On Tue, Jan 06, 2015 at 08:50:58AM -0500, Paul Smith wrote: > On Tue, 2015-01-06 at 09:43 +0100, Jakub Jelinek wrote: > > On Tue, Jan 06, 2015 at 03:18:48AM -0500, Paul Smith wrote: > > > Hi all. It's possible my code is doing something illegal, but it's also > > > possible I've found a problem with -O3 optimization in GCC 4.9.2. I've > > > built this same code with GCC 4.8.2 -O3 on GNU/Linux and it works fine. > > > It also works with GCC 4.9.2 with lower -O (-O2 for example). > > > > Your testcase is invalid. > > GCC trunk -fsanitize=undefined (in particular -fsanitize=nonnull-attribute) > > diagnoses it: > > /tmp/mystring.cpp:103:26: runtime error: null pointer passed as argument 2, > > which is declared to never be null > > LD_PRELOAD=libmemstomp.so detects it too. > > > > Calling memcpy (p, NULL, 0); is invalid according to C and C++ > > standards, you need to guard it, e.g. with if (data) memcpy (p, data, len1); > > or if (len1) memcpy (p, data, len1); > > Ah interesting. You're right, this is definitely not correct. But > since len1 is 0 in this case, no implementation of memcpy() actually > tried to dereference the data pointer and so there was no failure (we > build and test with clang on OSX and MSVC on Windows, and run with > valgrind and ASAN (clang)). > > I'll have to look at other possible failure situations.
Note, it is even mentioned in GCC 4.9 porting to documentation: https://gcc.gnu.org/gcc-4.9/porting_to.html Jakub
