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List: glibc-cvs
Subject: [glibc/google/grte/v5-2.27/master] Set the retain attribute on _elf_set_element if CC supports [BZ #
From: Fangrui Song via Glibc-cvs <glibc-cvs () sourceware ! org>
Date: 2021-08-31 23:15:28
Message-ID: 20210831231528.BEF273858C27 () sourceware ! org
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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=add8e34cd7223dc6770c34de820651eee879ff65
commit add8e34cd7223dc6770c34de820651eee879ff65
Author: Fangrui Song <maskray@google.com>
Date: Fri Apr 16 11:26:39 2021 -0700
Set the retain attribute on _elf_set_element if CC supports [BZ #27492]
So that text_set_element/data_set_element/bss_set_element defined
variables will be retained by the linker.
Note: 'used' and 'retain' are orthogonal: 'used' makes sure the variable
will not be optimized out; 'retain' prevents section garbage collection
if the linker support SHF_GNU_RETAIN.
GNU ld 2.37 and LLD 13 will support -z start-stop-gc which allow C
identifier name sections to be GCed even if there are live
__start_/__stop_ references.
Without the change, there are some static linking problems, e.g.
_IO_cleanup (libio/genops.c) may be discarded by ld --gc-sections, so
stdout is not flushed on exit.
Note: GCC may warning 'retain' attribute ignored while __has_attribute(retain)
is 1 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99587).
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
(cherry picked from commit cd6ae7ea5431c2b8f16201fb0e2c413bf8d2df06)
Diff:
---
config.h.in | 3 ++
configure | 59 ++++++++++++++++++++++++++++++
configure.ac | 21 +++++++++++
include/libc-symbols.h | 14 +++++--
libio/Makefile | 28 ++++++++++++++
libio/tst-cleanup-default-static.c | 1 +
libio/tst-cleanup-default.c | 1 +
libio/tst-cleanup-nostart-stop-gc-static.c | 1 +
libio/tst-cleanup-nostart-stop-gc.c | 1 +
libio/tst-cleanup-start-stop-gc-static.c | 1 +
libio/tst-cleanup-start-stop-gc.c | 1 +
libio/tst-cleanup.c | 34 +++++++++++++++++
libio/tst-cleanup.exp | 1 +
13 files changed, 162 insertions(+), 4 deletions(-)
diff --git a/config.h.in b/config.h.in
index 2aed757829..7385ddd1e4 100644
--- a/config.h.in
+++ b/config.h.in
@@ -171,6 +171,9 @@
/* Define if gcc supports attribute ifunc. */
#undef HAVE_GCC_IFUNC
+/* Define if CC supports attribute retain. */
+#undef HAVE_GNU_RETAIN
+
#define WANT_FLOAT128 0
/*
diff --git a/configure b/configure
index f033eef082..9fd2eaa1bc 100755
--- a/configure
+++ b/configure
@@ -4061,6 +4061,31 @@ fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_indirect_function" >&5
$as_echo "$libc_cv_gcc_indirect_function" >&6; }
+# Check if CC supports attribute retain as it is used in attribute_used_retain \
macro. +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for GNU attribute retain \
support" >&5 +$as_echo_n "checking for GNU attribute retain support... " >&6; }
+if ${libc_cv_gnu_retain+:} false; then :
+ $as_echo_n "(cached) " >&6
+else
+ cat > conftest.c <<EOF
+static int var __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&5 \
+ 2>&5 ; then
+ libc_cv_gnu_retain=yes
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gnu_retain" >&5
+$as_echo "$libc_cv_gnu_retain" >&6; }
+if test $libc_cv_gnu_retain = yes; then
+ $as_echo "#define HAVE_GNU_RETAIN 1" >>confdefs.h
+
+fi
+config_vars="$config_vars
+have-gnu-retain = $libc_cv_gnu_retain"
+
# Check if gcc warns about alias for function with incompatible types.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for \
function with incompatible types" >&5 $as_echo_n "checking if compiler warns about \
alias for function with incompatible types... " >&6; } @@ -5884,6 +5909,40 @@ fi
$as_echo "$libc_linker_feature" >&6; }
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z \
start-stop-gc" >&5 +$as_echo_n "checking for linker that supports -z start-stop-gc... \
" >&6; } +libc_linker_feature=no
+if test x"$gnu_ld" = x"yes"; then
+ libc_linker_check=`$LD -v --help 2>/dev/null | grep "\-z start-stop-gc"`
+ if test -n "$libc_linker_check"; then
+ cat > conftest.c <<EOF
+int _start (void) { return 42; }
+EOF
+ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
+ -Wl,-z,start-stop-gc -nostdlib -nostartfiles
+ -fPIC -shared -o conftest.so conftest.c
+ 1>&5'
+ { { eval echo "\"\$as_me\":${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_linker_feature=yes
+ fi
+ rm -f conftest*
+ fi
+fi
+if test $libc_linker_feature = yes; then
+ libc_cv_z_start_stop_gc=yes
+else
+ libc_cv_z_start_stop_gc=no
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
+$as_echo "$libc_linker_feature" >&6; }
+config_vars="$config_vars
+have-z-start-stop-gc = $libc_cv_z_start_stop_gc"
+
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker that supports \
--no-dynamic-linker" >&5 $as_echo_n "checking for linker that supports \
--no-dynamic-linker... " >&6; } libc_linker_feature=no
diff --git a/configure.ac b/configure.ac
index 6197321742..cad59fa94f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -670,6 +670,23 @@ if ${CC-cc} -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD \
fi
rm -f conftest*])
+# Check if CC supports attribute retain as it is used in attribute_used_retain \
macro. +AC_CACHE_CHECK([for GNU attribute retain support],
+ libc_cv_gnu_retain, [dnl
+cat > conftest.c <<EOF
+static int var __attribute__ ((used, retain, section ("__libc_atexit")));
+EOF
+libc_cv_gnu_retain=no
+if ${CC-cc} -Werror -c conftest.c -o /dev/null 1>&AS_MESSAGE_LOG_FD \
+ 2>&AS_MESSAGE_LOG_FD ; then
+ libc_cv_gnu_retain=yes
+fi
+rm -f conftest*])
+if test $libc_cv_gnu_retain = yes; then
+ AC_DEFINE(HAVE_GNU_RETAIN)
+fi
+LIBC_CONFIG_VAR([have-gnu-retain], [$libc_cv_gnu_retain])
+
# Check if gcc warns about alias for function with incompatible types.
AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
libc_cv_gcc_incompatible_alias, [dnl
@@ -1333,6 +1350,10 @@ LIBC_LINKER_FEATURE([-z execstack], [-Wl,-z,execstack],
[libc_cv_z_execstack=yes], [libc_cv_z_execstack=no])
AC_SUBST(libc_cv_z_execstack)
+LIBC_LINKER_FEATURE([-z start-stop-gc], [-Wl,-z,start-stop-gc],
+ [libc_cv_z_start_stop_gc=yes], [libc_cv_z_start_stop_gc=no])
+LIBC_CONFIG_VAR([have-z-start-stop-gc], [$libc_cv_z_start_stop_gc])
+
LIBC_LINKER_FEATURE([--no-dynamic-linker],
[-Wl,--no-dynamic-linker],
[libc_cv_no_dynamic_linker=yes],
diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index c40f5fb6ca..1e00fcb33e 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -286,6 +286,12 @@ for linking")
*/
+#ifdef HAVE_GNU_RETAIN
+# define attribute_used_retain __attribute__ ((__used__, __retain__))
+#else
+# define attribute_used_retain __attribute__ ((__used__))
+#endif
+
/* Symbol set support macros. */
/* Make SYMBOL, which is in the text segment, an element of SET. */
@@ -301,12 +307,12 @@ for linking")
/* When building a shared library, make the set section writable,
because it will need to be relocated at run time anyway. */
# define _elf_set_element(set, symbol) \
- static const void *__elf_set_##set##_element_##symbol##__ \
- __attribute__ ((used, section (#set))) = &(symbol)
+ static const void *__elf_set_##set##_element_##symbol##__ \
+ attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
#else
# define _elf_set_element(set, symbol) \
- static const void *const __elf_set_##set##_element_##symbol##__ \
- __attribute__ ((used, section (#set))) = &(symbol)
+ static const void *const __elf_set_##set##_element_##symbol##__ \
+ attribute_used_retain __attribute__ ((section (#set))) = &(symbol)
#endif
/* Define SET as a symbol set. This may be required (it is in a.out) to
diff --git a/libio/Makefile b/libio/Makefile
index 918a86bb74..bc4cd3456a 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -177,6 +177,26 @@ ifeq (yes,$(build-shared))
# library is enabled since they depend on tst-fopenloc.out.
tests-special += $(objpfx)tst-fopenloc-cmp.out $(objpfx)tst-fopenloc-mem.out
endif
+
+tests += tst-cleanup-default tst-cleanup-default-static
+tests-static += tst-cleanup-default-static
+tests-special += $(objpfx)tst-cleanup-default-cmp.out \
$(objpfx)tst-cleanup-default-static-cmp.out +LDFLAGS-tst-cleanup-default = \
-Wl,--gc-sections +LDFLAGS-tst-cleanup-default-static = -Wl,--gc-sections
+
+ifeq ($(have-gnu-retain)$(have-z-start-stop-gc),yesyes)
+tests += tst-cleanup-start-stop-gc tst-cleanup-start-stop-gc-static \
+ tst-cleanup-nostart-stop-gc tst-cleanup-nostart-stop-gc-static
+tests-static += tst-cleanup-start-stop-gc-static tst-cleanup-nostart-stop-gc-static
+tests-special += $(objpfx)tst-cleanup-start-stop-gc-cmp.out \
+ $(objpfx)tst-cleanup-start-stop-gc-static-cmp.out \
+ $(objpfx)tst-cleanup-nostart-stop-gc-cmp.out \
+ $(objpfx)tst-cleanup-nostart-stop-gc-static-cmp.out
+LDFLAGS-tst-cleanup-start-stop-gc := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-start-stop-gc-static := -Wl,--gc-sections,-z,start-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc := -Wl,--gc-sections,-z,nostart-stop-gc
+LDFLAGS-tst-cleanup-nostart-stop-gc-static := -Wl,--gc-sections,-z,nostart-stop-gc
+endif
endif
include ../Rules
@@ -205,6 +225,14 @@ $(objpfx)tst-widetext.out: $(gen-locales)
$(objpfx)tst_wprintf2.out: $(gen-locales)
endif
+define gen-tst-cleanup
+$(objpfx)tst-cleanup-$1-cmp.out: tst-cleanup.exp $(objpfx)tst-cleanup-$1.out
+ cmp $$^ > $$@; $$(evaluate-test)
+endef
+
+$(foreach t,default default-static start-stop-gc start-stop-gc-static \
nostart-stop-gc nostart-stop-gc-static, \ + $(eval $(call gen-tst-cleanup,$(t))))
+
$(objpfx)test-freopen.out: test-freopen.sh $(objpfx)test-freopen
$(SHELL) $< $(common-objpfx) '$(test-program-prefix)' \
$(common-objpfx)libio/ > $@; \
diff --git a/libio/tst-cleanup-default-static.c b/libio/tst-cleanup-default-static.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-default-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-default.c b/libio/tst-cleanup-default.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-default.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-nostart-stop-gc-static.c \
b/libio/tst-cleanup-nostart-stop-gc-static.c new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-nostart-stop-gc-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-nostart-stop-gc.c \
b/libio/tst-cleanup-nostart-stop-gc.c new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-nostart-stop-gc.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-start-stop-gc-static.c \
b/libio/tst-cleanup-start-stop-gc-static.c new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-start-stop-gc-static.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup-start-stop-gc.c b/libio/tst-cleanup-start-stop-gc.c
new file mode 100644
index 0000000000..c39956e2a8
--- /dev/null
+++ b/libio/tst-cleanup-start-stop-gc.c
@@ -0,0 +1 @@
+#include "tst-cleanup.c"
diff --git a/libio/tst-cleanup.c b/libio/tst-cleanup.c
new file mode 100644
index 0000000000..837feac164
--- /dev/null
+++ b/libio/tst-cleanup.c
@@ -0,0 +1,34 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+/* Test that stdout is flushed after atexit callbacks were run, even if the
+ * executable is linked with --gc-sections. */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void
+hook (void)
+{
+ puts ("hello");
+}
+
+int
+main (void)
+{
+ atexit (hook);
+}
diff --git a/libio/tst-cleanup.exp b/libio/tst-cleanup.exp
new file mode 100644
index 0000000000..ce01362503
--- /dev/null
+++ b/libio/tst-cleanup.exp
@@ -0,0 +1 @@
+hello
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