Hi Tamar,
I think the difficulty here is more with dynamic *outputs* rather than dynamic inputs/dependencies.
We do not statically know which of the following three alternatives holds:
* `*.dyn_o/hi` files are not built at all.
* `*.dyn_o/hi` files are built via a separate execution of GHC.
* `*.dyn_o/hi` files are built together with `*.o/hi` files, in a single execution of GHC with `-dynamic-too`.
Here is the current implementation:
https://gitlab.haskell.org/ghc/ghc/blob/master/hadrian/src/Rules/Compile.hs#...
I believe the last person looking into this was James Foster, so CC-ing to him in case he has any insights.
Cheers,
Andrey
________________________________
From: Phyx
The Make build system happens to do the right thing, somehow. I believe we should be able to express the same logic in Shake, but it's not easy.
I believe this typically works because GCC and GHC support dumping the dependencies that a command would have caused to a file. So your dynamic dependencies don't matter as their static to the build system after this invocation.
See
https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/separate_com...
These Compilers are able to dump out make rules which enabled better dependency handling..
Kind regards,
Tamar
Sent from my Mobile
On Tue, Dec 10, 2019, 00:58 Andrey Mokhov
Ugh. That's not a very happy state of affairs, is it? It didn't happen with 'make'.
Is it a fundamental problem, or just not yet fixed?
I think this is not a fundamental problem, but the problem of getting dependencies right. In this case, the complexity comes from the fact that a single invocation of GHC produces a set of files, and which set depends on the command line flags, which are in turn determined dynamically by reading environment settings (specifically, `platformSupportsSharedLibs`). Such rules are hard to describe precisely, because build systems are tuned to the typical case where we statically know, for every output file, which rule produces it -- recall the Tasks = k -> Maybe Task function from our paper. In this case, we deal with something like k -> f (Maybe Task) instead, i.e. with `f` around the Maybe. The Make build system happens to do the right thing, somehow. I believe we should be able to express the same logic in Shake, but it's not easy. (I never really had a chance to look at dynamic builds, since they are not supported on Windows. I guess I should finally find a Linux box for Hadrian.) Cheers, Andrey _______________________________________________ ghc-devs mailing list ghc-devs@haskell.orgmailto:ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs