Patchwork [RFT,v2] configure: Simplify alternate .text segment

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Submitter Ed Maste
Date June 20, 2013, 1:15 p.m.
Message ID <1371734143-780-1-git-send-email-emaste@freebsd.org>
Download mbox | patch
Permalink /patch/252924/
State New
Headers show

Comments

Ed Maste - June 20, 2013, 1:15 p.m.
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 +++++---
Richard Henderson - June 21, 2013, 6:37 p.m.
On 06/20/2013 06:15 AM, Ed Maste wrote:
> +    try_ldflags="-Ttext-segment=$textseg_addr"

Two problems: (1) you forgot "-Wl," here.
(2) We're running into some strange problem with git submodule init dtc.

>From config.log:

> cc -Werror -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wold-style-declaration -Wold-style-definition -Wtype-limits -fstack-protector-all -I/usr/include/libpng15 -I/usr/include/spice-server -I/usr/include/cacard -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/nss3 -I/usr/include/nspr4 -I/usr/include/spice-1 -I/usr/include/nss3 -I/usr/include/nspr4 -pthread -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/pixman-1 -I$(SRC_PATH)/dtc/libfdt -o /tmp/qemu-conf-29328-15251-22199.exe /tmp/qemu-conf-7372-15251-10868.c -Wl,--warn-common -m64 -g -Wl,-Ttext-segment=0x60000000
> cc1: error: $(SRC_PATH)/dtc/libfdt: No such file or directory [-Werror]
> cc1: all warnings being treated as errors

And because of that -Werror, we never detect that -Ttext-segment is supported,
which leads to the incorrect frobbing of the config-host.ld:

>   PROVIDE (__executable_start = 0x60000000SEGMENT_START("text-segment", 0x400000)); . = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;

I have no idea what's going wrong with the libfdt thing...


r~

Patch

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