10.6 SDK compatibility

compat/mac/mach-o/getsect.cc

+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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 <mach-o/getsect.h>
+
+// This is only necessary when building code that might run on systems earlier
+// than 10.7. When building for 10.7 or later, getsectiondata() and
+// getsegmentdata() are always present in libmacho and made available through
+// libSystem. When building for earlier systems, custom definitions of
+// these functions are needed.
+//
+// This file checks the deployment target instead of the SDK. The deployment
+// target is correct because it identifies the earliest possible system that
+// the code being compiled is expected to run on.
+
+#if MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7
+
+#include <dlfcn.h>
+#include <stddef.h>
+
+#include "third_party/apple_cctools/cctools/include/mach-o/getsect.h"
+
+namespace {
+
+// Returns a dlopen() handle to the same library that provides the
+// getsectbyname() function. getsectbyname() is always present in libmacho.
+// getsectiondata() and getsegmentdata() are not always present, but when they
+// are, they’re in the same library as getsectbyname(). If the library cannot
+// be found or a handle to it cannot be returned, returns NULL.
+void* SystemLibMachOHandle() {
+  Dl_info info;
+  if (!dladdr(reinterpret_cast<void*>(getsectbyname), &info)) {
+    return NULL;
+  }
+  return dlopen(info.dli_fname, RTLD_LAZY | RTLD_LOCAL);
+}
+
+// Returns a function pointer to a function in libmacho based on a lookup of
+// that function by symbol name. Returns NULL if libmacho cannot be found or
+// opened, or if the named symbol cannot be found in libmacho.
+void* LookUpSystemLibMachOSymbol(const char* symbol) {
+  static void* dl_handle = SystemLibMachOHandle();
+  if (!dl_handle) {
+    return NULL;
+  }
+  return dlsym(dl_handle, symbol);
+}
+
+#ifndef __LP64__
+typedef mach_header MachHeader;
+#else
+typedef mach_header_64 MachHeader;
+#endif
+
+typedef uint8_t*(*GetSectionDataType)(
+    const MachHeader*, const char*, const char*, unsigned long*);
+typedef uint8_t*(*GetSegmentDataType)(
+    const MachHeader*, const char*, unsigned long*);
+
+}  // namespace
+
+extern "C" {
+
+// These implementations look up their functions in libmacho at run time. If
+// the system libmacho provides these functions as it normally does on Mac OS X
+// 10.7 and later, the system’s versions are used directly. Otherwise, the
+// versions in third_party/apple_cctools are used, which are actually just
+// copies of the system’s functions.
+
+uint8_t* getsectiondata(const MachHeader* mhp,
+                        const char* segname,
+                        const char* sectname,
+                        unsigned long* size) {
+  static GetSectionDataType system_getsectiondata =
+      reinterpret_cast<GetSectionDataType>(
+          LookUpSystemLibMachOSymbol("getsectiondata"));
+  if (system_getsectiondata) {
+    return system_getsectiondata(mhp, segname, sectname, size);
+  }
+  return crashpad_getsectiondata(mhp, segname, sectname, size);
+}
+
+uint8_t* getsegmentdata(
+    const MachHeader* mhp, const char* segname, unsigned long* size) {
+  static GetSegmentDataType system_getsegmentdata =
+      reinterpret_cast<GetSegmentDataType>(
+          LookUpSystemLibMachOSymbol("getsegmentdata"));
+  if (system_getsegmentdata) {
+    return system_getsegmentdata(mhp, segname, size);
+  }
+  return crashpad_getsegmentdata(mhp, segname, size);
+}
+
+}  // extern "C"
+
+#endif  // MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7