint (&symfile_complaints,
@@ -10485,6 +10485,7 @@ dwarf2_record_block_ranges (struct die_info *die, struct block *block,
                      offset);
           return;
         }
+      buffer = dwarf2_per_objfile->ranges.buffer + offset;
 
       for (;;)
         {