Ignore 0,0 entries in .debug_aranges

When running the internal AdaCore test suite against the new DWARF
indexer, I found one regression on RISC-V.  The test in question uses
--gc-sections, and winds up with an entry in the middle of a
.debug_aranges that has both address and length of 0.  In this
scenario, gdb assumes the entries are terminated and then proceeds to
reject the section because it reads a subsequent entry as if it were a
header.

It seems to me that, because each header describes the size of each
.debug_aranges CU, it's better to simply ignore 0,0 entries and simply
read to the end.  That is what this patch does.

I've patched an existing test to provide a regression test for this.

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 698720276a91ac646bd5bc736dd1c3c4792e8349..6dcd446e5f464156f0641d9e242b5226e38e59ce 100644 (file)
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -2469,7 +2469,7 @@ read_addrmap_from_aranges (dwarf2_per_objfile *per_objfile,
         bytes.  */
       addr += (entry_end - addr) % (2 * address_size);
 
-      for (;;)
+      while (addr < entry_end)
        {
          if (addr + 2 * address_size > entry_end)
            {
@@ -2487,7 +2487,14 @@ read_addrmap_from_aranges (dwarf2_per_objfile *per_objfile,
                                                      dwarf5_byte_order);
          addr += address_size;
          if (start == 0 && length == 0)
-           break;
+           {
+             /* This can happen on some targets with --gc-sections.
+                This pair of values is also used to mark the end of
+                the entries for a given CU, but we ignore it and
+                instead handle termination using the check at the top
+                of the loop.  */
+             continue;
+           }
          if (start == 0 && !per_bfd->has_section_at_zero)
            {
              /* Symbol was eliminated due to a COMDAT group.  */

diff --git a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
index 67e96fb1128ade51c95e63ae549bf14de746d864..adb4e0a4c21f2f5de9ef3acb22045d4d899de09f 100644 (file)
--- a/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
+++ b/gdb/testsuite/gdb.dwarf2/locexpr-data-member-location.exp
@@ -296,6 +296,9 @@ Dwarf::assemble ${asm_file} {
     }
 
     aranges {} cu_label {
+       # This 0,0 entry tests that the .debug_aranges reader can
+       # handle an apparent terminator before the end of the ranges.
+       arange {} 0 0
        arange {} $foo_start $foo_end
        arange {} $bar_start $bar_end
     }