Commit 60c26403 authored by Committed by Marge Bot
linker: Move -optl flags to end of linker invocation.
Until now, giving `-optl` linker flags to `ghc` on the command line placed them in the wrong place in the `ld` command line: They were given before all the Haskell libararies, when they should appear after. Background: Most linkers like `ld.bfd` and `ld.gold`, but not the newer LLVM `lld`, work in a way where the order of `-l` flags given matters; earlier `-lmylib1` flags are supposed to create "holes" for linker symbols that are to be filled with later `lmylib2` flags that "fill the holes" for these symbols. As discovered in https://github.com/haskell/cabal/pull/5451#issuecomment-518001240, the `-optl` flags appeared before e.g. the -lHStext-220.127.116.11 -lHSbinary-0.8.6.0 -lHScontainers-0.6.0.1 flags that GHC added at the very end. Haskell libraries typically depend on C libraries, so `-lHS*` flags will create holes for the C libraries to fill in, but that only works when those libraries' `-l` flags are given **after** the `-lHS*` flags; until now they were given before, which was wrong. This meant that Cabal's `--ld-options` flag and `ld-options` `.cabal` file field were pretty ineffective, unless you used the `--ld-option=--start-group` hack as (https://github.com/haskell/cabal/pull/5451#issuecomment-406761676) that convinces the classical linkers to not be dependent on the order of linker flags given. This commit fixes the problem by simply flipping the order, putting `-optl` flags at the end, after Haskell libraries. The code change is effectively only `args1 ++ args` -> `args ++ args1` but the commit also renames the variables for improved clarity. Simple way to test it: ghc --make Main.hs -fforce-recomp -v -optl-s on a `Main.hs` like: import qualified Data.Set as Set main = print $ Set.fromList "hello"
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