commit a535d3ca6557ced23d8f87d1b3f6b85bd2e8e068
author Dan Albert <danalbert@google.com> Thu Feb 14 16:19:59 2019 -0800
committer Dan Albert <danalbert@google.com> Wed Feb 20 12:44:19 2019 -0800
tree b8217b419ef1d9a50eed205878b8a70875b06d2d
parent 11dff3e91c6afd68e4e6c46f8249d10f07f307a7

Make static ifunc resolvers optional.

Gold isn't emitting these symbols, so we don't necessarily have the
support for them (gold is still the default for most architectures in
the NDK).

Test: bionic static unit tests
Bug: None
Change-Id: Ifc360cb6c26571fb3f0309adb0faf0af7ee5b36f

libc/bionic/libc_init_static.cpp

diff --git a/libc/bionic/libc_init_static.cpp b/libc/bionic/libc_init_static.cpp
index 3219239..41f100d 100644
--- a/libc/bionic/libc_init_static.cpp
+++ b/libc/bionic/libc_init_static.cpp
@@ -67,9 +67,20 @@
 }
 
 #if defined(__aarch64__) || defined(__x86_64__)
-extern __LIBC_HIDDEN__ ElfW(Rela) __rela_iplt_start[], __rela_iplt_end[];
+extern __LIBC_HIDDEN__ __attribute__((weak)) ElfW(Rela) __rela_iplt_start[], __rela_iplt_end[];
 
 static void call_ifunc_resolvers() {
+  if (__rela_iplt_start == nullptr || __rela_iplt_end == nullptr) {
+    // These symbols are not emitted by gold. Gold has code to do so, but for
+    // whatever reason it is not being run. In these cases ifuncs cannot be
+    // resolved, so we do not support using ifuncs in static executables linked
+    // with gold.
+    //
+    // Since they are weak, they will be non-null when linked with bfd/lld and
+    // null when linked with gold.
+    return;
+  }
+
   typedef ElfW(Addr) (*ifunc_resolver_t)(void);
   for (ElfW(Rela) *r = __rela_iplt_start; r != __rela_iplt_end; ++r) {
     ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);
@@ -78,9 +89,20 @@
   }
 }
 #else
-extern __LIBC_HIDDEN__ ElfW(Rel) __rel_iplt_start[], __rel_iplt_end[];
+extern __LIBC_HIDDEN__ __attribute__((weak)) ElfW(Rel) __rel_iplt_start[], __rel_iplt_end[];
 
 static void call_ifunc_resolvers() {
+  if (__rel_iplt_start == nullptr || __rel_iplt_end == nullptr) {
+    // These symbols are not emitted by gold. Gold has code to do so, but for
+    // whatever reason it is not being run. In these cases ifuncs cannot be
+    // resolved, so we do not support using ifuncs in static executables linked
+    // with gold.
+    //
+    // Since they are weak, they will be non-null when linked with bfd/lld and
+    // null when linked with gold.
+    return;
+  }
+
   typedef ElfW(Addr) (*ifunc_resolver_t)(void);
   for (ElfW(Rel) *r = __rel_iplt_start; r != __rel_iplt_end; ++r) {
     ElfW(Addr)* offset = reinterpret_cast<ElfW(Addr)*>(r->r_offset);