bintools-wrapper: default platform versions for darwin

Instead of always supplying flags, apply the flags as defaults. Use
clang's native flags instead of lifting the linker flags from binutils
with `-Wl,`.

If a project is using clang to drive linking, make clang do the right
thing with MACOSX_DEPLOYMENT_TARGET. This can be overridden by command
line arguments. This will cause modern clang to pass
`-platform_version 10.12 0.0.0`, since it doesn't know about the SDK
settings. Older versions of clang will pass down `-macos_version_min`
flags with no sdk version.

At the linker layer, apply a default value for anything left
ambiguous. If nothing is specified, pass a full
`-platform_version`. If only `-macos_version_min` is specified, then
lock down the sdk_version explicitly with `-sdk_version`. If a min
version and sdk version is passed, do nothing.

pkgs/build-support/bintools-wrapper/add-darwin-ldflags-before.sh

@@ -0,0 +1,70 @@
+# Unconditionally adding in platform version flags will result in warnings that
+# will be treated as errors by some packages. Add any missing flags here.
+
+# There are two things to be configured: the "platform version" (oldest
+# supported version of macos, ios, etc), and the "sdk version".
+#
+# The modern way of configuring these is to use:
+#    -platform_version $platform $platform_version $sdk_version"
+#
+# The old way is still supported, and uses flags like:
+#    -${platform}_version_min $platform_version
+#    -sdk_version $sdk_version
+#
+# If both styles are specified ld will combine them. If multiple versions are
+# specified for the same platform, ld will emit an error.
+#
+# The following adds flags for whichever properties have not already been
+# provided.
+
+havePlatformVersionFlag=
+haveDarwinSDKVersion=
+haveDarwinPlatformVersion=
+
+n=0
+nParams=${#params[@]}
+while (( n < nParams )); do
+    p=${params[n]}
+    case "$p" in
+        # the current platform
+        -@darwinPlatform@_version_min)
+            haveDarwinPlatformVersion=1
+            ;;
+
+        # legacy aliases
+        -macosx_version_min|-iphoneos_version_min|-iosmac_version_min|-uikitformac_version_min)
+            haveDarwinPlatformVersion=1
+            ;;
+
+        -sdk_version)
+            haveDarwinSDKVersion=1
+            ;;
+
+        -platform_version)
+            havePlatformVersionFlag=1
+
+            # If clang can't determine the sdk version it will pass 0.0.0. This
+            # has runtime effects so we override this to use the known sdk
+            # version.
+            if [ "${params[n+3]-}" = 0.0.0 ]; then
+                params[n+3]=@darwinSdkVersion@
+            fi
+            ;;
+    esac
+    n=$((n + 1))
+done
+
+# If the caller has set -platform_version, trust they're doing the right thing.
+# This will be the typical case for clang in nixpkgs.
+if [ ! "$havePlatformVersionFlag" ]; then
+    if [ ! "$haveDarwinSDKVersion" ] && [ ! "$haveDarwinPlatformVersion" ]; then
+        # Nothing provided. Use the modern "-platform_version" to set both.
+        extraBefore+=(-platform_version @darwinPlatform@ @darwinMinVersion@ @darwinSdkVersion@)
+    elif [ ! "$haveDarwinSDKVersion" ]; then
+        # Add missing sdk version
+        extraBefore+=(-sdk_version @darwinSdkVersion@)
+    elif [ ! "$haveDarwinPlatformVersion" ]; then
+        # Add missing platform version
+        extraBefore+=(-@darwinPlatform@_version_min @darwinMinVersion@)
+    fi
+fi

pkgs/build-support/bintools-wrapper/default.nix

@@ -252,11 +252,6 @@ stdenv.mkDerivation {
       fi
     '')
 
-    # Ensure consistent LC_VERSION_MIN_MACOSX and remove LC_UUID.
-    + optionalString stdenv.targetPlatform.isMacOS ''
-      echo "-sdk_version 10.12 -no_uuid" >> $out/nix-support/libc-ldflags-before
-    ''
-
     ##
     ## User env support
     ##
@@ -310,6 +305,13 @@ stdenv.mkDerivation {
       echo "-arch ${targetPlatform.darwinArch}" >> $out/nix-support/libc-ldflags
     ''
 
+    ###
+    ### Remove LC_UUID
+    ###
+    + optionalString (stdenv.targetPlatform.isDarwin && !(stdenv.cc.bintools.bintools.isGNU or false)) ''
+      echo "-no_uuid" >> $out/nix-support/libc-ldflags-before
+    ''
+
     + ''
       for flags in "$out/nix-support"/*flags*; do
         substituteInPlace "$flags" --replace $'\n' ' '
@@ -320,6 +322,20 @@ stdenv.mkDerivation {
       substituteAll ${../wrapper-common/utils.bash} $out/nix-support/utils.bash
     ''
 
+    ###
+    ### Ensure consistent LC_VERSION_MIN_MACOSX
+    ###
+    + optionalString stdenv.targetPlatform.isDarwin (
+      let
+        inherit (stdenv.targetPlatform) darwinMinVersion darwinPlatform darwinSdkVersion;
+      in ''
+        export darwinPlatform=${darwinPlatform}
+        export darwinMinVersion=${darwinMinVersion}
+        export darwinSdkVersion=${darwinSdkVersion}
+        substituteAll ${./add-darwin-ldflags-before.sh} $out/nix-support/add-local-ldflags-before.sh
+      ''
+    )
+
     ##
     ## Extra custom steps
     ##

pkgs/build-support/bintools-wrapper/ld-wrapper.sh

@@ -78,6 +78,14 @@ fi
 
 extraAfter+=($NIX_LDFLAGS_AFTER_@suffixSalt@)
 
+# These flags *must not* be pulled up to -Wl, flags, so they can't go in
+# add-flags.sh. They must always be set, so must not be disabled by
+# NIX_LDFLAGS_SET.
+if [ -e @out@/nix-support/add-local-ldflags-before.sh ]; then
+    source @out@/nix-support/add-local-ldflags-before.sh
+fi
+
+
 # Specify the target emulation if nothing is passed in ("-m" overrides this
 # environment variable). Ensures we never blindly fallback on targeting the host
 # platform.

pkgs/development/tools/misc/binutils/default.nix

@@ -143,6 +143,7 @@ stdenv.mkDerivation {
 
   passthru = {
     inherit targetPrefix;
+    isGNU = true;
   };
 
   meta = with lib; {