elf: when relocating do not lookup STB_LOCAL symbols by name

As the issue #1065 describes, some linkers (like gold) in certain scenarios generate
ELF objects that end up with symbols with local binding (STB_LOCAL) that need
to be relocated. The known concrete scenarios involve symbols of type STT_SECTION
and STT_TLS which fail to get relocated by OSv linker as it attempts to look
them up by name and they are not present in the relevant string lookup tables
or worse point to the empty name in the string table at index 0.

To address it we follow what Musl does which is simply looking
such symbols by index in the current ELF object instead of by name.

This patch also adds extra unit test that fails without this patch
to prove that the fix is correct.

Fixes #1065

Signed-off-by: Waldemar Kozaczuk <jwkozaczuk@gmail.com>
Message-Id: <20191223170751.7166-1-jwkozaczuk@gmail.com>

Author: wkozaczuk

core/elf.cc

@@ -642,10 +642,13 @@ symbol_module object::symbol(unsigned idx, bool ignore_missing)
     auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
     assert(dynamic_val(DT_SYMENT) == sizeof(Elf64_Sym));
     auto sym = &symtab[idx];
+    auto binding = symbol_binding(*sym);
+    if (binding == STB_LOCAL) {
+        return symbol_module(sym, this);
+    }
     auto nameidx = sym->st_name;
     auto name = dynamic_ptr<const char>(DT_STRTAB) + nameidx;
     auto ret = _prog.lookup(name);
-    auto binding = symbol_binding(*sym);
     if (!ret.symbol && binding == STB_WEAK) {
         return symbol_module(sym, this);
     }

modules/tests/Makefile

@@ -119,7 +119,7 @@ tests := tst-pthread.so misc-ramdisk.so tst-vblk.so tst-bsd-evh.so \
 	tst-sendfile.so misc-lock-perf.so tst-uio.so tst-printf.so \
 	tst-pthread-affinity.so tst-pthread-tsd.so tst-thread-local.so \
 	tst-zfs-mount.so tst-regex.so tst-tcp-siocoutq.so \
-	libtls.so tst-tls.so tst-tls-pie.so tst-select-timeout.so tst-faccessat.so \
+	libtls.so libtls_gold.so tst-tls.so tst-tls-gold.so tst-tls-pie.so tst-select-timeout.so tst-faccessat.so \
 	tst-fstatat.so misc-reboot.so tst-fcntl.so payload-namespace.so \
 	tst-namespace.so tst-without-namespace.so payload-env.so \
 	payload-merge-env.so misc-execve.so misc-execve-payload.so misc-mutex2.so \
@@ -162,6 +162,18 @@ $(out)/tests/tst-tls-pie.so: \
 	$(makedir)
 	$(call quiet, cd $(out); $(CXX) $(CXXFLAGS) -fuse-ld=bfd -pthread -pie -o $@ $< tests/libtls.so, LD tests/tst-tls-pie.so)
 
+$(out)/tests/libtls_gold.so: COMMON += -fuse-ld=gold
+$(out)/tests/libtls_gold.so: $(out)/tests/libtls.o
+	$(makedir)
+	$(call quiet, $(CXX) $(CXXFLAGS) -shared -o $@ $< $(LIBS), LD tests/libtls_gold.so)
+
+$(out)/tests/tst-tls-gold.so: COMMON += -fuse-ld=gold
+$(out)/tests/tst-tls-gold.so: \
+		$(src)/tests/tst-tls.cc \
+		$(out)/tests/libtls_gold.so
+	$(makedir)
+	$(call quiet, cd $(out); $(CXX) $(CXXFLAGS) -D__SHARED_OBJECT__=1 -shared -o $@ $< tests/libtls_gold.so, CXX tests/tst-tls.cc)
+
 boost-lib-dir := $(dir $(shell $(CC) --print-file-name libboost_system.so))
 
 boost-tests := tst-vfs.so tst-libc-locking.so misc-fs-stress.so \