#7097: linker fails to load package with binding to foreign library ----------------------------------+----------------------------------------- Reporter: nus | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Runtime System | Version: 7.4.2 Keywords: | Os: Windows Architecture: x86 | Failure: None/Unknown Difficulty: Unknown | Testcase: Blockedby: 3658 | Blocking: Related: #2283 #3242 #1883 | ----------------------------------+----------------------------------------- Comment(by awson): I'd want to clarify things a bit here. Suppose we have some compiled dll exporting some function `foo`. Suppose we write a client program in C calling this `foo`. Regardless of how this `foo` is prototyped: as bare `foo` or as {{{__declspec(dllimport) foo}}} a client program will happily call it, but depending on a prototype in ''different ways'': in the first case this will be {{{call foo}}} and if this symbol is external a linker will generate a thunk for this `foo` as {{{jmp __imp_foo}}}, in the second case a C compiler always generates {{{call __imp_foo}}}. Thus the single thing matters here: '''which prototype of a function''' was visible to C compiler when it compiled a code calling that function. If that prototype had {{{__declspec(dllimport)}}} attribute attached, a C compiler generated a call against {{{__imp_foo}}}, otherwise - a call against bare {{{foo}}}. GHC FFI of modern era (with no C backend) always generates the second variant AFAIK. This also explains the difference between 32 and 64 GHCs for Windows. 64-bit GHC is distributed with mingw-w64 headers which use {{{__declspec(dllimport)}}} extensively, and many packages fail to compile. 32-bit GHC is distributed with mingw headers which has almost (or entirely?) no {{{__declspec(dllimport)}}} declared APIs. To make 64-bit GHC usable on Windows I manually removed all {{{__declspec(dllimport)}}} from mingw-w64 headers and now it all works smoothly. Hope this helps. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7097#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler