Re: [PATCH v2] Check alignment of PT_LOAD segment only if possible

[Rongwei Wang <rongwei.wang@linux.alibaba.com>]

On 12/11/21 6:02 AM, H.J. Lu via Libc-alpha 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    | 26 ++++++++++++++++++++++++++
>   configure.ac | 11 +++++++++++
>   elf/Makefile | 15 ++++++++++-----
>   3 files changed, 47 insertions(+), 5 deletions(-)
> 
> diff --git a/configure b/configure
> index e4d013907c..37259efce7 100755
> --- a/configure
> +++ b/configure
> @@ -6817,6 +6817,32 @@ 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++])
>   
> 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
> 
Hello

It seems that I need to wait for this patch to merge before I can send 
out the following patch again:
"Add a testcase to check alignment of PT_LOAD segment"

I am not sure if I got it right. If I missing something, please let me know.

Thanks.