Fix treatment of symbol versions with unused as-needed libraries.

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.

1 files changed, 26 insertions, 2 deletions

diff --git a/gold/testsuite/Makefile.in b/gold/testsuite/Makefile.in
index e1b1762..14e4ce5 100644
--- a/gold/testsuite/Makefile.in
+++ b/gold/testsuite/Makefile.in
@@ -479,7 +479,8 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3) \
 @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 \
@@ -534,7 +535,9 @@ check_PROGRAMS = $(am__EXEEXT_1) $(am__EXEEXT_2) $(am__EXEEXT_3) \
 @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 \
@@ -5802,6 +5805,13 @@ ver_test_14.sh.log: ver_test_14.sh
 	--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'; \
@@ -8712,6 +8722,20 @@ uninstall-am:
 @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