#10531: modules that can be linked successfully when compiled with optimizations, fail to link with: multiple definition of `__stginit_ZCMain' -------------------------------------+------------------------------------- Reporter: imz | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: attached Blocked By: | Blocking: Related Tickets: #437 | Differential Revisions: -------------------------------------+------------------------------------- Changes (by rwbarton): * related: 437 => #437 Comment: So the problem here is that while the interface file contains a hash of flags like `-main-is`, that hash isn't incorporated into the top-level interface hash. When you remove `A.o` (but ''not'' `A.hi`) and then rebuild `a`, GHC builds a new `A.o` with the symbols like `ZCMain_main_info` but doesn't update the interface file `A.hi` on disk accordingly, because it thinks it hasn't changed (the interface hash didn't change because it doesn't include the flag hash). Then when building `b` GHC sees that the interface file claims that main was not A.main when A was built, so GHC sees no need to recompile A. Relevant code starts at https://github.com/ghc/ghc/blob/bac927b9770ff769128b66d13a3e72bf5a9bc514/com.... This looks like an easy fix except there are a few comments there I don't understand, like the one about two hashes being returned for the flag hash and the one that claims that the ABI hash depends on "flag abi hash". (Perhaps they apply to a version of the patch for #437 from before it was committed?) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10531#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler