[PATCH v2] configure: Use lld --image-base for --disable-pie user mode binaries

[Fangrui Song]

On 2019-11-27, Alex Bennée wrote:
> Fangrui Song <address@hidden> writes:
>
> > 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 <address@hidden>
>
> This patch no longer applies cleanly to configure so I couldn't test it.

configure was touched twice last week, but git still works.
Anyway, I am uploading a new patch without In-Reply-To.

> > ---
> >   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
>
> The comment probably belongs up above when we define the empty variable
> unless it really is specifically about these targets.

Moved the comment.

> Renaming textseg_addr seems like unnecessary churn for this patch.

Renaming is necessary. "Text segment" is no more an appropriate term
even with GNU ld due to the prevalence of -z separate-code
(--enable-separate-code is the default on Linux x86-64 in recent
binutils releases). There is a PF_R PT_LOAD before PF_R|PF_X PT_LOAD
(text segment). One may argue that we can name the two PT_LOAD
collectively as "text segment but I don't think that is appropriate.

> >         ;;
> >       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

(I'm not subscribed to the list, so please CC me.
I made this reply by downloading
https://lists.gnu.org/archive/mbox/qemu-devel/2019-11)

qemu-image-base.patch
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