Added test for ifunc support in dynamic linker.

ifuncs now work in i386 and x86_64 when called in the same library as
well as in a different library.

Bug:6657325
Change-Id: Ic0c48b1b0a76cb90f36c20c79f68294cc3fd44a1

libc/include/elf.h

@@ -69,14 +69,17 @@ typedef struct {
 
 #define PT_GNU_RELRO 0x6474e552
 
-#define STB_LOOS   10
+#define STB_LOOS      10
-#define STB_HIOS   12
+#define STB_HIOS      12
-#define STB_LOPROC 13
+#define STB_LOPROC    13
-#define STB_HIPROC 15
+#define STB_HIPROC    15
 
-#define STT_LOOS   10
+#define STT_GNU_IFUNC 10
-#define STT_HIOS   12
+#define STT_LOOS      10
-#define STT_LOPROC 13
+#define STT_HIOS      12
-#define STT_HIPROC 15
+#define STT_LOPROC    13
+#define STT_HIPROC    15
+
+#define R_386_IRELATIVE  42
 
 #endif /* _ELF_H */

linker/linker.cpp

@@ -476,6 +476,29 @@ static ElfW(Sym)* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name,
   return NULL;
 }
 
+static void resolve_ifunc_symbols(soinfo* si) {
+
+  phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias);
+
+  TRACE_TYPE(IFUNC, "CHECKING FOR IFUNCS AND PERFORMING SYMBOL UPDATES");
+
+  for (size_t i = 0; i < si->nchain; ++i) {
+    ElfW(Sym)* s = &si->symtab[i];
+    if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+      // The address of the ifunc in the symbol table is the address of the
+      // function that chooses the function to which the ifunc will refer.
+      // In order to return the proper value, we run the choosing function
+      // in the linker and then return its result (minus the base offset).
+      TRACE_TYPE(IFUNC, "FOUND IFUNC");
+      ElfW(Addr) (*ifunc_ptr)();
+      ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + si->base);
+      s->st_value = (ifunc_ptr() - si->base);
+      TRACE_TYPE(IFUNC, "NEW VALUE IS %p", (void*)s->st_value);
+    }
+  }
+  phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias);
+}
+
 static unsigned elfhash(const char* _name) {
     const unsigned char* name = reinterpret_cast<const unsigned char*>(_name);
     unsigned h = 0, g;
@@ -790,6 +813,10 @@ static soinfo* load_library(const char* name, int dlflags, const android_dlextin
       return NULL;
     }
 
+    // if the library has any ifuncs, we will need to resolve them so that dlsym
+    // can handle them properly
+    resolve_ifunc_symbols(si);
+
     return si;
 }
 
@@ -903,6 +930,53 @@ void do_dlclose(soinfo* si) {
   protect_data(PROT_READ);
 }
 
+// ifuncs are only defined for x86
+#if defined(__i386__)
+static void soinfo_ifunc_relocate(soinfo* si, ElfW(Rel)* rel, unsigned count, soinfo* needed[]) {
+  for (size_t idx = 0; idx < count; ++idx, ++rel) {
+    ElfW(Sym)* s;
+    soinfo* lsi;
+    unsigned type = ELFW(R_TYPE)(rel->r_info);
+    unsigned sym = ELFW(R_SYM)(rel->r_info);
+    ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rel->r_offset + si->load_bias);
+    ElfW(Addr) sym_addr = 0;
+    const char* sym_name = NULL;
+    sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
+    s = soinfo_do_lookup(si, sym_name, &lsi, needed);
+
+    if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC && type == R_386_JMP_SLOT) {
+      TRACE("IFUNC RELOCATION, PASS 2: %p",  (void*)(sym_addr));
+      ElfW(Addr) (*ifunc_ptr)();
+      ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + si->base);
+      *reinterpret_cast<ElfW(Addr)*>(reloc) = ifunc_ptr();
+    }
+  }
+}
+#endif
+
+#if defined(__x86_64__)
+static void soinfo_ifunc_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo* needed[]) {
+  for (size_t idx = 0; idx < count; ++idx, ++rela) {
+    ElfW(Sym)* s;
+    soinfo* lsi;
+    unsigned type = ELFW(R_TYPE)(rela->r_info);
+    unsigned sym = ELFW(R_SYM)(rela->r_info);
+    ElfW(Addr) reloc = static_cast<ElfW(Addr)>(rela->r_offset + si->load_bias);
+    ElfW(Addr) sym_addr = 0;
+    const char* sym_name = NULL;
+    sym_name = reinterpret_cast<const char*>(si->strtab + si->symtab[sym].st_name);
+    s = soinfo_do_lookup(si, sym_name, &lsi, needed);
+
+    if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC && type == R_X86_64_JUMP_SLOT) {
+      TRACE("IFUNC RELOCATION, PASS 2: %p",  (void*)(sym_addr + rela->r_addend));
+      ElfW(Addr) (*ifunc_ptr)();
+      ifunc_ptr = reinterpret_cast<ElfW(Addr)(*)()>(s->st_value + si->base);
+      *reinterpret_cast<ElfW(Addr)*>(reloc) = ifunc_ptr();
+    }
+  }
+}
+#endif
+
 #if defined(USE_RELA)
 static int soinfo_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo* needed[]) {
   ElfW(Sym)* s;
@@ -1114,7 +1188,11 @@ static int soinfo_relocate(soinfo* si, ElfW(Rela)* rela, unsigned count, soinfo*
       MARK(rela->r_offset);
       TRACE_TYPE(RELO, "RELO JMP_SLOT %08zx <- %08zx %s", static_cast<size_t>(reloc),
                  static_cast<size_t>(sym_addr + rela->r_addend), sym_name);
-      *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
+      if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+        si->set_has_ifuncs(true);
+      } else {
+        *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr + rela->r_addend;
+      }
       break;
     case R_X86_64_GLOB_DAT:
       count_relocation(kRelocAbsolute);
@@ -1293,7 +1371,11 @@ static int soinfo_relocate(soinfo* si, ElfW(Rel)* rel, unsigned count, soinfo* n
             count_relocation(kRelocAbsolute);
             MARK(rel->r_offset);
             TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name);
-            *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
+            if (ELF_ST_TYPE(s->st_info) == STT_GNU_IFUNC) {
+              si->set_has_ifuncs(true);
+            } else {
+              *reinterpret_cast<ElfW(Addr)*>(reloc) = sym_addr;
+            }
             break;
         case R_386_GLOB_DAT:
             count_relocation(kRelocAbsolute);
@@ -1553,6 +1635,14 @@ void soinfo::set_st_ino(ino_t ino) {
   st_ino = ino;
 }
 
+void soinfo::set_has_ifuncs(bool ifuncs) {
+  if ((this->flags & FLAG_NEW_SOINFO) == 0) {
+    return;
+  }
+
+  has_ifuncs = ifuncs;
+}
+
 dev_t soinfo::get_st_dev() {
   if ((this->flags & FLAG_NEW_SOINFO) == 0) {
     return 0;
@@ -1569,6 +1659,14 @@ ino_t soinfo::get_st_ino() {
   return st_ino;
 }
 
+bool soinfo::get_has_ifuncs() {
+  if ((this->flags & FLAG_NEW_SOINFO) == 0) {
+    return false;
+  }
+
+  return has_ifuncs;
+}
+
 // This is a return on get_children() in case
 // 'this->flags' does not have FLAG_NEW_SOINFO set.
 static soinfo::soinfo_list_t g_empty_list;
@@ -1953,6 +2051,18 @@ static bool soinfo_link_image(soinfo* si, const android_dlextinfo* extinfo) {
     }
 #endif
 
+    // if there are ifuncs, we need to do an additional relocation pass.
+    // they cannot be resolved until the rest of the relocations are done
+    // because we need to call the resolution function which may be waiting
+    // on relocations.
+    if(si->get_has_ifuncs()) {
+#if defined(__i386__)
+      soinfo_ifunc_relocate(si, si->plt_rel, si->plt_rel_count, needed);
+#elif defined(__x86_64__)
+      soinfo_ifunc_relocate(si, si->plt_rela, si->plt_rela_count, needed);
+#endif
+    }
+
 #if defined(__mips__)
     if (!mips_relocate_got(si, needed)) {
         return false;

linker/linker.h

@@ -204,8 +204,12 @@ struct soinfo {
 
   void set_st_dev(dev_t st_dev);
   void set_st_ino(ino_t st_ino);
+  void set_has_ifuncs(bool ifunc);
   ino_t get_st_ino();
   dev_t get_st_dev();
+  bool get_has_ifuncs();
+
+
 
   soinfo_list_t& get_children();
 
@@ -218,6 +222,8 @@ struct soinfo {
   // when FLAG_NEW_SOINFO is set in this->flags.
   unsigned int version;
 
+  bool has_ifuncs;
+
   dev_t st_dev;
   ino_t st_ino;
 

linker/linker_debug.h

@@ -42,6 +42,7 @@
 #define TRACE_DEBUG          1
 #define DO_TRACE_LOOKUP      1
 #define DO_TRACE_RELO        1
+#define DO_TRACE_IFUNC       1
 #define TIMING               0
 #define STATS                0
 #define COUNT_PAGES          0

tests/dlfcn_test.cpp

@@ -106,6 +106,39 @@ TEST(dlfcn, dlopen_noload) {
   ASSERT_EQ(0, dlclose(handle2));
 }
 
+// ifuncs are only supported on intel for now
+#if defined(__i386__) || defined(__x86_64__)
+TEST(dlfcn, ifunc) {
+  const char* (*foo_ptr)();
+  const char* (*foo_library_ptr)();
+
+  // ifunc's choice depends on whether IFUNC_CHOICE has a value
+  // first check the set case
+  setenv("IFUNC_CHOICE", "set", 1);
+  void* handle = dlopen("libtest_ifunc.so", RTLD_NOW);
+  ASSERT_TRUE(handle != NULL);
+  *(void **)(&foo_ptr) = dlsym(handle, "foo");
+  *(void **)(&foo_library_ptr) = dlsym(handle, "foo_library");
+  ASSERT_TRUE(foo_ptr != NULL);
+  ASSERT_TRUE(foo_library_ptr != NULL);
+  ASSERT_EQ(strncmp("set", (*foo_ptr)(), 3), 0);
+  ASSERT_EQ(strncmp("set", (*foo_library_ptr)(), 3), 0);
+  dlclose(handle);
+
+  // then check the unset case
+  unsetenv("IFUNC_CHOICE");
+  handle = dlopen("libtest_ifunc.so", RTLD_NOW);
+  ASSERT_TRUE(handle != NULL);
+  *(void **)(&foo_ptr) = dlsym(handle, "foo");
+  *(void **)(&foo_library_ptr) = dlsym(handle, "foo_library");
+  ASSERT_TRUE(foo_ptr != NULL);
+  ASSERT_TRUE(foo_library_ptr != NULL);
+  ASSERT_EQ(strncmp("unset", (*foo_ptr)(), 5), 0);
+  ASSERT_EQ(strncmp("unset", (*foo_library_ptr)(), 3), 0);
+  dlclose(handle);
+}
+#endif
+
 TEST(dlfcn, dlopen_failure) {
   void* self = dlopen("/does/not/exist", RTLD_NOW);
   ASSERT_TRUE(self == NULL);

tests/libs/Android.mk

@@ -114,6 +114,20 @@ build_type := target
 build_target := SHARED_LIBRARY
 include $(TEST_PATH)/Android.build.mk
 
+# -----------------------------------------------------------------------------
+# Library used by ifunc tests
+# -----------------------------------------------------------------------------
+ifeq ($(TARGET_ARCH),$(filter $(TARGET_ARCH),x86 x86_64))
+    libtest_ifunc_src_files := \
+        dlopen_testlib_ifunc.c
+
+    LOCAL_SDK_VERSION := current
+    module := libtest_ifunc
+    build_type := target
+    build_target := SHARED_LIBRARY
+    include $(TEST_PATH)/Android.build.mk
+endif
+
 # -----------------------------------------------------------------------------
 # Library used to test local symbol lookup
 # -----------------------------------------------------------------------------

tests/libs/dlopen_testlib_ifunc.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+const char* foo() __attribute__ ((ifunc ("foo_ifunc")));
+
+const char* f1() {
+  return "unset";
+}
+
+const char* f2() {
+  return "set";
+}
+
+void* foo_ifunc() {
+   char* choice = getenv("IFUNC_CHOICE");
+   return choice == NULL ? f1 : f2;
+}
+
+const char* foo_library() {
+   return foo();
+}