fix: don't use fast-llvm for aarch32 (#555)

* fix: don't use fast-llvm for aarch32

fast-llvm bypasses the GHC LLVM mangler and the GNU assembler. The latter is currently required when using the gold linker for valid relocation sections.

* feat: remove usage of the fast-llvm flag

The fast-llvm flag was intented to avoid potential incompatibilities between LLVM and the assembler/linker toolchain by making LLVM responsible for machine-code generation.

It bypasses necessary code transformation and prevents valid program generation in some cases (e.g. cross-compilation to armv6l). It is planned for removal from GHC.

References:
https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3120

Co-authored-by: Michivi <[email protected]>

Author: michivi

builder/comp-builder.nix

@@ -75,9 +75,8 @@ let
       [ "--with-gcc=${stdenv.cc.targetPrefix}cc"
       ] ++
       # BINTOOLS
-      (if stdenv.hostPlatform.isLinux && !stdenv.targetPlatform.isAarch32
+      (if stdenv.hostPlatform.isLinux
         # use gold as the linker on linux to improve link times
-        # Causes segfaults on Aarch32 though.
         then [
           "--with-ld=${stdenv.cc.bintools.targetPrefix}ld.gold"
           "--ghc-option=-optl-fuse-ld=gold"

compiler/ghc/default.nix

@@ -98,9 +98,6 @@ let
     GhcRtsHcOpts += -fPIC
   '' + stdenv.lib.optionalString targetPlatform.useAndroidPrebuilt ''
     EXTRA_CC_OPTS += -std=gnu99
-  '' + stdenv.lib.optionalString useLLVM ''
-    GhcStage2HcOpts += -fast-llvm
-    GhcLibHcOpts += -fast-llvm
   '' + stdenv.lib.optionalString (!enableTerminfo) ''
     WITH_TERMINFO=NO
   ''
@@ -214,13 +211,11 @@ in let configured-src = stdenv.mkDerivation (rec {
             "--enable-bootstrap-with-devel-snapshot"
         ] ++ stdenv.lib.optionals (disableLargeAddressSpace) [
             "--disable-large-address-space"
-        ];
-        # FIXME Currently causes segfaults on armv6l cross-compilation.
-        # ++ stdenv.lib.optionals (targetPlatform.isAarch32) [
-        #     "CFLAGS=-fuse-ld=gold"
-        #     "CONF_GCC_LINKER_OPTS_STAGE1=-fuse-ld=gold"
-        #     "CONF_GCC_LINKER_OPTS_STAGE2=-fuse-ld=gold"
-        # ] ;
+        ] ++ stdenv.lib.optionals (targetPlatform.isAarch32) [
+            "CFLAGS=-fuse-ld=gold"
+            "CONF_GCC_LINKER_OPTS_STAGE1=-fuse-ld=gold"
+            "CONF_GCC_LINKER_OPTS_STAGE2=-fuse-ld=gold"
+        ] ;
 
         outputs = [ "out" ];
         phases = [ "unpackPhase" "patchPhase" ]