I think malloc is something neither the asm.js nor wasm ctor evallers support currently (asm.js code looks like it allows using DYNAMICTOP_PTR, but if the value there changes, we fail to eval that ctor). In both cases, the tricky thing is to turn the malloc into a fully static allocation, which needs some care as the location of dynamically allocated memory is not always set at compile time (we allow static allocations during startup, like for the filesystem - this is something we could reconsider).
Re-ordering should work, yeah. In asm2wasm we currently just have the list of constructors, so we'd need to also preserve their priorities after LLVM, but that doesn't seem too hard. For the wasm backend, I believe they are all collapsed into a single ctor anyhow, so that model would need to change to allow such optimization. On Mon, Aug 20, 2018 at 5:58 PM Charles Vaughn <[email protected]> wrote: > Looking into why EVAL_CTORs isn't helping with my project, I've come > across a limitation that seems to only exist for WASM, not asm.js. Notably > some of the initializers in my project invoke malloc (I believe by way of > shared pointer initialization). It looks like malloc invokes sbrk (which is > explicitly disallowed by the asm.js ctor_evaller). In the case of binaryen > this fails by way of sbrk trying to access DYNAMICTOP_PTR, which ends up as > a '...stopping since could not eval: tried to access a dangerous > (import-initialized) global: global$0' > > It does seem like something that could be handled, and would be a big win > for more dynamic initialization type scenarios. I believe it works when > targetting asm.js as that handles its memory allocation differently. > > Another point is that constructor evaluation order is flexible. I know > there is some machinery to control initializer ordering, which may limit > this approach in cases where it does matter, but it's possible for the > constructor evaluator to re-order constructors so that eval-able ones are > moved to the front of the execution list. > > > -- > You received this message because you are subscribed to the Google Groups > "emscripten-discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "emscripten-discuss" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
