[LSan] Detect dynamic loader by its base address.

[alekseyshl]

Summary

Relanding D38600, which was reverted due to various PPC bot failures.

If it breaks something again, please provide some pointers to broken
bots, not just revert it, otherwise it's very hard to reason what's
wrong with this commit.

Whenever possible (Linux + glibc 2.16+), detect dynamic loader module by
its base address, not by the module name matching. The current name
matching approach fails on some configurations.

[alekseyshl]

• Add back an empty line

lib/lsan/lsan_common.cc

if (m.allocated() && m.tag() != kReachable && m.tag() != kIgnored) {
     if (caller_pc == 0 || (param->skip_linker_allocations &&
                            GetLinker()->containsAddress(caller_pc))) {
       m.set_tag(kReachable);
       param->frontier->push_back(chunk);
     }
   }
 }
 
-// On Linux, handles dynamically allocated TLS blocks by treating all chunks
-// allocated from ld-linux.so as reachable.
+// On Linux, treats all chunks allocated from ld-linux.so as reachable, which
+// covers dynamically allocated TLS blocks, internal dynamic loader's loaded
+// modules accounting etc.
 // Dynamic TLS blocks contain the TLS variables of dynamically loaded modules.
 // They are allocated with a __libc_memalign() call in allocate_and_init()
 // (elf/dl-tls.c). Glibc won't tell us the address ranges occupied by those
 // blocks, but we can make sure they come from our own allocator by intercepting
 // __libc_memalign(). On top of that, there is no easy way to reach them. Their
 // addresses are stored in a dynamically allocated array (the DTV) which is
 // referenced from the static TLS. Unfortunately, we can't just rely on the DTV
 // being reachable from the static TLS, and the dynamic TLS being reachable from

lib/lsan/lsan_common_linux.cc

 #include "sanitizer_common/sanitizer_platform.h"
 #include "lsan_common.h"
 
 #if CAN_SANITIZE_LEAKS && SANITIZER_LINUX
 #include <link.h>
 
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_flags.h"
+#include "sanitizer_common/sanitizer_getauxval.h"
 #include "sanitizer_common/sanitizer_linux.h"
 #include "sanitizer_common/sanitizer_stackdepot.h"
 
 namespace __lsan {
 
 static const char kLinkerName[] = "ld";
 
 static char linker_placeholder[sizeof(LoadedModule)] ALIGNED(64);
 static LoadedModule *linker = nullptr;
 
-static bool IsLinker(const char* full_name) {
-  return LibraryNameIs(full_name, kLinkerName);
+static bool IsLinker(const LoadedModule& module) {
+#if SANITIZER_USE_GETAUXVAL
+  return module.base_address() == getauxval(AT_BASE);
+#else
+  return LibraryNameIs(module.full_name(), kLinkerName);
+#endif  // SANITIZER_USE_GETAUXVAL
 }
 
 __attribute__((tls_model("initial-exec")))
 THREADLOCAL int disable_counter;
 bool DisabledInThisThread() { return disable_counter > 0; }
 void DisableInThisThread() { disable_counter++; }
 void EnableInThisThread() {
   if (disable_counter == 0) {
     DisableCounterUnderflow();
   }
   disable_counter--;
 }
 
 void InitializePlatformSpecificModules() {
   ListOfModules modules;
   modules.init();
   for (LoadedModule &module : modules) {
-    if (!IsLinker(module.full_name())) continue;
+    if (!IsLinker(module))
+      continue;
     if (linker == nullptr) {
       linker = reinterpret_cast<LoadedModule *>(linker_placeholder);
       *linker = module;
       module = LoadedModule();
     } else {
       VReport(1, "LeakSanitizer: Multiple modules match \"%s\". "
-              "TLS will not be handled correctly.\n", kLinkerName);
+              "TLS and other allocations originating from linker might be "
+              "falsely reported as leaks.\n", kLinkerName);
       linker->clear();
       linker = nullptr;
       return;
     }
   }
   if (linker == nullptr) {
-    VReport(1, "LeakSanitizer: Dynamic linker not found. "
-               "TLS will not be handled correctly.\n");
+    VReport(1, "LeakSanitizer: Dynamic linker not found. TLS and other "
+               "allocations originating from linker might be falsely reported "
+                "as leaks.\n");
   }
 }
 
 static int ProcessGlobalRegionsCallback(struct dl_phdr_info *info, size_t size,
                                         void *data) {
   Frontier *frontier = reinterpret_cast<Frontier *>(data);
   for (uptr j = 0; j < info->dlpi_phnum; j++) {
     const ElfW(Phdr) *phdr = &(info->dlpi_phdr[j]);

lib/sanitizer_common/sanitizer_getauxval.h

+//===-- sanitizer_getauxval.h -----------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Common getauxval() guards and definitions.
+// getauxval() is not defined until glbc version 2.16.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SANITIZER_GETAUXVAL_H
+#define SANITIZER_GETAUXVAL_H
+
+#include "sanitizer_platform.h"
+
+#if SANITIZER_LINUX
+
+#include <features.h>
+
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(x, y) 0
+#endif
+
+#if __GLIBC_PREREQ(2, 16)
+# define SANITIZER_USE_GETAUXVAL 1
+#else
+# define SANITIZER_USE_GETAUXVAL 0
+#endif
+
+#if SANITIZER_USE_GETAUXVAL
+#include <sys/auxv.h>
+#endif
+
+#endif // SANITIZER_LINUX
+
+#endif // SANITIZER_GETAUXVAL_H

lib/sanitizer_common/sanitizer_linux.cc

 //===----------------------------------------------------------------------===//
 
 #include "sanitizer_platform.h"
 
 #if SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD
 
 #include "sanitizer_common.h"
 #include "sanitizer_flags.h"
+#include "sanitizer_getauxval.h"
 #include "sanitizer_internal_defs.h"
 #include "sanitizer_libc.h"
 #include "sanitizer_linux.h"
 #include "sanitizer_mutex.h"
 #include "sanitizer_placement_new.h"
 #include "sanitizer_procmaps.h"
 #include "sanitizer_stacktrace.h"
 #include "sanitizer_symbolizer.h"

 #include <sys/sysctl.h>
 extern char **environ;  // provided by crt1
 #endif                  // SANITIZER_NETBSD
 
 #if !SANITIZER_ANDROID
 #include <sys/signal.h>
 #endif
 
-#ifndef __GLIBC_PREREQ
-#define __GLIBC_PREREQ(x, y) 0
-#endif
-
-#if SANITIZER_LINUX && __GLIBC_PREREQ(2, 16)
-# define SANITIZER_USE_GETAUXVAL 1
-#else
-# define SANITIZER_USE_GETAUXVAL 0
-#endif
-
-#if SANITIZER_USE_GETAUXVAL
-#include <sys/auxv.h>
-#endif
-
 #if SANITIZER_LINUX
 // <linux/time.h>
 struct kernel_timeval {
   long tv_sec;
   long tv_usec;
 };
 
 // <linux/futex.h> is broken on some linux distributions.