The runtime linker seems to be re-exporting some of the symbols of `libmingwex` from the rts archive (using `SymI_HasProto`). Only a very small subset of symbols are re-exporting. If a symbol is needed that isn't re-exported (e.g. `log1p`) then this code can't be run in GHCi because it will result in a duplicate symbols error. ### A workaround The `rts` seems to be a special case again. The linker seems to ignore the `extra-libraries` from the `package.conf`, which explains why you can put anything you want in there and it'll still compile. ``` 128 emptyPLS :: DynFlags -> PersistentLinkerState 129 emptyPLS _ = PersistentLinkerState { 130 closure_env = emptyNameEnv, 131 itbl_env = emptyNameEnv, 132 pkgs_loaded = init_pkgs, 133 bcos_loaded = [], 134 objs_loaded = [], 135 temp_sos = [] } 136 137 -- Packages that don't need loading, because the compiler 138 -- shares them with the interpreted program. 139 -- 140 -- The linker's symbol table is populated with RTS symbols using an 141 -- explicit list. See rts/Linker.c for details. 142 where init_pkgs = [rtsUnitId] ``` I've tried 2 approaches which haven't worked completely: 1. I tried removing the symbols from the export list and adding `libmingwex` to the rts's `package.conf`and have it just link against it. But turns out the `rts`'s `package.conf` is ignored on all platforms. I didn't want to have to make an exception for Windows here and I don't know why the other platforms also ignore it so I abandoned this approach. 1. I tried marking the symbols we're re-exporting as weak symbols, so there wouldn't be a change to existing code and would allow you to link against `libmingwex`. But unfortunately because of when the other libraries specified by `-l` are linked in, some of the symbols have already been used and thus aren't weak anymore. So I still get duplicate link errors. What I want to try now is leaving them as weak symbols, but loading `libmingwex.a` at `rts` initialization time. Much like how `kernel32` is loaded. This is hopefully early enough that the symbols haven't been used yet. ### Example ```hs -- LogFloat.hs module Main (main) where import Data.Number.LogFloat (log1p) main :: IO () main = print $ log1p 1.0 ``` `runGhc LogFloat.hs` will fail: ``` Loading package logfloat-0.13.3.3 ... linking ... LogFloat.hs: ...\x86_64-windows-ghc-7.11.20151123\logfloat-0.13.3.3-4JZYNCXKwghOD60rvMUAcn\HSlogfloat-0.13.3.3-4JZYNCXKwghOD60rvMUAcn.o: unknown symbol `log1p' LogFloat.hs: LogFloat.hs: unable to load package `logfloat-0.13.3.3' ```