Methods like Address::SetOffset and Address::Slide seem to have data races despite m_offset being atomic. Callers of those methods would have to guarantee that nothing else is trying to write to m_offset. And if they're doing that, then there doesn't appear to be a need for std::atomic on that field.
BTW, I propose we move the member variables from protected to private. As far as I can tell, there aren't any derived classes (yet), at least none that access those members. If we need to add a mutex to the class itself, it'll be better if any future derived classes access the data through accessors. On Fri, Aug 26, 2016 at 11:36 AM, Zachary Turner via lldb-dev < lldb-dev@lists.llvm.org> wrote: > The thing is, the code is already full of data races. I think the > std::atomic is actually used incorrectly and is not even doing anything. > > That said, consider darwin on 32-bit, where I believe each stack frame is > 4-byte aligned. I dont' think there's any way the compiler can guarantee > that a function parameter is 8-byte aligned without allocating from the > heap, which is obviously impossible for a stack variable. > > On Fri, Aug 26, 2016 at 11:29 AM Greg Clayton <gclay...@apple.com> wrote: > >> >> > On Aug 26, 2016, at 11:24 AM, Greg Clayton via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> > >> >> >> >> On Aug 26, 2016, at 10:51 AM, Zachary Turner via lldb-dev < >> lldb-dev@lists.llvm.org> wrote: >> >> >> >> I recently updated to Visual Studio 2015 Update 3, which has improved >> its diagnostics. As a result of this, LLDB is uncompilable due to a slew >> of errors of the following nature: >> >> >> >> D:\src\llvm\tools\lldb\include\lldb/Target/Process.h(3256): error >> C2719: 'default_stop_addr': formal parameter with requested alignment of 8 >> won't be aligned >> >> >> >> The issue comes down to the fact that lldb::Address contains a >> std::atomic<uint64_t>, and is being passed by value pervasively throughout >> the codebase. There is no way to guarantee that this value is 8 byte >> aligned. This has always been a bug, but until now the compiler just >> hasn't been reporting it. >> >> >> >> Someone correct me if I'm wrong, but I believe this is a problem on >> any 32-bit platform, and MSVC is just the only one erroring. >> >> >> >> I'm not really sure what to do about this. Passing >> std::atomic<uint64>'s by value seems wrong to me. >> >> >> >> Looking at the code, I don't even know why it needs to be atomic. >> It's not even being used safely. We'll have a single function write the >> value and later read the value, even though it could have been used in the >> meantime. Maybe what is really intended is a mutex. Or maybe it doesn't >> need to be atomic in the first place. >> >> >> >> Does anyone have a suggestion on what to do about this? I'm currently >> blocked on this as I can't compile LLDB. >> > >> > Feel free to #ifdef around the m_offset member of Address and you can >> have the data race and compile. This seems like a compiler bug to me. If a >> struct/classe by value argument has alignment requirements, then the >> compiler should handle this correctly IMHO. Am I wrong???? >> >> Or if this isn't a compiler bug, feel free to modify anything that was >> passing Address by value and make it a "const Address &". > > > _______________________________________________ > lldb-dev mailing list > lldb-dev@lists.llvm.org > http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev > >
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