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)? Stefan
