On Jan 22, 2020, Jonathan Wakely <jwak...@redhat.com> wrote:
>>> I don't think so, that wouldn't work. I think pos02 could just be
>>> removed from the test.
>> Will do.
> Thanks, OK to commit.
Thanks, here's what I tested and am about to install.
tolerate padding in mbstate_t
From: Alexandre Oliva <ol...@adacore.com>
Padding in mbstate_t objects may get the memcmp to fail.
Attempt to avoid the failure with zero initialization.
for libstdc++-v3/ChangeLog
* testsuite/27_io/fpos/mbstate_t/1.cc: Zero-init mbstate_t.
---
libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc | 28 +++++++++++++++++-----
1 file changed, 21 insertions(+), 7 deletions(-)
diff --git a/libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc
b/libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc
index f92d68f..28fec8e 100644
--- a/libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc
+++ b/libstdc++-v3/testsuite/27_io/fpos/mbstate_t/1.cc
@@ -28,24 +28,38 @@
void test01()
{
typedef std::mbstate_t state_type;
- state_type state01 = state_type();
- state_type state02 = state_type();
+ // Use zero-initialization of the underlying memory so that padding
+ // bytes, if any, stand a better chance of comparing the same.
+ // Zero-initialized memory is guaranteed to be a valid initial
+ // state. This doesn't quite guarantee that any padding bits won't
+ // be overwritten when copying from other instances that haven't
+ // been fully initialized: this data type is compatible with C, so
+ // it is likely plain old data, but it could have a default ctor
+ // that initializes only the relevant fields, whereas copy-ctor and
+ // operator= could be implemented as a full-object memcpy, including
+ // padding bits, rather than fieldwise copying. However, since
+ // we're comparing two values copied from the same state_type
+ // instance, if padding bits are copied, we'll get the same for both
+ // of them, and if they aren't, we'll keep the values we initialized
+ // them with, so this should be good.
+ state_type state[2];
+ std::memset(state, 0, sizeof (state));
+
std::streampos pos01(0);
- std::streampos pos02(0);
// 27.4.3.1 fpos members
// void state(state_type s);
// state_type state();
// XXX Need to have better sanity checking for the mbstate_t type,
- // or whatever the insantiating type for class fpos happens to be
+ // or whatever the instantiating type for class fpos happens to be
// for streampos, as things like equality operators and assignment
// operators, increment and deincrement operators need to be in
// place.
- pos01.state(state02);
- state01 = pos01.state();
- VERIFY( std::memcmp(&state01, &state02, sizeof(state_type)) == 0 );
+ pos01.state(state[1]);
+ state[0] = pos01.state();
+ VERIFY( std::memcmp(&state[0], &state[1], sizeof(state_type)) == 0 );
}
int main()
--
Alexandre Oliva, freedom fighter he/him https://FSFLA.org/blogs/lxo
Free Software Evangelist Stallman was right, but he's left :(
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