Fix memory corruption in base_unittests in some configuration.

base/trace_event/process_memory_dump.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/process_memory_dump.h"
 
 #include <errno.h>
 
 #include <vector>
 
 #include "base/memory/ptr_util.h"
 #include "base/process/process_metrics.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/heap_profiler_heap_dump_writer.h"
 #include "base/trace_event/memory_infra_background_whitelist.h"
 #include "base/trace_event/process_memory_totals.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "build/build_config.h"
 
 #if defined(OS_IOS)
-#include <sys/sysctl.h>
+#include <mach/vm_page_size.h>
 #endif
 
 #if defined(OS_POSIX)
 #include <sys/mman.h>
 #endif
 
 #if defined(OS_WIN)
 #include <Psapi.h>
 #endif
 
@@ skipping 18 matching lines @@
 }  // namespace
 
 // static
 bool ProcessMemoryDump::is_black_hole_non_fatal_for_testing_ = false;
 
 #if defined(COUNT_RESIDENT_BYTES_SUPPORTED)
 // static
 size_t ProcessMemoryDump::GetSystemPageSize() {
 #if defined(OS_IOS)
   // On iOS, getpagesize() returns the user page sizes, but for allocating
-  // arrays for mincore(), kernel page sizes is needed. sysctlbyname() should
-  // be used for this. Refer to crbug.com/542671 and Apple rdar://23651782
-  int pagesize;
-  size_t pagesize_len;
-  int status = sysctlbyname("vm.pagesize", NULL, &pagesize_len, nullptr, 0);
-  if (!status && pagesize_len == sizeof(pagesize)) {
-    if (!sysctlbyname("vm.pagesize", &pagesize, &pagesize_len, nullptr, 0))
-      return pagesize;
-  }
-  LOG(ERROR) << "sysctlbyname(\"vm.pagesize\") failed.";
-  // Falls back to getpagesize() although it may be wrong in certain cases.
+  // arrays for mincore(), kernel page sizes is needed. Use vm_kernel_page_size
+  // as recommended by Apple, https://forums.developer.apple.com/thread/47532/.
+  // Refer to http://crbug.com/542671 and Apple rdar://23651782
+  return vm_kernel_page_size;
+#else
+  return base::GetPageSize();
 #endif  // defined(OS_IOS)
-  return base::GetPageSize();

[Primiano Tucci (use gerrit), 2016/09/26 14:24:05]

I liked this the old way, i.e.
#if special case
...
return x
#endif
return x // general case

instead of the #else,
but not a huge deal.

[sdefresne, 2016/09/26 14:44:36]

Won't this cause a warning by the compiler about unreachable code? And returning
base::GetPageSize() here on iOS is incorrect. I'd prefer to make it clear that
it should have a different implementation on iOS.

 }
 
 // static
 size_t ProcessMemoryDump::CountResidentBytes(void* start_address,
                                              size_t mapped_size) {
   const size_t page_size = GetSystemPageSize();
   const uintptr_t start_pointer = reinterpret_cast<uintptr_t>(start_address);
   DCHECK_EQ(0u, start_pointer % page_size);
 
   size_t offset = 0;
@@ skipping 281 matching lines @@
 
 MemoryAllocatorDump* ProcessMemoryDump::GetBlackHoleMad() {
   DCHECK(is_black_hole_non_fatal_for_testing_);
   if (!black_hole_mad_)
     black_hole_mad_.reset(new MemoryAllocatorDump("discarded", this));
   return black_hole_mad_.get();
 }
 
 }  // namespace trace_event
 }  // namespace base