Re: [PATCH] configure: Use lld --image-base for --disable-pie user mode binaries

[Fangrui Song <i@maskray.me>]

On 2019-11-15, Fangrui Song wrote:
>For lld, --image-base is the preferred way to set the base address.
>lld does not actually implement -Ttext-segment, but treats it as an alias for
>-Ttext. -Ttext-segment=0x60000000 combined with --no-rosegment can
>create a 1.6GB executable.
>
>Fix the problem by using --image-base for lld. GNU ld and gold will
>still get -Ttext-segment. Also delete the ld --verbose fallback introduced
>in 2013, which is no longer relevant or correct (the default linker
>script has changed).
>
>Signed-off-by: Fangrui Song <i@maskray.me>
>---
>  configure | 33 ++++++++++++---------------------
>  1 file changed, 12 insertions(+), 21 deletions(-)
>
>diff --git a/configure b/configure
>index 6099be1d84..2d45af0d09 100755
>--- a/configure
>+++ b/configure
>@@ -6336,43 +6336,34 @@ fi
>
>  # Probe for the need for relocating the user-only binary.
>  if ( [ "$linux_user" = yes ] || [ "$bsd_user" = yes ] ) && [ "$pie" = no ]; then
>-  textseg_addr=
>+  image_base=
>    case "$cpu" in
>      arm | i386 | ppc* | s390* | sparc* | x86_64 | x32)
>-      # ??? Rationale for choosing this address
>-      textseg_addr=0x60000000
>+      # An arbitrary address that makes it unlikely to collide with user
>+      # programs.
>+      image_base=0x60000000
>        ;;
>      mips)
>        # A 256M aligned address, high in the address space, with enough
>        # room for the code_gen_buffer above it before the stack.
>-      textseg_addr=0x60000000
>+      image_base=0x60000000
>        ;;
>    esac
>-  if [ -n "$textseg_addr" ]; then
>+  if [ -n "$image_base" ]; 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.
>-      if ! $ld --verbose >/dev/null 2>&1; then
>+    image_base_ldflags="-Wl,--image-base=$image_base"
>+    if ! compile_prog "" "$image_base_ldflags"; then
>+      image_base_ldflags="-Wl,-Ttext-segment=$image_base"
>+      if ! compile_prog "" "$image_base_ldflags"; then
>          error_exit \
>              "We need to link the QEMU user mode binaries at a" \
>              "specific text address. Unfortunately your linker" \
>-            "doesn't support either the -Ttext-segment option or" \
>-            "printing the default linker script with --verbose." \
>+            "supports neither --image-base nor -Ttext-segment. " \
>              "If you don't want the user mode binaries, pass the" \
>              "--disable-user option to configure."
>        fi
>-
>-      $ld --verbose | sed \
>-        -e '1,/==================================================/d' \
>-        -e '/==================================================/,$d' \
>-        -e "s/[.] = [0-9a-fx]* [+] SIZEOF_HEADERS/. = $textseg_addr + SIZEOF_HEADERS/" \
>-        -e "s/__executable_start = [0-9a-fx]*/__executable_start = $textseg_addr/" > config-host.ld
>-      textseg_ldflags="-Wl,-T../config-host.ld"
>      fi
>    fi
>  fi
>@@ -7945,7 +7936,7 @@ if test "$gprof" = "yes" ; then
>  fi
>
>  if test "$target_linux_user" = "yes" || test "$target_bsd_user" = "yes" ; then
>-  ldflags="$ldflags $textseg_ldflags"
>+  ldflags="$ldflags $image_base_ldflags"
>  fi
>
>  # Newer kernels on s390 check for an S390_PGSTE program header and
>-- 
>2.24.0
>

Ping :)