quantum added a comment. In D64537#1588699 <https://reviews.llvm.org/D64537#1588699>, @dschuff wrote:
> I had a reply that got eaten here, so I'm going to keep trolling you on your > CL since we don't have a design doc for this. > The `offset` field of a data segment initializer can be a `global.get` on an > imported global. > (https://webassembly.github.io/spec/core/valid/instructions.html#constant-expressions). > Since each thread is separately instantiated with separate JS, we could have > a global import like `__tls_base` which has a different value in each thread. > Then we wouldn't need to manually call the init code anywhere. Would there be > other advantages or disadvantages for that? I already answered this one: In D64537#1586614 <https://reviews.llvm.org/D64537#1586614>, @quantum wrote: > In D64537#1586556 <https://reviews.llvm.org/D64537#1586556>, @dschuff wrote: > > > The `offset` field of a segment can be a constant expression > > <https://webassembly.github.io/spec/core/valid/instructions.html#constant-expressions> > > which can be a `global.get` of an imported global. So we could have an > > imported global `__tls_base` which is different for each thread, and have > > an active segment with that as its segment offset? > > > I didn't know that it could have been a constant expression. I don't think > this would have worked very well on the main thread though, since we need to > run `malloc` before we can compute `__tls_base`. I think this requires the > global to be mutable, if only because we need to be able to initialize it on > the main thread. The problem I found with the import approach is that the main thread cannot use `global.get` of an imported global to get the location of TLS, mainly because it needs to be `malloc`'d. To use `malloc`, the main thread needs to be initialized. This will result in a circular dependency. Repository: rL LLVM CHANGES SINCE LAST ACTION https://reviews.llvm.org/D64537/new/ https://reviews.llvm.org/D64537 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
