mingw: Enable high-entropy ASLR on 64-bit Windows

To fully utilize HEASLR the image base address must also be set above
4 GiB. For consistency use the same address as MSVC uses by default.

This requires binutils 2.25 which isn't available on all common
distributions, so only enable it after checking that it's supported.

diff --git a/configure b/configure
index 09643db035ef4394acd193cc675e64cfc6f9eed3..0d40a927f071091623ff2ebb48abb0a0aec05b57 100755 (executable)
--- a/configure
+++ b/configure
@@ -693,10 +693,15 @@ case $host_cpu in
             fi
         elif [ "$SYS" = WINDOWS -o "$SYS" = CYGWIN ]; then
             ASFLAGS="$ASFLAGS -f win64"
-            # only the GNU toolchain is inconsistent in prefixing function names with _
-            [ $compiler = GNU ] && cc_check "" "-S" && grep -q "_main:" conftest && ASFLAGS="$ASFLAGS -DPREFIX"
-            [ $compiler = GNU ] && LDFLAGS="$LDFLAGS -Wl,--dynamicbase,--nxcompat,--tsaware"
-            [ $compiler = GNU ] && RCFLAGS="--target=pe-x86-64 $RCFLAGS"
+            if [ $compiler = GNU ]; then
+                # only the GNU toolchain is inconsistent in prefixing function names with _
+                cc_check "" "-S" && grep -q "_main:" conftest && ASFLAGS="$ASFLAGS -DPREFIX"
+                cc_check "" "-Wl,--high-entropy-va" && LDFLAGS="$LDFLAGS -Wl,--high-entropy-va"
+                LDFLAGS="$LDFLAGS -Wl,--dynamicbase,--nxcompat,--tsaware"
+                LDFLAGSCLI="$LDFLAGSCLI -Wl,--image-base,0x140000000"
+                SOFLAGS="$SOFLAGS -Wl,--image-base,0x180000000"
+                RCFLAGS="--target=pe-x86-64 $RCFLAGS"
+            fi
         else
             ASFLAGS="$ASFLAGS -f elf64"
         fi
@@ -1389,7 +1394,7 @@ if [ "$shared" = "yes" ]; then
             grep "extern.*x264" ${SRCPATH}/x264.h | sed -e "s/.*\(x264\w*\)\W.*/\1 DATA/;" >> x264.def
         else
             echo 'IMPLIBNAME=libx264.dll.a' >> config.mak
-            echo "SOFLAGS=-shared -Wl,--out-implib,\$(IMPLIBNAME) -Wl,--enable-auto-image-base $SOFLAGS" >> config.mak
+            echo "SOFLAGS=-shared -Wl,--out-implib,\$(IMPLIBNAME) $SOFLAGS" >> config.mak
         fi
     elif [ "$SYS" = "MACOSX" ]; then
         echo "SOSUFFIX=dylib" >> config.mak