[Qemu-devel] [PATCH v3] configure: Simplify alternate .text segment

[Richard Henderson <rth@twiddle.net>]

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.

Cc: Ed Maste <emaste@freebsd.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 configure | 48 +++++++++++++++++++++++++++++++-----------------
 2 files changed, 31 insertions(+), 18 deletions(-)
--

Changes v2-v3:
  * Move the check for textseg_ldflags much earlier in the configure file,
    so that we've not got cflags invalid for configure time.  Plus, the
    check (and generated ld script) only gets done once, not once per
    target directory.
  * Remove ia64 from the hosts that get relocation
  * Handle s390x like s390.

Tested on x86_64, arm, hppa (old binutils needing config-host.ld),
sparc64, and ia64.  All various versions of linux.


r~



diff --git a/configure b/configure
index ad32f87..63da418 100755
--- a/configure
+++ b/configure
@@ -3444,6 +3444,36 @@ if test "$cpu" = "s390x" ; then
   roms="$roms s390-ccw"
 fi
 
+# Probe for the need for relocating the user-only binary.
+if test "$pie" = "no" ; then
+  textseg_addr=
+  case "$cpu" in
+    arm | hppa | i386 | m68k | ppc | ppc64 | s390* | sparc | sparc64 | x86_64)
+      textseg_addr=0x60000000
+      ;;
+    mips)
+      textseg_addr=0x400000
+      ;;
+  esac
+  if [ -n "$textseg_addr" ]; then
+    cat > $TMPC <<EOF
+    int main(void) { return 0; }
+EOF
+    textseg_ldflags="-Wl,-Ttext-segment=$textseg_addr"
+    if ! compile_prog "" "$textseg_ldflags"; then
+      # 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 = $textseg_addr/" > config-host.ld
+      textseg_ldflags="-Wl,-T../config-host.ld"
+    fi
+  fi
+fi
+
 # add pixman flags after all config tests are done
 QEMU_CFLAGS="$QEMU_CFLAGS $pixman_cflags $fdt_cflags"
 libs_softmmu="$libs_softmmu $pixman_libs"
@@ -4072,9 +4102,6 @@ if test "$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 +4464,8 @@ 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 "$target_bsd_user" = "yes" ; then
-  case "$ARCH" in
-  alpha | s390x | aarch64)
-    # The default placement of the application is fine.
-    ;;
-  *)
-    ldflags="$linker_script $ldflags"
-    ;;
-  esac
+  ldflags="$ldflags $textseg_ldflags"
 fi
 
 echo "LDFLAGS+=$ldflags" >> $config_target_mak