Re: [libvirt] [PATCH 1/2] Simplify RELRO_LDFLAGS
On Tue, Aug 20, 2013 at 01:23:18PM -0600, Eric Blake wrote:
On 08/20/2013 08:39 AM, Guido Günther wrote:
> by adding it to AM_LDFLAGS instead of every linking rule and
> by avoiding a forked grep.
> ---
> Daniel kind of nacked the AM_LDFLAGS part already but I think it's a
> reasonable cleanup. We should rather use AM_LDFLAGS everywhere which
> (we currently don't and which would be another cleanup). Or are there
> any reasons to not have a read only GOT?
Personally, I like the idea of using AM_LDFLAGS everywhere, but as
Daniel and I have opposing opinions, we'll need a third person to speak up.
O.k. I think we lose more by not having eqaul AM_LDFLAGS everywhere
since there are already several places that did lack some flags since
it's error prone to maintain all locations correctly.
> +++ b/m4/virt-linker-relro.m4
> @@ -22,10 +22,10 @@ AC_DEFUN([LIBVIRT_LINKER_RELRO],[
> AC_MSG_CHECKING([for how to force completely read-only GOT table])
>
> RELRO_LDFLAGS=
> - `$LD --help 2>&1 | grep -- "-z relro" >/dev/null`
&& \
> - RELRO_LDFLAGS="-Wl,-z -Wl,relro"
> - `$LD --help 2>&1 | grep -- "-z now" >/dev/null` &&
\
> - RELRO_LDFLAGS="$RELRO_LDFLAGS -Wl,-z -Wl,now"
> + case `$LD --help 2>&1` in
> + *"-z relro"*) RELRO_LDFLAGS="-Wl,-z -Wl,relro" ;&
';&' is a bashism; it is not portable to configure scripts
> + *"-z now"*) RELRO_LDFLAGS="$RELRO_LDFLAGS -Wl,-z
-Wl,now" ;;
> + esac
Instead, this needs to be:
ld_help=`$LD --help 2>&1`
case $ld_help in
*"-z relro"*) RELRO_LDFLAGS="-Wl,-z -Wl,relro" ;;
esac
case $ld_help in
*"-z now"*) RELRO_LDFLAGS="$RELRO_LDFLAGS -Wl,-z -Wl,now" ;;
esac
> @@ -1812,7 +1814,6 @@ libvirt_la_LDFLAGS = \
> -version-info $(LIBVIRT_VERSION_INFO) \
> $(LIBVIRT_NODELETE) \
> $(AM_LDFLAGS) \
> - $(RELRO_LDFLAGS) \
> $(CYGWIN_EXTRA_LDFLAGS) \
> $(MINGW_EXTRA_LDFLAGS) \
> $(NULL)
Hmm - maybe I see why Daniel expressed his opinion for not using
$(AM_LDFLAGS) - notice that libraries to NOT use $(PIE_LDFLAGS)...
> @@ -1964,7 +1963,6 @@ virtlockd_CFLAGS = \
> virtlockd_LDFLAGS = \
> $(AM_LDFLAGS) \
> $(PIE_LDFLAGS) \
> - $(RELRO_LDFLAGS) \
> $(CYGWIN_EXTRA_LDFLAGS) \
> $(MINGW_EXTRA_LDFLAGS) \
> $(NULL)
...but executables do. But even then, maybe we want:
LIBRARY_LDFLAGS = $(AM_LDFLAGS)
EXEC_LDFLAGS = $(AM_LDFLAGS) $(PIE_LDFLAGS)
That would be fine with me but I'd do this as a separate cleanup since
AM_LDFLAGS currently only carries flags suitable for both lib and
executable builds.
Cheers,
-- Guido
then use the appropriate $({LIBRARY,EXEC}_LDFLAGS) in each place,
rather
than having lots of duplicate $(PIE_LDFLAGS)?
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org