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[gdb/build] Fix Wmaybe-uninitialized in gdb_optional.h

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When building with CFLAGS/CXXFLAGS="-O2 -g -Wall", we run into:
...
In file included from src/gdb/exceptions.h:23,
                 from src/gdb/utils.h:24,
                 from src/gdb/defs.h:630,
                 from src/gdb/record-btrace.c:22:
src/gdb/ui-out.h: In function 'void btrace_insn_history(ui_out*, \
  const btrace_thread_info*, const btrace_insn_iterator*, \
  const btrace_insn_iterator*, gdb_disassembly_flags)':
src/gdb/ui-out.h:352:18: warning: \
  'asm_list.ui_out_emit_type<ui_out_type_list>::m_uiout' may be used \
  uninitialized in this function [-Wmaybe-uninitialized]
  352 |     m_uiout->end (Type);
      |     ~~~~~~~~~~~~~^~~~~~
src/gdb/record-btrace.c:795:35: note: \
  'asm_list.ui_out_emit_type<ui_out_type_list>::m_uiout' was declared here
  795 |   gdb::optional<ui_out_emit_list> asm_list;
      |                                   ^~~~~~~~
...

This is reported as PR gcc/80635 - "[8/9/10/11 regression] std::optional and
bogus -Wmaybe-uninitialized warning".

Silence the warning by using the workaround suggested here (
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80635#c53 ):
...
   union
   {
     struct { } m_dummy;
     T m_item;
+    volatile char dont_use; // Silences -Wmaybe-uninitialized warning.
   };
...

Build on x86_64-linux.

gdbsupport/ChangeLog:

2020-07-28  Tom de Vries  <tdevries@suse.de>

	PR build/26281
	* gdb_optional.h (class optional): Add volatile member to union
	contaning m_dummy and m_item.
This commit is contained in:
Tom de Vries 2020-07-28 15:07:44 +02:00
parent d70f978b44
commit 866b34a12d
2 changed files with 8 additions and 0 deletions
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6
gdbsupport/ChangeLog
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@ -1,3 +1,9 @@
2020-07-28 Tom de Vries <tdevries@suse.de>
PR build/26281
* gdb_optional.h (class optional): Add volatile member to union
contaning m_dummy and m_item.
2020-07-17 Andrew Burgess <andrew.burgess@embecosm.com>
* tdesc.h (struct target_desc_deleter): Moved here

2
gdbsupport/gdb_optional.h
View File

@ -208,6 +208,8 @@ private:
{
struct { } m_dummy;
T m_item;
volatile char dont_use; /* Silences -Wmaybe-uninitialized warning, see
PR gcc/80635. */
};
/* True if the object was ever emplaced. */