Re: [PATCH] Check alignment of PT_LOAD segment only if possible

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 10/12/2021 17:59, H.J. Lu wrote:
> Add a configure check for 2MB variable alignment and check alignment of
> PT_LOAD segment only if 2MB variable alignment is supported.
> 
> Tested with cross build to glibcs-alpha-linux-gnu.
> ---
>  configure    | 40 +++++++++++++++++++++++++++++++++++++++-
>  configure.ac | 11 +++++++++++
>  elf/Makefile | 15 ++++++++++-----
>  3 files changed, 60 insertions(+), 6 deletions(-)
> 
> diff --git a/configure b/configure
> index e4d013907c..9da30f428f 100755
> --- a/configure
> +++ b/configure
> @@ -732,6 +732,7 @@ infodir
>  docdir
>  oldincludedir
>  includedir
> +runstatedir
>  localstatedir
>  sharedstatedir
>  sysconfdir
> @@ -845,6 +846,7 @@ datadir='${datarootdir}'
>  sysconfdir='${prefix}/etc'
>  sharedstatedir='${prefix}/com'
>  localstatedir='${prefix}/var'
> +runstatedir='${localstatedir}/run'
>  includedir='${prefix}/include'
>  oldincludedir='/usr/include'
>  docdir='${datarootdir}/doc/${PACKAGE_TARNAME}'
> @@ -1097,6 +1099,15 @@ do
>    | -silent | --silent | --silen | --sile | --sil)
>      silent=yes ;;
>  
> +  -runstatedir | --runstatedir | --runstatedi | --runstated \
> +  | --runstate | --runstat | --runsta | --runst | --runs \
> +  | --run | --ru | --r)
> +    ac_prev=runstatedir ;;
> +  -runstatedir=* | --runstatedir=* | --runstatedi=* | --runstated=* \
> +  | --runstate=* | --runstat=* | --runsta=* | --runst=* | --runs=* \
> +  | --run=* | --ru=* | --r=*)
> +    runstatedir=$ac_optarg ;;
> +
>    -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
>      ac_prev=sbindir ;;
>    -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \

Please use a non patched autoconf (usually debian based one adds the runstatedir).

> @@ -1234,7 +1245,7 @@ fi
>  for ac_var in	exec_prefix prefix bindir sbindir libexecdir datarootdir \
>  		datadir sysconfdir sharedstatedir localstatedir includedir \
>  		oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
> -		libdir localedir mandir
> +		libdir localedir mandir runstatedir
>  do
>    eval ac_val=\$$ac_var
>    # Remove trailing slashes.
> @@ -1387,6 +1398,7 @@ Fine tuning of the installation directories:
>    --sysconfdir=DIR        read-only single-machine data [PREFIX/etc]
>    --sharedstatedir=DIR    modifiable architecture-independent data [PREFIX/com]
>    --localstatedir=DIR     modifiable single-machine data [PREFIX/var]
> +  --runstatedir=DIR       modifiable per-process data [LOCALSTATEDIR/run]
>    --libdir=DIR            object code libraries [EPREFIX/lib]
>    --includedir=DIR        C header files [PREFIX/include]
>    --oldincludedir=DIR     C header files for non-gcc [/usr/include]
> @@ -6817,6 +6829,32 @@ if test $libc_cv_builtin_trap = yes; then
>  
>  fi
>  
> +# Check target support for 2MB variable alignment.
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for 2MB variable alignment" >&5
> +$as_echo_n "checking for 2MB variable alignment... " >&6; }
> +if ${libc_cv_have_2MB_alignment+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +
> +cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +
> +int foo __attribute__((aligned(0x200000))) = 1;
> +
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> +  libc_cv_have_2MB_alignment=yes
> +else
> +  libc_cv_have_2MB_alignment=no
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_have_2MB_alignment" >&5
> +$as_echo "$libc_cv_have_2MB_alignment" >&6; }
> +config_vars="$config_vars
> +have-2MB-alignment = $libc_cv_have_2MB_alignment"
> +
>  ac_ext=cpp
>  ac_cpp='$CXXCPP $CPPFLAGS'
>  ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
> diff --git a/configure.ac b/configure.ac
> index a91a7f399c..57d4572c26 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1726,6 +1726,17 @@ if test $libc_cv_builtin_trap = yes; then
>    AC_DEFINE([HAVE_BUILTIN_TRAP])
>  fi
>  
> +# Check target support for 2MB variable alignment.
> +AC_CACHE_CHECK([for 2MB variable alignment],
> +	       libc_cv_have_2MB_alignment, [
> +AC_COMPILE_IFELSE([AC_LANG_SOURCE([
> +int foo __attribute__((aligned(0x200000))) = 1;
> +])],
> +	       [libc_cv_have_2MB_alignment=yes],
> +	       [libc_cv_have_2MB_alignment=no])
> +])
> +LIBC_CONFIG_VAR([have-2MB-alignment], [$libc_cv_have_2MB_alignment])
> +
>  dnl C++ feature tests.
>  AC_LANG_PUSH([C++])
>  

Would be better to check 2 times the maximum supported pagesize instead?

> diff --git a/elf/Makefile b/elf/Makefile
> index fe42caeb0e..1bf77bc5ac 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -207,7 +207,7 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
>  	 tst-tls4 tst-tls5 \
>  	 tst-tls10 tst-tls11 tst-tls12 tst-tls13 tst-tls14 tst-tls15 \
>  	 tst-tls16 tst-tls17 tst-tls18 tst-tls19 tst-tls-dlinfo \
> -	 tst-align tst-align2 tst-align3 \
> +	 tst-align tst-align2 \
>  	 tst-dlmodcount tst-dlopenrpath tst-deep1 \
>  	 tst-dlmopen1 tst-dlmopen3 tst-dlmopen4 \
>  	 unload3 unload4 unload5 unload6 unload7 unload8 tst-global1 order2 \
> @@ -241,9 +241,6 @@ tests-internal += loadtest unload unload2 circleload1 \
>  tests-container += tst-pldd tst-dlopen-tlsmodid-container \
>    tst-dlopen-self-container tst-preload-pthread-libc
>  test-srcs = tst-pathopt
> -ifeq (yes,$(have-fpie))
> -tests-pie += tst-align3
> -endif
>  selinux-enabled := $(shell cat /selinux/enforce 2> /dev/null)
>  ifneq ($(selinux-enabled),1)
>  tests-execstack-yes = tst-execstack tst-execstack-needed tst-execstack-prog
> @@ -305,7 +302,7 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
>  		circlemod3 circlemod3a \
>  		reldep8mod1 reldep8mod2 reldep8mod3 \
>  		reldep9mod1 reldep9mod2 reldep9mod3 \
> -		tst-alignmod tst-alignmod2 tst-alignmod3 \
> +		tst-alignmod tst-alignmod2 \
>  		$(modules-execstack-$(have-z-execstack)) \
>  		tst-dlopenrpathmod tst-deep1mod1 tst-deep1mod2 tst-deep1mod3 \
>  		tst-dlmopen1mod tst-auditmod1 \
> @@ -418,6 +415,14 @@ endif
>  modules-execstack-yes = tst-execstack-mod
>  extra-test-objs += $(addsuffix .os,$(strip $(modules-names)))
>  
> +ifeq (yes,$(have-2MB-alignment))
> +tests += tst-align3
> +modules-names += tst-alignmod3
> +ifeq (yes,$(have-fpie))
> +tests-pie += tst-align3
> +endif
> +endif
> +
>  # filtmod1.so, tst-big-note-lib.so, tst-ro-dynamic-mod.so have special
>  # rules.
>  modules-names-nobuild := filtmod1 tst-big-note-lib tst-ro-dynamic-mod
>