Kernel dso support for 'dl_iterate_phdr' function

Kernel provides virtual DSO for stack unwinding/exception handlind info for
signal usage case. Stack unwinding routines use 'dl_iterate_phdr' function
for additional DWARF info gathering from DSOs. Patch enables virtual DSO
enumeration via dl_iterate_phdr function.

Signed-off-by: Sergey Melnikov <sergey.melnikov@intel.com>
Change-Id: Ic2882b28f40b456a088bc1e63c50cbfda7e4a102

libc/bionic/dl_iterate_phdr_static.c

@@ -27,39 +27,56 @@
  */
 
 #include <elf.h>
+#include <sys/auxv.h>
 #include <sys/types.h>
 #include <link.h>
 
-/* Dynamic binaries get this from the dynamic linker (system/linker), which
- * we don't pull in for static bins. We also don't have a list of so's to
- * iterate over, since there's really only a single monolithic blob of
- * code/data.
- *
- * All we need to do is to find where the executable is in memory, and grab the
- * phdr and phnum from there.
- */
-
 /* ld provides this to us in the default link script */
-extern void *__executable_start;
+extern void* __executable_start;
 
-int
-dl_iterate_phdr(int (*cb)(struct dl_phdr_info *info, size_t size, void *data),
-                void *data)
-{
-    struct dl_phdr_info dl_info;
-    Elf32_Ehdr *ehdr = (Elf32_Ehdr *) &__executable_start;
-    Elf32_Phdr *phdr = (Elf32_Phdr *)((unsigned long)ehdr + ehdr->e_phoff);
+int dl_iterate_phdr(int (*cb)(struct dl_phdr_info* info, size_t size, void* data), void* data) {
+    Elf32_Ehdr* ehdr = (Elf32_Ehdr*) &__executable_start;
 
-    /* TODO: again, copied from linker.c. Find a better home for this
-     * later. */
+    // TODO: again, copied from linker.c. Find a better home for this later.
     if (ehdr->e_ident[EI_MAG0] != ELFMAG0) return -1;
     if (ehdr->e_ident[EI_MAG1] != ELFMAG1) return -1;
     if (ehdr->e_ident[EI_MAG2] != ELFMAG2) return -1;
     if (ehdr->e_ident[EI_MAG3] != ELFMAG3) return -1;
 
-    dl_info.dlpi_addr = 0;
-    dl_info.dlpi_name = NULL;
-    dl_info.dlpi_phdr = phdr;
-    dl_info.dlpi_phnum = ehdr->e_phnum;
-    return cb(&dl_info, sizeof (struct dl_phdr_info), data);
+    // Dynamic binaries get their dl_iterate_phdr from the dynamic linker, but
+    // static binaries get this. We don't have a list of shared objects to
+    // iterate over, since there's really only a single monolithic blob of
+    // code/data, plus optionally a VDSO.
+
+    struct dl_phdr_info exe_info;
+    exe_info.dlpi_addr = 0;
+    exe_info.dlpi_name = NULL;
+    exe_info.dlpi_phdr = (Elf32_Phdr*) ((unsigned long) ehdr + ehdr->e_phoff);
+    exe_info.dlpi_phnum = ehdr->e_phnum;
+
+#ifdef AT_SYSINFO_EHDR
+    // Try the executable first.
+    int rc = cb(&exe_info, sizeof(exe_info), data);
+    if (rc != 0) {
+        return rc;
+    }
+
+    // Try the VDSO if that didn't work.
+    Elf32_Ehdr* ehdr_vdso = (Elf32_Ehdr*) getauxval(AT_SYSINFO_EHDR);
+    struct dl_phdr_info vdso_info;
+    vdso_info.dlpi_addr = 0;
+    vdso_info.dlpi_name = NULL;
+    vdso_info.dlpi_phdr = (Elf32_Phdr*) ((char*) ehdr_vdso + ehdr_vdso->e_phoff);
+    vdso_info.dlpi_phnum = ehdr_vdso->e_phnum;
+    for (size_t i = 0; i < vdso_info.dlpi_phnum; ++i) {
+        if (vdso_info.dlpi_phdr[i].p_type == PT_LOAD) {
+            vdso_info.dlpi_addr = (Elf32_Addr) ehdr_vdso - vdso_info.dlpi_phdr[i].p_vaddr;
+            break;
+        }
+    }
+    return cb(&vdso_info, sizeof(vdso_info), data);
+#else
+    // There's only the executable to try.
+    return cb(&exe_info, sizeof(exe_info), data);
+#endif
 }

linker/linker.cpp

@@ -1585,6 +1585,28 @@ static bool soinfo_link_image(soinfo* si) {
     return true;
 }
 
+/*
+ * This function add vdso to internal dso list.
+ * It helps to stack unwinding through signal handlers.
+ * Also, it makes bionic more like glibc.
+ */
+static void add_vdso(KernelArgumentBlock& args UNUSED) {
+#ifdef AT_SYSINFO_EHDR
+    Elf32_Ehdr* ehdr_vdso = reinterpret_cast<Elf32_Ehdr*>(args.getauxval(AT_SYSINFO_EHDR));
+
+    soinfo* si = soinfo_alloc("[vdso]");
+    si->phdr = reinterpret_cast<Elf32_Phdr*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff);
+    si->phnum = ehdr_vdso->e_phnum;
+    si->link_map.l_name = si->name;
+    for (size_t i = 0; i < si->phnum; ++i) {
+        if (si->phdr[i].p_type == PT_LOAD) {
+            si->link_map.l_addr = reinterpret_cast<Elf32_Addr>(ehdr_vdso) - si->phdr[i].p_vaddr;
+            break;
+        }
+    }
+#endif
+}
+
 /*
  * This code is called after the linker has linked itself and
  * fixed it's own GOT. It is safe to make references to externs
@@ -1710,6 +1732,8 @@ static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32
         exit(EXIT_FAILURE);
     }
 
+    add_vdso(args);
+
     si->CallPreInitConstructors();
 
     for (size_t i = 0; gLdPreloads[i] != NULL; ++i) {

tests/Android.mk

@@ -74,6 +74,7 @@ test_src_files = \
     regex_test.cpp \
     signal_test.cpp \
     stack_protector_test.cpp \
+    stack_unwinding_test.cpp \
     stdio_test.cpp \
     stdlib_test.cpp \
     string_test.cpp \
@@ -87,6 +88,18 @@ test_dynamic_ldflags = -Wl,--export-dynamic -Wl,-u,DlSymTestFunction
 test_dynamic_src_files = \
     dlfcn_test.cpp \
 
+include $(CLEAR_VARS)
+LOCAL_MODULE := bionic-unit-tests-unwind-test-impl
+LOCAL_CFLAGS += $(test_c_flags) -fexceptions -fnon-call-exceptions
+LOCAL_SRC_FILES := stack_unwinding_test_impl.c
+include $(BUILD_STATIC_LIBRARY)
+
+include $(CLEAR_VARS)
+LOCAL_MODULE := bionic-unit-tests-unwind-test-impl-host
+LOCAL_CFLAGS += $(test_c_flags) -fexceptions -fnon-call-exceptions
+LOCAL_SRC_FILES := stack_unwinding_test_impl.c
+include $(BUILD_HOST_STATIC_LIBRARY)
+
 # Build tests for the device (with bionic's .so). Run with:
 #   adb shell /data/nativetest/bionic-unit-tests/bionic-unit-tests
 include $(CLEAR_VARS)
@@ -97,6 +110,7 @@ LOCAL_LDFLAGS += $(test_dynamic_ldflags)
 LOCAL_SHARED_LIBRARIES += libdl
 LOCAL_SRC_FILES := $(test_src_files) $(test_dynamic_src_files)
 LOCAL_WHOLE_STATIC_LIBRARIES := bionic-unit-tests-clang
+LOCAL_STATIC_LIBRARIES += bionic-unit-tests-unwind-test-impl
 include $(BUILD_NATIVE_TEST)
 
 # Build tests for the device (with bionic's .a). Run with:
@@ -107,7 +121,7 @@ LOCAL_ADDITIONAL_DEPENDENCIES := $(LOCAL_PATH)/Android.mk
 LOCAL_CFLAGS += $(test_c_flags)
 LOCAL_FORCE_STATIC_EXECUTABLE := true
 LOCAL_SRC_FILES := $(test_src_files)
-LOCAL_STATIC_LIBRARIES += libstlport_static libstdc++ libm libc
+LOCAL_STATIC_LIBRARIES += libstlport_static libstdc++ libm libc bionic-unit-tests-unwind-test-impl
 LOCAL_WHOLE_STATIC_LIBRARIES := bionic-unit-tests-clang
 include $(BUILD_NATIVE_TEST)
 
@@ -142,6 +156,7 @@ LOCAL_CFLAGS += $(test_c_flags)
 LOCAL_LDFLAGS += -lpthread -ldl
 LOCAL_LDFLAGS += $(test_dynamic_ldflags)
 LOCAL_SRC_FILES := $(test_src_files) $(test_dynamic_src_files)
+LOCAL_STATIC_LIBRARIES += bionic-unit-tests-unwind-test-impl-host
 include $(BUILD_HOST_NATIVE_TEST)
 endif
 

tests/stack_unwinding_test.cpp

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+/*
+ * Contributed by: Intel Corporation
+ */
+
+#include <gtest/gtest.h>
+
+#if defined(i386) // Only our x86 unwinding is good enough. Switch to libunwind?
+
+extern "C" {
+  void do_test();
+}
+
+// We have to say "DeathTest" here so gtest knows to run this test (which exits)
+// in its own process.
+TEST(stack_unwinding_DeathTest, unwinding_through_signal_frame) {
+  ::testing::FLAGS_gtest_death_test_style = "threadsafe";
+  ASSERT_EXIT(do_test(), ::testing::ExitedWithCode(42), "");
+}
+
+#endif

tests/stack_unwinding_test_impl.c

@@ -0,0 +1,69 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+/*
+ * Contributed by: Intel Corporation
+ */
+
+#include <stdio.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unwind.h>
+
+#define noinline __attribute__((__noinline__))
+#define unused __attribute__((__unused__))
+
+static noinline _Unwind_Reason_Code stop_fn(int a unused,
+    _Unwind_Action action,
+    _Unwind_Exception_Class b unused, struct _Unwind_Exception* c unused,
+    struct _Unwind_Context* d unused, void* e unused) {
+  if ((action & _UA_END_OF_STACK) != 0) {
+    // We reached the end of the stack without executing foo_cleanup. Test failed.
+    abort();
+  }
+  return _URC_NO_REASON;
+}
+
+static void noinline foo_cleanup(char* param unused) {
+  exit(42);
+}
+
+static void noinline do_crash() {
+  char* ptr = NULL;
+  *ptr = 0; // Deliberately cause a SIGSEGV.
+}
+
+static void noinline foo() {
+  char c1 __attribute__((cleanup(foo_cleanup)));
+  do_crash();
+}
+
+// It's SEGSEGV handler. We start forced stack unwinding here.
+// If libgcc don't find dso for signal frame stack unwinding will be finished.
+// libgcc pass to stop_fn _UA_END_OF_STACK flag.
+// Test pass condition: stack unwinding through signal frame and foo1_handler execution.
+static void noinline sigsegv_handler(int param unused) {
+  struct _Unwind_Exception* exception = (struct _Unwind_Exception*) malloc(sizeof(*exception));
+  memset(&exception->exception_class, 0, sizeof(exception->exception_class));
+  exception->exception_cleanup = 0;
+  _Unwind_ForcedUnwind(exception, stop_fn, 0);
+}
+
+void do_test() {
+  signal(SIGSEGV, &sigsegv_handler);
+  foo();
+}