configure: Coerce gcc to use $LD instead of system default

The configure script will now try to coerce gcc to use the linker
pointed to by $LD instead of the system default (typically bfd ld).
Moreover, we now check for `ld.gold` and `ld.lld` before trying `ld`.

The previous behavior can be reverted to by using the new
--disable-ld-override flag.

On my machine gold seems to trigger an apparent infelicity in
constructor behavior, causing T5435_asm to fail. I've opened #13883 to
record this issue and have accepted the questionable constructor
ordering for the time being.

Test Plan: Validate with `config_args='--enable-ld-override'`

Reviewers: austin, hvr, simonmar

Subscribers: duog, nh2, rwbarton, thomie, erikd, snowleopard

GHC Trac Issues: #13541, #13810, #13883

Differential Revision: https://phabricator.haskell.org/D3449

1 files changed, 60 insertions, 46 deletions

diff --git a/aclocal.m4 b/aclocal.m4
index b94f70bada..677c0e77bc 100644
--- a/aclocal.m4
+++ b/aclocal.m4
@@ -590,7 +590,7 @@ AC_DEFUN([FP_SET_CFLAGS_C99],
 
 # FPTOOLS_SET_C_LD_FLAGS
 # ----------------------------------
-# Set the C, LD and CPP flags for a given platform
+# Set the C, LD and CPP flags for a given platform.
 # $1 is the platform
 # $2 is the name of the CC flags variable
 # $3 is the name of the linker flags variable when linking with gcc
@@ -598,7 +598,6 @@ AC_DEFUN([FP_SET_CFLAGS_C99],
 # $5 is the name of the CPP flags variable
 AC_DEFUN([FPTOOLS_SET_C_LD_FLAGS],
 [
-    FIND_LD([$$1],[UseLd])
     AC_MSG_CHECKING([Setting up $2, $3, $4 and $5])
     case $$1 in
     i386-*)
@@ -665,15 +664,6 @@ AC_DEFUN([FPTOOLS_SET_C_LD_FLAGS],
 
     esac
 
-    case $UseLd in
-         *ld.gold)
-         $3="$$3 -fuse-ld=gold"
-         ;;
-         *ld.bfd)
-         $3="$$3 -fuse-ld=bfd"
-         ;;
-    esac
-
     # If gcc knows about the stack protector, turn it off.
     # Otherwise the stack-smash handler gets triggered.
     echo 'int main(void) {return 0;}' > conftest.c
@@ -2015,41 +2005,6 @@ AC_DEFUN([FIND_LLVM_PROG],[
     fi
 ])
 
-# FIND_LD
-# ---------
-# Find the version of `ld` to use. This is used in both in the top level
-# configure.ac and in distrib/configure.ac.in.
-#
-# $1 = the platform
-# $2 = the variable to set
-#
-AC_DEFUN([FIND_LD],[
-    AC_CHECK_TARGET_TOOL([LD], [ld])
-    case $1 in
-        arm*linux*       | \
-        aarch64*linux*   )
-            # Arm and Aarch64 requires use of the binutils ld.gold linker.
-            # This case should catch at least arm-unknown-linux-gnueabihf,
-            # arm-linux-androideabi, arm64-unknown-linux and
-            # aarch64-linux-android
-            AC_CHECK_TARGET_TOOL([LD_GOLD], [ld.gold])
-            if test "$LD_GOLD" != ""; then
-                $2="$LD_GOLD"
-            elif test `$LD --version | grep -c "GNU gold"` -gt 0; then
-                AC_MSG_NOTICE([ld is ld.gold])
-                $2="$LD"
-            else
-                AC_MSG_WARN([could not find ld.gold, falling back to $LD])
-                $2="$LD"
-            fi
-            ;;
-        *)
-            $2="$LD"
-            ;;
-    esac
-    CHECK_LD_COPY_BUG($1)
-])
-
 # CHECK_LD_COPY_BUG()
 # -------------------
 # Check for binutils bug #16177 present in some versions of the bfd ld
@@ -2284,4 +2239,63 @@ AC_DEFUN([FP_BFD_SUPPORT], [
     )
 ])
 
+
+# FP_CC_LINKER_FLAG_TRY()
+# --------------------
+# Try a particular linker to see whether we can use it. In particular, determine
+# whether we can convince gcc to use it via a -fuse-ld=... flag.
+#
+# $1 = the name of the linker to try
+# $2 = the variable to set with the appropriate GHC flag if the linker is
+# found to be usable
+AC_DEFUN([FP_CC_LINKER_FLAG_TRY], [
+    AC_MSG_CHECKING([whether C compiler supports -fuse-ld=$1])
+    echo 'int main(void) {return 0;}' > conftest.c
+    if $CC -o conftest.o -fuse-ld=$1 conftest.c > /dev/null 2>&1
+    then
+        $2="-fuse-ld=$1"
+        AC_MSG_RESULT([yes])
+    else
+        AC_MSG_RESULT([no])
+    fi
+    rm -f conftest.c conftest.o
+])
+
+# FIND_LD
+# ---------
+# Find the version of `ld` to use and figure out how to get gcc to use it for
+# linking (if --enable-ld-override is enabled). This is used in both in the top
+# level configure.ac and in distrib/configure.ac.in.
+#
+# $1 = the platform
+# $2 = the variable to set with GHC options to configure gcc to use the chosen linker
+#
+AC_DEFUN([FIND_LD],[
+    AC_ARG_ENABLE(ld-override,
+      [AC_HELP_STRING([--disable-ld-override],
+        [Prevent GHC from overriding the default linker used by gcc. If ld-override is enabled GHC will try to tell gcc to use whichever linker is selected by the LD environment variable. [default=override enabled]])],
+      [],
+      [enable_ld_override=yes])
+
+    if test "x$enable_ld_override" = "xyes"; then
+        AC_CHECK_TARGET_TOOLS([LD], [ld.gold ld.lld ld])
+        UseLd=''
+
+        out=`$LD --version`
+        case $out in
+          "GNU ld"*)   FP_CC_LINKER_FLAG_TRY(bfd, $2) ;;
+          "GNU gold"*) FP_CC_LINKER_FLAG_TRY(gold, $2) ;;
+          "LLD"*)      FP_CC_LINKER_FLAG_TRY(lld, $2) ;;
+          *) AC_MSG_NOTICE([unknown linker version $out]) ;;
+        esac
+        if test "z$2" = "z"; then
+            AC_MSG_NOTICE([unable to convince '$CC' to use linker '$LD'])
+        fi
+   else
+        AC_CHECK_TARGET_TOOL([LD], [ld])
+   fi
+
+   CHECK_LD_COPY_BUG([$1])
+])
+
 # LocalWords:  fi