Avoid bad breakpoints with --gc-sections

We found a case where --gc-sections can cause gdb to set an invalid
breakpoint.  In the included test case, gdb will set a breakpoint with
two locations, one of which is 0x0.

The code in lnp_state_machine::check_line_address is intended to
filter out this sort of problem, but in this case, the entire CU is
empty, causing unrelocated_lowpc==0x0 -- which circumvents the check.

It seems to me that if a CU is empty like this, then it is ok to
simply ignore the line table, as there won't be any locations anyway.

1 files changed, 7 insertions, 2 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 3fe6c3a..f7cb95b 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -10630,8 +10630,13 @@ read_file_scope (struct die_info *die, struct dwarf2_cu *cu)
 
   /* Decode line number information if present.  We do this before
      processing child DIEs, so that the line header table is available
-     for DW_AT_decl_file.  */
-  handle_DW_AT_stmt_list (die, cu, fnd, lowpc);
+     for DW_AT_decl_file.  The PC check is here because, if LOWPC and
+     HIGHPC are both 0x0, then there won't be any interesting code in
+     the CU, but a check later on (in
+     lnp_state_machine::check_line_address) will fail to properly
+     exclude an entry that was removed via --gc-sections.  */
+  if (lowpc != highpc)
+    handle_DW_AT_stmt_list (die, cu, fnd, lowpc);
 
   /* Process all dies in compilation unit.  */
   if (die->child != NULL)