[2/4] Check -z single-global-definition and -fsingle-global-definition
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Commit Message
1. Check linker support for -z single-global-definition. If
GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION is set on any input
relocatable files:
a. Don't generate copy relocations.
b. Turn off extern_protected_data.
c. Treate reference to protected symbols with single global definition
as local.
d. Set GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION on output.
e. Add -z [no]single-global-definition to control single global
definition.
2. Check compiler support for -fsingle-global-definition:
a. Generate a single global definition marker in relocatable objects.
i. Always use GOT to access undefined data and function symbols,
including in PIE and non-PIE. These will avoid copy relocations in
executables.
ii. This is compatible with existing executables and shared libraries.
b. In executable and shared library, bind symbols with the STV_PROTECTED
visibility locally:
i. The address of data symbol is the address of data body.
ii. For systems without function descriptor, the function pointer is
the address of function body.
iii. The resulting shared libraries may not be incompatible with
executables which have copy relocations on protected symbols.
Size comparison of non-PIE builds with GCC 12 -O2:
1. On x86-64:
text data bss dec hex filename
190218 9672 416 200306 30e72 ld.so (original)
190258 9336 416 200010 30d4a ld.so (-fsingle-global-definition)
1917384 20232 52424 1990040 1e5d98 libc.so (original)
1919946 20240 52432 1992618 1e67aa libc.so (-fsingle-global-definition)
261734 10339 744 272817 429b1 localedef (original)
233084 41734 648 275466 4340a localedef (-fsingle-global-definition)
2. On i686:
text data bss dec hex filename
199369 6796 212 206377 32629 ld.so (original)
199381 6796 212 206389 32635 ld.so (-fsingle-global-definition)
2058080 11136 38856 2108072 202aa8 libc.so (original)
2058092 11136 38856 2108084 202ab4 libc.so (-fsingle-global-definition)
276207 9559 552 286318 45e6e localedef (original)
254249 33734 520 288503 466f7 localedef (-fsingle-global-definition)
---
configure | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++-
configure.ac | 37 ++++++++++++++++++++++++++
2 files changed, 109 insertions(+), 1 deletion(-)
Comments
On Jun 20 2021, H.J. Lu via Libc-alpha wrote:
> diff --git a/configure b/configure
> index 9619c10991..5844dad68f 100755
> --- a/configure
> +++ b/configure
> @@ -732,6 +732,7 @@ infodir
> docdir
> oldincludedir
> includedir
> +runstatedir
> localstatedir
> sharedstatedir
> sysconfdir
Please use a vanilla autoconf version.
Andreas.
* H. J. Lu via Libc-alpha:
> 1. Check linker support for -z single-global-definition. If
> GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION is set on any input
> relocatable files:
> a. Don't generate copy relocations.
> b. Turn off extern_protected_data.
> c. Treate reference to protected symbols with single global definition
> as local.
> d. Set GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION on output.
> e. Add -z [no]single-global-definition to control single global
> definition.
> 2. Check compiler support for -fsingle-global-definition:
> a. Generate a single global definition marker in relocatable objects.
> i. Always use GOT to access undefined data and function symbols,
> including in PIE and non-PIE. These will avoid copy relocations in
> executables.
> ii. This is compatible with existing executables and shared libraries.
> b. In executable and shared library, bind symbols with the STV_PROTECTED
> visibility locally:
> i. The address of data symbol is the address of data body.
> ii. For systems without function descriptor, the function pointer is
> the address of function body.
> iii. The resulting shared libraries may not be incompatible with
> executables which have copy relocations on protected symbols.
>
> Size comparison of non-PIE builds with GCC 12 -O2:
>
> 1. On x86-64:
> text data bss dec hex filename
> 190218 9672 416 200306 30e72 ld.so (original)
> 190258 9336 416 200010 30d4a ld.so (-fsingle-global-definition)
> 1917384 20232 52424 1990040 1e5d98 libc.so (original)
> 1919946 20240 52432 1992618 1e67aa libc.so (-fsingle-global-definition)
> 261734 10339 744 272817 429b1 localedef (original)
> 233084 41734 648 275466 4340a localedef (-fsingle-global-definition)
I must say these numbers do not make sense to me. Why do libc.so and
localedef data sizes increase with -fsingle-global-definition? Fewer
copy relocations should *reduce* data size on both sides. localedef
would have to have nearly 4,000 data relocations to account for the size
increase. And shouldn't the GOT overlap with BSS anyway (so not even
show up in the data column)?
And I don't think we can build glibc with -fsingle-global-definition
anyway because it would be an ABI break.
> ---
> configure | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> configure.ac | 37 ++++++++++++++++++++++++++
> 2 files changed, 109 insertions(+), 1 deletion(-)
>
> diff --git a/configure b/configure
> index 9619c10991..5844dad68f 100755
> --- a/configure
> +++ b/configure
> @@ -732,6 +732,7 @@ infodir
> docdir
> oldincludedir
> includedir
> +runstatedir
> localstatedir
> sharedstatedir
> sysconfdir
Please regenerate with an unpatched autoconf.
Thanks,
Florian
On Mon, Jun 21, 2021 at 12:43 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> > 1. Check linker support for -z single-global-definition. If
> > GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION is set on any input
> > relocatable files:
> > a. Don't generate copy relocations.
> > b. Turn off extern_protected_data.
> > c. Treate reference to protected symbols with single global definition
> > as local.
> > d. Set GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION on output.
> > e. Add -z [no]single-global-definition to control single global
> > definition.
> > 2. Check compiler support for -fsingle-global-definition:
> > a. Generate a single global definition marker in relocatable objects.
> > i. Always use GOT to access undefined data and function symbols,
> > including in PIE and non-PIE. These will avoid copy relocations in
> > executables.
> > ii. This is compatible with existing executables and shared libraries.
> > b. In executable and shared library, bind symbols with the STV_PROTECTED
> > visibility locally:
> > i. The address of data symbol is the address of data body.
> > ii. For systems without function descriptor, the function pointer is
> > the address of function body.
> > iii. The resulting shared libraries may not be incompatible with
> > executables which have copy relocations on protected symbols.
> >
> > Size comparison of non-PIE builds with GCC 12 -O2:
> >
> > 1. On x86-64:
> > text data bss dec hex filename
> > 190218 9672 416 200306 30e72 ld.so (original)
> > 190258 9336 416 200010 30d4a ld.so (-fsingle-global-definition)
> > 1917384 20232 52424 1990040 1e5d98 libc.so (original)
> > 1919946 20240 52432 1992618 1e67aa libc.so (-fsingle-global-definition)
> > 261734 10339 744 272817 429b1 localedef (original)
> > 233084 41734 648 275466 4340a localedef (-fsingle-global-definition)
>
> I must say these numbers do not make sense to me. Why do libc.so and
> localedef data sizes increase with -fsingle-global-definition? Fewer
I haven't investigated them in detail yet. My main purposes were to
check if anything breaks.
> copy relocations should *reduce* data size on both sides. localedef
> would have to have nearly 4,000 data relocations to account for the size
> increase. And shouldn't the GOT overlap with BSS anyway (so not even
> show up in the data column)?
I will take a closer look.
> And I don't think we can build glibc with -fsingle-global-definition
> anyway because it would be an ABI break.
Correct.
> > ---
> > configure | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++-
> > configure.ac | 37 ++++++++++++++++++++++++++
> > 2 files changed, 109 insertions(+), 1 deletion(-)
> >
> > diff --git a/configure b/configure
> > index 9619c10991..5844dad68f 100755
> > --- a/configure
> > +++ b/configure
> > @@ -732,6 +732,7 @@ infodir
> > docdir
> > oldincludedir
> > includedir
> > +runstatedir
> > localstatedir
> > sharedstatedir
> > sysconfdir
>
> Please regenerate with an unpatched autoconf.
>
Will do.
Thanks.
@@ -732,6 +732,7 @@ infodir
docdir
oldincludedir
includedir
+runstatedir
localstatedir
sharedstatedir
sysconfdir
@@ -844,6 +845,7 @@ 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}'
@@ -1096,6 +1098,15 @@ 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=$ac_optarg ;;
+
-sbindir | --sbindir | --sbindi | --sbind | --sbin | --sbi | --sb)
ac_prev=sbindir ;;
-sbindir=* | --sbindir=* | --sbindi=* | --sbind=* | --sbin=* \
@@ -1233,7 +1244,7 @@ fi
for ac_var in exec_prefix prefix bindir sbindir libexecdir datarootdir \
datadir sysconfdir sharedstatedir localstatedir includedir \
oldincludedir docdir infodir htmldir dvidir pdfdir psdir \
- libdir localedir mandir
+ libdir localedir mandir runstatedir
do
eval ac_val=\$$ac_var
# Remove trailing slashes.
@@ -1386,6 +1397,7 @@ 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]
@@ -5746,6 +5758,65 @@ fi
$as_echo "$libc_cv_insert" >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking -z single-global-definition" >&5
+$as_echo_n "checking -z single-global-definition... " >&6; }
+if ${libc_cv_z_single_global_definition+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ cat > conftest.c <<EOF
+ __attribute__ ((visibility ("protected")))
+ void bar (void) {}
+ void *bar_p (void) { return &bar; }
+EOF
+ libc_cv_z_single_global_definition=no
+ if { ac_try='${CC-cc} -Wl,-z,single-global-definition
+ -nostdlib -nostartfiles $CFLAGS $CPPFLAGS $LDFLAGS
+ -fPIC -shared $no_ssp -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }; then
+ libc_cv_z_single_global_definition=yes
+ else
+ libc_cv_z_single_global_definition=no
+ fi
+ rm -f conftest.*
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_z_single_global_definition" >&5
+$as_echo "$libc_cv_z_single_global_definition" >&6; }
+config_vars="$config_vars
+have-z-single-global-definition = $libc_cv_z_single_global_definition"
+
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for -fsingle-global-definition" >&5
+$as_echo_n "checking for -fsingle-global-definition... " >&6; }
+if ${libc_cv_fsingle_global_definition+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ cat > conftest.c <<EOF
+int foo;
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -S
+ -fsingle-global-definition
+ conftest.c 1>&5'
+ { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+ (eval $ac_try) 2>&5
+ ac_status=$?
+ $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+ test $ac_status = 0; }; }; then
+ libc_cv_fsingle_global_definition=yes
+ else
+ libc_cv_fsingle_global_definition=no
+ fi
+ rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_fsingle_global_definition" >&5
+$as_echo "$libc_cv_fsingle_global_definition" >&6; }
+config_vars="$config_vars
+have-fsingle-global-definition = $libc_cv_fsingle_global_definition"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for broken __attribute__((alias()))" >&5
$as_echo_n "checking for broken __attribute__((alias()))... " >&6; }
if ${libc_cv_broken_alias_attribute+:} false; then :
@@ -1222,6 +1222,43 @@ EOF
])
AC_SUBST(libc_cv_insert)
+AC_CACHE_CHECK(-z single-global-definition,
+ libc_cv_z_single_global_definition,
+ [cat > conftest.c <<EOF
+ __attribute__ ((visibility ("protected")))
+ void bar (void) {}
+ void *bar_p (void) { return &bar; }
+EOF
+ libc_cv_z_single_global_definition=no
+ if AC_TRY_COMMAND([${CC-cc} -Wl,-z,single-global-definition
+ -nostdlib -nostartfiles $CFLAGS $CPPFLAGS $LDFLAGS
+ -fPIC -shared $no_ssp -o conftest.so conftest.c
+ 1>&AS_MESSAGE_LOG_FD]); then
+ libc_cv_z_single_global_definition=yes
+ else
+ libc_cv_z_single_global_definition=no
+ fi
+ rm -f conftest.*
+ ])
+LIBC_CONFIG_VAR([have-z-single-global-definition],
+ [$libc_cv_z_single_global_definition])
+
+AC_CACHE_CHECK(for -fsingle-global-definition,
+ libc_cv_fsingle_global_definition,
+ [cat > conftest.c <<EOF
+int foo;
+EOF
+ if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS -S
+ -fsingle-global-definition
+ conftest.c 1>&AS_MESSAGE_LOG_FD]); then
+ libc_cv_fsingle_global_definition=yes
+ else
+ libc_cv_fsingle_global_definition=no
+ fi
+ rm -f conftest*])
+LIBC_CONFIG_VAR([have-fsingle-global-definition],
+ [$libc_cv_fsingle_global_definition])
+
AC_CACHE_CHECK(for broken __attribute__((alias())),
libc_cv_broken_alias_attribute,
[cat > conftest.c <<EOF