[Qemu-devel] [RFT PATCH v2] configure: Simplify alternate .text segment

[Ed Maste <emaste@freebsd.org>]

For bsd-user and linux-user emulation modes QEMU needs to be linked at an
alternate .text segment address, so that it's out of the way of the guest
executable.  Instead of including modified linker scripts for each arch,
just set the address with -Ttext-segment if supported, or by using sed to
edit the default linker script.

Note that ldscripts/alpha.ld was already unused prior to this change, as
it was handled by the "default placement of the application is fine" case.

Signed-off-by: Ed Maste <emaste@freebsd.org>
---
Changes from v1:
 - Drop removal of ldscripts from the patch for now.  They remain unused
   with v2 and can be removed later, but this makes the patch smaller
   during review and testing.
 - Don't require knowledge of the default .text address, as suggested by
   Richard Henderson.
 - Use configure's existing compile_prog to test for acceptance of the
   linker flag rather than a hack that fails on current binutils versions.

 configure            |  37 +++++---
diff --git a/configure b/configure
index ad32f87..b3025df 100755
--- a/configure
+++ b/configure
@@ -4072,9 +4072,6 @@ if test "$gcov" = "yes" ; then
   echo "GCOV=$gcov_tool" >> $config_host_mak
 fi
 
-# generate list of library paths for linker script
-$ld --verbose -v 2> /dev/null | grep SEARCH_DIR > config-host.ld
-
 # use included Linux headers
 if test "$linux" = "yes" ; then
   mkdir -p linux-headers
@@ -4437,21 +4434,35 @@ if test "$gprof" = "yes" ; then
   fi
 fi
 
-if test "$ARCH" = "tci"; then
-  linker_script=""
-else
-  linker_script="-Wl,-T../config-host.ld -Wl,-T,\$(SRC_PATH)/ldscripts/\$(ARCH).ld"
-fi
-
 if test "$target_linux_user" = "yes" -o "$target_bsd_user" = "yes" ; then
+  textseg_addr=
   case "$ARCH" in
-  alpha | s390x | aarch64)
-    # The default placement of the application is fine.
+  arm | hppa | i386 | ia64 | m68k | ppc | ppc64 | s390 | sparc | sparc64 | x86_64)
+    textseg_addr=0x60000000
     ;;
-  *)
-    ldflags="$linker_script $ldflags"
+  mips)
+    textseg_addr=0x400000
     ;;
   esac
+  if [ -n "$textseg_addr" ]; then
+cat > $TMPC <<EOF
+int main(void) { return 0; }
+EOF
+    try_ldflags="-Ttext-segment=$textseg_addr"
+    if compile_prog "" "$try_ldflags"; then
+      ldflags="$ldflags $try_ldflags"
+    else
+      # In case ld does not support -Ttext-segment, edit the default linker
+      # script via sed to set the .text start addr.  This is needed on FreeBSD
+      # at least.
+      $ld --verbose | sed \
+        -e '1,/==================================================/d' \
+        -e '/==================================================/,$d' \
+        -e "s/[.] = [0-9a-fx]* [+] SIZEOF_HEADERS/. = $textseg_addr + SIZEOF_HEADERS/" \
+        -e "s/__executable_start = [0-9a-fx]*/__executable_start = $textseg_addr/" > config-host.ld
+      ldflags="$ldflags -Wl,-T../config-host.ld"
+    fi
+  fi
 fi
 
 echo "LDFLAGS+=$ldflags" >> $config_target_mak