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[PATCH 2/5] Don't memcpy non-trivially-copyable types: Make enum_flags triv. copyable
- From: Pedro Alves <palves at redhat dot com>
- To: gdb-patches at sourceware dot org
- Date: Thu, 13 Apr 2017 03:27:52 +0100
- Subject: [PATCH 2/5] Don't memcpy non-trivially-copyable types: Make enum_flags triv. copyable
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The delete-memcpy-with-non-trivial-types patch exposed many instances
of this problem:
src/gdb/btrace.h: In function ‘btrace_insn_s* VEC_btrace_insn_s_quick_insert(VEC_btrace_insn_s*, unsigned int, const btrace_insn_s*, const char*, unsigned int)’:
src/gdb/common/vec.h:948:62: error: use of deleted function ‘void* memmove(T*, const U*, size_t) [with T = btrace_insn; U = btrace_insn; <template-parameter-1-3> = void; size_t = long unsigned int]’
memmove (slot_ + 1, slot_, (vec_->num++ - ix_) * sizeof (T)); \
^
src/gdb/common/vec.h:436:1: note: in expansion of macro ‘DEF_VEC_FUNC_O’
DEF_VEC_FUNC_O(T) \
^
src/gdb/btrace.h:84:1: note: in expansion of macro ‘DEF_VEC_O’
DEF_VEC_O (btrace_insn_s);
^
[...]
src/gdb/common/vec.h:1060:31: error: use of deleted function ‘void* memcpy(T*, const U*, size_t) [with T = btrace_insn; U = btrace_insn; <template-parameter-1-3> = void; size_t = long unsigned int]’
sizeof (T) * vec2_->num); \
^
src/gdb/common/vec.h:437:1: note: in expansion of macro ‘DEF_VEC_ALLOC_FUNC_O’
DEF_VEC_ALLOC_FUNC_O(T) \
^
src/gdb/btrace.h:84:1: note: in expansion of macro ‘DEF_VEC_O’
DEF_VEC_O (btrace_insn_s);
^
So, VECs (given it's C roots) rely on memcpy/memcpy of VEC elements to
be well defined, in order to grow/reallocate its internal elements
array. This means that we can only put trivially copyable types in
VECs. E.g., if a type requires using a custom copy/move ctor to
relocate, then we can't put it in a VEC (so we use std::vector
instead). But, as shown above, we're violating that requirement.
btrace_insn is currently not trivially copyable, because it contains
an enum_flags field, and that is itself not trivially copyable. This
patch corrects that.
Note that std::vector relies on std::is_trivially_copyable too to know
whether it can reallocate its elements with memcpy/memmove instead of
having to call copy/move ctors and dtors, so if we have types in
std::vectors that weren't trivially copyable because of enum_flags,
this will make such vectors more efficient.
gdb/ChangeLog:
yyyy-mm-dd Pedro Alves <palves@redhat.com>
* common/enum-flags.h (enum_flags): Define copy/move ctors/op= as
defaulted.
---
gdb/common/enum-flags.h | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)
diff --git a/gdb/common/enum-flags.h b/gdb/common/enum-flags.h
index e63c8a4..bea0ad5 100644
--- a/gdb/common/enum-flags.h
+++ b/gdb/common/enum-flags.h
@@ -120,15 +120,12 @@ public:
: m_enum_value ((enum_type) 0)
{}
- enum_flags (const enum_flags &other)
- : m_enum_value (other.m_enum_value)
- {}
-
- enum_flags &operator= (const enum_flags &other)
- {
- m_enum_value = other.m_enum_value;
- return *this;
- }
+ /* Define copy/move ctor/op= as defaulted so that enum_flags is
+ trivially copyable. */
+ enum_flags (const enum_flags &other) = default;
+ enum_flags (enum_flags &&) noexcept = default;
+ enum_flags &operator= (const enum_flags &other) = default;
+ enum_flags &operator= (enum_flags &&) = default;
/* If you get an error saying these two overloads are ambiguous,
then you tried to mix values of different enum types. */
--
2.5.5