Am 17.01.2023 um 21:43 hat Stefan Hajnoczi geschrieben: > On Tue, 17 Jan 2023 at 12:17, Kevin Wolf <kw...@redhat.com> wrote: > > > > Am 17.01.2023 um 17:43 hat Warner Losh geschrieben: > > > On Tue, Jan 17, 2023 at 9:25 AM Kevin Wolf <kw...@redhat.com> wrote: > > > > > > > Am 17.01.2023 um 17:16 hat Warner Losh geschrieben: > > > > > On Tue, Jan 17, 2023 at 6:52 AM Emanuele Giuseppe Esposito < > > > > > eespo...@redhat.com> wrote: > > > > > > > > > > > QEMU does not compile when enabling clang's thread safety analysis > > > > > > (TSA), > > > > > > because some functions create wrappers for pthread mutexes but do > > > > > > not use any TSA macro. Therefore the compiler fails. > > > > > > > > > > > > In order to make the compiler happy and avoid adding all the > > > > > > necessary macros to all callers (lock functions should use > > > > > > TSA_ACQUIRE, while unlock TSA_RELEASE, and this applies to allusers > > > > > > of > > > > > > pthread_mutex_lock/pthread_mutex_unlock), > > > > > > simply use TSA_NO_TSA to supppress such warnings. > > > > > > > > > > I'm not sure I understand this quite right. Maybe a clarifying > > > > > question > > > > > will help me understand: Why is this needed for bsd-user but not > > > > > linux-user? How are they different here? > > > > > > > > FreeBSD's pthread headers include TSA annotations for some functions > > > > that force us to do something about them (for now: suppress the warnings > > > > in their callers) before we can enable -Wthread-safety for the purposes > > > > where we really want it. Without this, calling functions like > > > > pthread_mutex_lock() would cause compiler errors. > > > > > > > > glibc's headers don't contain such annotations, so the same is not > > > > necessary on Linux > > > > > > > > > > Thanks Kevin. With that explanation, these patches and their explanation > > > make perfect sense now. Often when there's a patch to bsd-user but not > > > linux-user, it's because bsd-user needs to do more in some way (which I > > > try > > > to keep up on). > > > > > > In this case, it's because FreeBSD's libc is a bit ahead of the curve. So > > > I > > > understand why it's needed, and what I need to do next (though I think > > > that > > > I may have to wait for the rest of qemu to be annotated)... > > > > I assume that the bsd-user part is actually sufficiently independent > > that you could do proper annotations there if you want. > > > > However, be aware that TSA has some serious limitations with C, so you > > can't express certain things, and it isn't as strict as it could be (in > > particular, function pointers bypass it). As long as you have global > > locks (as opposed to locks in structs), it kind of works, though. > > Certainly better than nothing. > > What are the limitations on locks in structs (a common case)?
TSA_GUARDED_BY() can't refer to a mutex in the same struct in C. You would have to have something like 'this', but it just doesn't exist. (I think in C++ you don't actually need 'this' because name resolution automatically starts at the struct or something - I neither know C++ well enough nor TSA with it, so take this with a grain of salt.) You can still annotate functions for such structs in C, because then you have a name for the struct, like this: void lock(Foo *foo) TSA_REQUIRES(foo->mutex); Kevin
