Correctly handle DW_LLE_start_end

When the code to handle DW_LLE_start_end was added (as part of some
DWARF 5 work), it was written to add the base address.  However, this
seems incorrect -- the DWARF standard describes this as an address,
not an offset from the base address.

This patch changes a couple of spots in dwarf2/loc.c to fix this
problem.  It then changes decode_debug_loc_addresses to return
DEBUG_LOC_OFFSET_PAIR instead, which preserves the previous semantics.

This only showed up on the RISC-V target internally, due to the
combination of DWARF 5 and a newer version of GCC.  I've updated a
couple of existing loclists test cases to demonstrate the bug.

diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index eb128fa5fc6fe76352611821cee814da9465293d..b5936e13eee2971bfd701d052c85bfd12d96055f 100644 (file)
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -139,7 +139,9 @@ decode_debug_loc_addresses (const gdb_byte *loc_ptr, const gdb_byte *buf_end,
   if (*low == 0 && *high == 0)
     return DEBUG_LOC_END_OF_LIST;
 
-  return DEBUG_LOC_START_END;
+  /* We want the caller to apply the base address, so we must return
+     DEBUG_LOC_OFFSET_PAIR here.  */
+  return DEBUG_LOC_OFFSET_PAIR;
 }
 
 /* Decode the addresses in .debug_loclists entry.
@@ -416,13 +418,15 @@ dwarf2_find_location_expression (struct dwarf2_loclist_baton *baton,
         .debug_addr which already has the DWARF "base address". We still add
         base_offset in case we're debugging a PIE executable. However, if the
         entry is DW_LLE_offset_pair from a DWO, add the base address as the
-        operands are offsets relative to the applicable base address.  */
+        operands are offsets relative to the applicable base address.
+        If the entry is DW_LLE_start_end or DW_LLE_start_length, then
+        it already is an address, and we don't need to add the base.  */
       if (baton->from_dwo && kind != DEBUG_LOC_OFFSET_PAIR)
        {
          low += base_offset;
          high += base_offset;
        }
-      else
+      else if (kind == DEBUG_LOC_OFFSET_PAIR)
        {
          low += base_address;
          high += base_address;
@@ -3983,8 +3987,11 @@ loclist_describe_location (struct symbol *symbol, CORE_ADDR addr,
        }
 
       /* Otherwise, a location expression entry.  */
-      low += base_address;
-      high += base_address;
+      if (kind == DEBUG_LOC_OFFSET_PAIR)
+       {
+         low += base_address;
+         high += base_address;
+       }
 
       low = gdbarch_adjust_dwarf2_addr (gdbarch, low);
       high = gdbarch_adjust_dwarf2_addr (gdbarch, high);

diff --git a/gdb/testsuite/gdb.dwarf2/loclists-multiple-cus.exp b/gdb/testsuite/gdb.dwarf2/loclists-multiple-cus.exp
index 7844628bc168933f3d385394e4b3bdf3d4d694e0..a7af7fd05371338709bcd5f05afdeb464c5eeb14 100644 (file)
--- a/gdb/testsuite/gdb.dwarf2/loclists-multiple-cus.exp
+++ b/gdb/testsuite/gdb.dwarf2/loclists-multiple-cus.exp
@@ -1,4 +1,4 @@
-# Copyright 2020 Free Software Foundation, Inc.
+# Copyright 2020, 2021 Free Software Foundation, Inc.
 
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -105,6 +105,9 @@ foreach_with_prefix is_64 {false true} {
 
                # For variable foo.
                list_ {
+                   # This should not affect the following addresses.
+                   base_address 0xffff
+
                    # When in func1.
                    start_length $func1_addr $func1_len {
                        DW_OP_constu 0x123456

diff --git a/gdb/testsuite/gdb.dwarf2/loclists-start-end.exp b/gdb/testsuite/gdb.dwarf2/loclists-start-end.exp
index e3c12e5093ff22d524219181cb9066a40630d7b9..18ef2bfaf90e80399adef23aa3942271b9f6f5b9 100644 (file)
--- a/gdb/testsuite/gdb.dwarf2/loclists-start-end.exp
+++ b/gdb/testsuite/gdb.dwarf2/loclists-start-end.exp
@@ -96,6 +96,9 @@ foreach_with_prefix is_64 {false true} {
 
                # For variable foo.
                list_ {
+                   # This should not affect the following addresses.
+                   base_address 0xffff
+
                    # When in func1.
                    start_end $func1_addr "$func1_addr + $func1_len" {
                        DW_OP_constu 0x123456

diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index b48cfad3b9e5da97984607332cc204996d8cc907..774cac712a2043e54c3e841046b50748cd47b4a3 100644 (file)
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -1894,9 +1894,10 @@ namespace eval Dwarf {
        define_label $list_label
 
        with_override Dwarf::start_length Dwarf::_loclists_start_length {
+       with_override Dwarf::base_address Dwarf::_loclists_base_address {
        with_override Dwarf::start_end Dwarf::_loclists_start_end {
            uplevel $body
-       }}
+       }}}
 
        # Emit end of list.
        _op .byte 0x00 "DW_LLE_end_of_list"
@@ -1972,6 +1973,15 @@ namespace eval Dwarf {
        incr _debug_loclists_locdesc_count
     }
 
+    # Emit a DW_LLE_base_address entry.
+    proc _loclists_base_address {addr} {
+       variable _debug_loclists_addr_size
+       variable _debug_loclists_locdesc_count
+       _op .byte 0x06 "DW_LLE_base_address"
+       _op .${_debug_loclists_addr_size}byte $addr "base_address"
+       incr _debug_loclists_locdesc_count
+    }
+
     # Emit a DWARF .debug_line unit.
     # OPTIONS is a list with an even number of elements containing
     # option-name and option-value pairs.