When we have a weak reference to a symbol defined in an
as-needed library, and that library ends up not-needed, gold
simply clears the version information in the symbol table, even
if the symbol could have been resolved by a needed library later
in the link order. This results in a loss of version information,
which can cause the program to bind to the wrong version at run
time.
This patch lets a dynamic definition override an earlier one if
the earlier one is from a not-needed library, so that we can
retain the version information from the binding to the needed
library. In order to do that, the tracking of needed/not-needed
had to be moved up to symbol resolution time, instead of during
Symbol_table::set_dynsym_indexes().
In cases where we still end up discarding version information,
I've added a warning.
For the original problem report and discussion, see:
https://stackoverflow.com/questions/
50751421/undefined-behavior-in-shared-lib-using-libpthread-but-not-having-it-in-elf-as-d
gold/
* resolve.cc (Symbol_table::resolve): Rename tobinding to
orig_tobinding. Call set_is_needed() for objects that resolve
non-weak references.
(Symbol_table::should_override): Allow a dynamic definition to
override an earlier one in a not-needed library.
* symtab.cc (Symbol_table::set_dynsym_indexes): Remove separate
processing for as-needed symbols. Add warning when discarding
version informatin.
* testsuite/Makefile.am (weak_as_needed): New test case.
* testsuite/Makefile.in: Regenerate.
* testsuite/weak_as_needed.sh: New test script.
* testsuite/weak_as_needed_a.c: New source file.
* testsuite/weak_as_needed_b.c: New source file.
* testsuite/weak_as_needed_b.script: New version script.
* testsuite/weak_as_needed_c.c: New source file.
* testsuite/weak_as_needed_c.script: New version script.
+2018-06-21 Cary Coutant <ccoutant@gmail.com>
+
+ * resolve.cc (Symbol_table::resolve): Rename tobinding to
+ orig_tobinding. Call set_is_needed() for objects that resolve
+ non-weak references.
+ (Symbol_table::should_override): Allow a dynamic definition to
+ override an earlier one in a not-needed library.
+ * symtab.cc (Symbol_table::set_dynsym_indexes): Remove separate
+ processing for as-needed symbols. Add warning when discarding
+ version informatin.
+ * testsuite/Makefile.am (weak_as_needed): New test case.
+ * testsuite/Makefile.in: Regenerate.
+ * testsuite/weak_as_needed.sh: New test script.
+ * testsuite/weak_as_needed_a.c: New source file.
+ * testsuite/weak_as_needed_b.c: New source file.
+ * testsuite/weak_as_needed_b.script: New version script.
+ * testsuite/weak_as_needed_c.c: New source file.
+ * testsuite/weak_as_needed_c.script: New version script.
+
2018-06-20 Cary Coutant <ccoutant@gmail.com>
PR gold/23268
object, &adjust_common_sizes,
&adjust_dyndef, is_default_version))
{
- elfcpp::STB tobinding = to->binding();
+ elfcpp::STB orig_tobinding = to->binding();
typename Sized_symbol<size>::Value_type tovalue = to->value();
this->override(to, sym, st_shndx, is_ordinary, object, version);
if (adjust_common_sizes)
{
// We are overriding an UNDEF or WEAK UNDEF with a DYN DEF.
// Remember which kind of UNDEF it was for future reference.
- to->set_undef_binding(tobinding);
+ to->set_undef_binding(orig_tobinding);
}
}
else
to->override_visibility(sym.get_st_visibility());
}
+ // If we have a non-WEAK reference from a regular object to a
+ // dynamic object, mark the dynamic object as needed.
+ if (to->is_from_dynobj() && to->in_reg() && !to->is_undef_binding_weak())
+ to->object()->set_is_needed();
+
if (adjust_common_sizes && parameters->options().warn_common())
{
if (tosize > sym.get_st_size())
&& to->version() == NULL
&& is_default_version)
return true;
+ // Or, if the existing definition is in an unused --as-needed library,
+ // and the reference is weak, let the new definition override.
+ if (to->in_reg()
+ && to->is_undef_binding_weak()
+ && to->object()->as_needed()
+ && !to->object()->is_needed())
+ return true;
return false;
case UNDEF * 16 + DYN_DEF:
case COMMON * 16 + DYN_DEF:
case WEAK_COMMON * 16 + DYN_DEF:
- case DYN_COMMON * 16 + DYN_DEF:
- case DYN_WEAK_COMMON * 16 + DYN_DEF:
// Ignore a dynamic definition if we already have a common
// definition.
return false;
case DEF * 16 + DYN_WEAK_DEF:
case WEAK_DEF * 16 + DYN_WEAK_DEF:
- case DYN_DEF * 16 + DYN_WEAK_DEF:
- case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
// Ignore a weak dynamic definition if we already have a
// definition.
return false;
case COMMON * 16 + DYN_WEAK_DEF:
case WEAK_COMMON * 16 + DYN_WEAK_DEF:
- case DYN_COMMON * 16 + DYN_WEAK_DEF:
- case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
// Ignore a weak dynamic definition if we already have a common
// definition.
return false;
+ case DYN_COMMON * 16 + DYN_DEF:
+ case DYN_WEAK_COMMON * 16 + DYN_DEF:
+ case DYN_DEF * 16 + DYN_WEAK_DEF:
+ case DYN_WEAK_DEF * 16 + DYN_WEAK_DEF:
+ case DYN_COMMON * 16 + DYN_WEAK_DEF:
+ case DYN_WEAK_COMMON * 16 + DYN_WEAK_DEF:
+ // If the existing definition is in an unused --as-needed library,
+ // and the reference is weak, let a new dynamic definition override.
+ if (to->in_reg()
+ && to->is_undef_binding_weak()
+ && to->object()->as_needed()
+ && !to->object()->is_needed())
+ return true;
+ return false;
+
case DEF * 16 + UNDEF:
case WEAK_DEF * 16 + UNDEF:
case UNDEF * 16 + UNDEF:
Stringpool* dynpool,
Versions* versions)
{
- std::vector<Symbol*> as_needed_sym;
-
// First process all the symbols which have been forced to be local,
// as they must appear before all global symbols.
unsigned int forced_local_count = 0;
syms->push_back(sym);
dynpool->add(sym->name(), false, NULL);
- // If the symbol is defined in a dynamic object and is
- // referenced strongly in a regular object, then mark the
- // dynamic object as needed. This is used to implement
- // --as-needed.
- if (sym->is_from_dynobj()
- && sym->in_reg()
- && !sym->is_undef_binding_weak())
- sym->object()->set_is_needed();
-
// Record any version information, except those from
// as-needed libraries not seen to be needed. Note that the
// is_needed state for such libraries can change in this loop.
|| sym->object()->is_needed())
versions->record_version(this, dynpool, sym);
else
- as_needed_sym.push_back(sym);
+ {
+ gold_warning(_("discarding version information for "
+ "%s@%s, defined in unused shared library %s "
+ "(linked with --as-needed)"),
+ sym->name(), sym->version(),
+ sym->object()->name().c_str());
+ sym->clear_version();
+ }
}
}
}
- // Process version information for symbols from as-needed libraries.
- for (std::vector<Symbol*>::iterator p = as_needed_sym.begin();
- p != as_needed_sym.end();
- ++p)
- {
- Symbol* sym = *p;
-
- if (sym->object()->is_needed())
- versions->record_version(this, dynpool, sym);
- else
- sym->clear_version();
- }
-
// Finish up the versions. In some cases this may add new dynamic
// symbols.
index = versions->finalize(this, index, syms);
ver_test_14: gcctestdir/ld ver_test_main.o ver_test_1.so ver_test_2.so ver_test_4.so ver_test_14.script
$(CXXLINK) -Bgcctestdir/ -Wl,--version-script,$(srcdir)/ver_test_14.script -Wl,-E -Wl,-R,. ver_test_main.o ver_test_1.so ver_test_2.so ver_test_4.so
+check_SCRIPTS += weak_as_needed.sh
+check_DATA += weak_as_needed.stdout
+weak_as_needed.stdout: weak_as_needed_a.so
+ $(TEST_READELF) -dW --dyn-syms $< >$@
+weak_as_needed_a.so: gcctestdir/ld weak_as_needed_a.o weak_as_needed_b.so weak_as_needed_c.so
+ gcctestdir/ld -shared -rpath . -o $@ weak_as_needed_a.o --as-needed weak_as_needed_b.so weak_as_needed_c.so
+weak_as_needed_b.so: gcctestdir/ld weak_as_needed_b.o weak_as_needed_b.script
+ gcctestdir/ld -shared -rpath . -o $@ --version-script $(srcdir)/weak_as_needed_b.script weak_as_needed_b.o
+weak_as_needed_c.so: gcctestdir/ld weak_as_needed_c.o weak_as_needed_c.script
+ gcctestdir/ld -shared -rpath . -o $@ --version-script $(srcdir)/weak_as_needed_c.script weak_as_needed_c.o
+weak_as_needed_a.o: weak_as_needed_a.c
+ $(COMPILE) -c -fpic -o $@ $<
+weak_as_needed_b.o: weak_as_needed_b.c
+ $(COMPILE) -c -fpic -o $@ $<
+weak_as_needed_c.o: weak_as_needed_c.c
+ $(COMPILE) -c -fpic -o $@ $<
+
check_PROGRAMS += protected_1
protected_1_SOURCES = \
protected_main_1.cc protected_main_2.cc protected_main_3.cc
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_4.sh ver_test_5.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_7.sh ver_test_8.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_10.sh ver_test_13.sh \
-@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_14.sh relro_test.sh \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_14.sh weak_as_needed.sh \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ relro_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_matching_test.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ script_test_3.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ script_test_4.sh \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_8_2.so.syms \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_10.syms \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_13.syms \
-@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_14.syms protected_3.err \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_test_14.syms \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ weak_as_needed.stdout \
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ protected_3.err \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ relro_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ ver_matching_test.stdout \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ script_test_3.stdout \
--log-file $$b.log --trs-file $$b.trs \
$(am__common_driver_flags) $(AM_LOG_DRIVER_FLAGS) $(LOG_DRIVER_FLAGS) -- $(LOG_COMPILE) \
"$$tst" $(AM_TESTS_FD_REDIRECT)
+weak_as_needed.sh.log: weak_as_needed.sh
+ @p='weak_as_needed.sh'; \
+ b='weak_as_needed.sh'; \
+ $(am__check_pre) $(LOG_DRIVER) --test-name "$$f" \
+ --log-file $$b.log --trs-file $$b.trs \
+ $(am__common_driver_flags) $(AM_LOG_DRIVER_FLAGS) $(LOG_DRIVER_FLAGS) -- $(LOG_COMPILE) \
+ "$$tst" $(AM_TESTS_FD_REDIRECT)
relro_test.sh.log: relro_test.sh
@p='relro_test.sh'; \
b='relro_test.sh'; \
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_OBJDUMP) -T $< | $(TEST_CXXFILT) >$@
@GCC_TRUE@@NATIVE_LINKER_TRUE@ver_test_14: gcctestdir/ld ver_test_main.o ver_test_1.so ver_test_2.so ver_test_4.so ver_test_14.script
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -Wl,--version-script,$(srcdir)/ver_test_14.script -Wl,-E -Wl,-R,. ver_test_main.o ver_test_1.so ver_test_2.so ver_test_4.so
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed.stdout: weak_as_needed_a.so
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(TEST_READELF) -dW --dyn-syms $< >$@
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_a.so: gcctestdir/ld weak_as_needed_a.o weak_as_needed_b.so weak_as_needed_c.so
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ gcctestdir/ld -shared -rpath . -o $@ weak_as_needed_a.o --as-needed weak_as_needed_b.so weak_as_needed_c.so
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_b.so: gcctestdir/ld weak_as_needed_b.o weak_as_needed_b.script
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ gcctestdir/ld -shared -rpath . -o $@ --version-script $(srcdir)/weak_as_needed_b.script weak_as_needed_b.o
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_c.so: gcctestdir/ld weak_as_needed_c.o weak_as_needed_c.script
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ gcctestdir/ld -shared -rpath . -o $@ --version-script $(srcdir)/weak_as_needed_c.script weak_as_needed_c.o
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_a.o: weak_as_needed_a.c
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(COMPILE) -c -fpic -o $@ $<
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_b.o: weak_as_needed_b.c
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(COMPILE) -c -fpic -o $@ $<
+@GCC_TRUE@@NATIVE_LINKER_TRUE@weak_as_needed_c.o: weak_as_needed_c.c
+@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(COMPILE) -c -fpic -o $@ $<
@GCC_TRUE@@NATIVE_LINKER_TRUE@protected_1.so: gcctestdir/ld protected_1_pic.o protected_2_pic.o protected_3_pic.o
@GCC_TRUE@@NATIVE_LINKER_TRUE@ $(CXXLINK) -Bgcctestdir/ -shared protected_1_pic.o protected_2_pic.o protected_3_pic.o
--- /dev/null
+#!/bin/sh
+
+# weak_as_needed.sh -- a test case for version handling with weak symbols
+# and --as-needed libraries.
+
+# Copyright (C) 2018 Free Software Foundation, Inc.
+# Written by Cary Coutant <ccoutant@gmail.com>.
+
+# This file is part of gold.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+
+# This program 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 General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+
+# This test verifies that a weak reference is properly bound to
+# an as-needed library, when it is first resolved to a symbol in
+# a library that ends up being not needed.
+
+# Ref: https://stackoverflow.com/questions/50751421/undefined-behavior-in-shared-lib-using-libpthread-but-not-having-it-in-elf-as-d
+
+check()
+{
+ if ! grep -q "$2" "$1"
+ then
+ echo "Did not find expected output in $1:"
+ echo " $2"
+ echo ""
+ echo "Actual output below:"
+ cat "$1"
+ exit 1
+ fi
+}
+
+check_missing()
+{
+ if grep -q "$2" "$1"
+ then
+ echo "Found unexpected output in $1:"
+ echo " $2"
+ echo ""
+ echo "Actual output below:"
+ cat "$1"
+ exit 1
+ fi
+}
+
+check weak_as_needed.stdout "WEAK .* UND *bar@v2"
+check weak_as_needed.stdout "NEEDED.*weak_as_needed_c\.so"
+check_missing weak_as_needed.stdout "NEEDED.*weak_as_needed_b\.so"
+
+exit 0
--- /dev/null
+extern void bar(void) __attribute__ (( weak ));
+extern void t4(void);
+
+void foo(void);
+
+void foo(void)
+{
+ bar();
+ t4();
+}
--- /dev/null
+#include <stdio.h>
+
+__asm__ (".symver bar_v1, bar@v1");
+__asm__ (".symver bar_v2, bar@@v2");
+
+void bar_v1(void);
+void bar_v2(void);
+void baz(void);
+
+void bar_v1(void)
+{
+ printf("weak_as_needed_b: bar_v1\n");
+}
+
+void bar_v2(void)
+{
+ printf("weak_as_needed_b: bar_v2\n");
+}
+
+void baz(void)
+{
+ printf("weak_as_needed_b: baz\n");
+}
--- /dev/null
+v1 {
+ global:
+ bar;
+};
+v2 {
+ global:
+ bar;
+ baz;
+ local:
+ *;
+} v1;
--- /dev/null
+#include <stdio.h>
+
+__asm__ (".symver bar_v1, bar@v1");
+__asm__ (".symver bar_v2, bar@@v2");
+
+void bar_v1(void);
+void bar_v2(void);
+void baz(void);
+void t4(void);
+
+void bar_v1(void)
+{
+ printf("weak_as_needed_c: bar_v1\n");
+}
+
+void bar_v2(void)
+{
+ printf("weak_as_needed_c: bar_v2\n");
+}
+
+void baz(void)
+{
+ printf("weak_as_needed_c: baz\n");
+}
+
+void t4(void)
+{
+ printf("weak_as_needed_c: t4\n");
+}
--- /dev/null
+v1 {
+ global:
+ bar;
+};
+v2 {
+ global:
+ bar;
+ baz;
+ t4;
+ local:
+ *;
+} v1;
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