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

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

On 10/12/2021 18:54, H.J. Lu wrote:
> On Fri, Dec 10, 2021 at 1:36 PM Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> 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=$ac_optarg ;;
>>> +
>>>    -sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
>>>      ac_prev=sbindir ;;
>>>    -sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
>>
>> Please use a non patched autoconf (usually debian based one adds the runstatedir).
> 
> Fixed.
> 
>>> @@ -1234,7 +1245,7 @@ fi
>>>  for ac_var in        exec_prefix prefix bindir sbindir libexecdir datarootdir \
>>>               datadir sysconfdir sharedstatedir localstatedir includedir \
>>>               oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
>>> -             libdir localedir mandir
>>> +             libdir localedir mandir runstatedir
>>>  do
>>>    eval ac_val=\$$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?
> 
> Why 2 times?  The test only uses 2MB alignment.  The implementation
> self doesn't depend on the maximum supported page size.   The limit
> is available free address space.

It is an arbitrary value larger than the pagesize to make the test check
for it even on architecture that do no support 2MB alignment.