1 files changed, 39 insertions, 3 deletions

diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index 388e5464616..597e8105fa1 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@@ -17,9 +17,40 @@
 , isGNU ? false, isClang ? cc.isClang or false, gnugrep ? null
 , buildPackages ? {}
 , libcxx ? null
+
+# Whether or not to add `-B` and `-L` to `nix-support/cc-{c,ld}flags`
+, useCcForLibs ?
+
+  # Always add these flags for Clang, because in order to compile (most
+  # software) it needs libraries that are shipped and compiled with gcc.
+  if isClang then true
+
+  # Never add these flags for a build!=host cross-compiler or a host!=target
+  # ("cross-built-native") compiler; currently nixpkgs has a special build
+  # path for these (`crossStageStatic`).  Hopefully at some point that build
+  # path will be merged with this one and this conditional will be removed.
+  else if (with stdenvNoCC; buildPlatform != hostPlatform || hostPlatform != targetPlatform) then false
+
+  # Never add these flags when wrapping the bootstrapFiles' compiler; it has a
+  # /usr/-like layout with everything smashed into a single outpath, so it has
+  # no trouble finding its own libraries.
+  else if (cc.passthru.isFromBootstrapFiles or false) then false
+
+  # Add these flags when wrapping `xgcc` (the first compiler that nixpkgs builds)
+  else if (cc.passthru.isXgcc or false) then true
+
+  # Add these flags when wrapping `stdenv.cc`
+  else if (cc.stdenv.cc.cc.passthru.isXgcc or false) then true
+
+  # Do not add these flags in any other situation.  This is `false` mainly to
+  # prevent these flags from being added when wrapping *old* versions of gcc
+  # (e.g. `gcc6Stdenv`), since they will cause the old gcc to get `-B` and
+  # `-L` flags pointing at the new gcc's libstdc++ headers.  Example failure:
+  # https://hydra.nixos.org/build/213125495
+  else false
+
+# the derivation at which the `-B` and `-L` flags added by `useCcForLibs` will point
 , gccForLibs ? if useCcForLibs then cc else null
-# same as `gccForLibs`, but generalized beyond clang
-, useCcForLibs ? isClang
 }:
 
 with lib;
@@ -321,7 +352,7 @@ stdenv.mkDerivation {
                       && targetPlatform.isLinux
                       && !(stdenv.targetPlatform.useAndroidPrebuilt or false)
                       && !(stdenv.targetPlatform.useLLVM or false)
-                      && gccForLibs != null) ''
+                      && gccForLibs != null) (''
       echo "--gcc-toolchain=${gccForLibs}" >> $out/nix-support/cc-cflags
 
       # Pull in 'cc.out' target to get 'libstdc++fs.a'. It should be in
@@ -329,6 +360,11 @@ stdenv.mkDerivation {
       # TODO(trofi): remove once gcc is fixed to move libraries to .lib output.
       echo "-L${gccForLibs}/${optionalString (targetPlatform != hostPlatform) "/${targetPlatform.config}"}/lib" >> $out/nix-support/cc-ldflags
     ''
+    # this ensures that when clang passes -lgcc_s to lld (as it does
+    # when building e.g. firefox), lld is able to find libgcc_s.so
+    + lib.optionalString (gccForLibs?libgcc) ''
+      echo "-L${gccForLibs.libgcc}/lib" >> $out/nix-support/cc-ldflags
+    '')
 
     ##
     ## General libc support