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minidump: Make the MemoryListStream the caboose once again

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After b10d9118dea4, the MemoryListStream was moved from its preferred
position as the last stream in the file to precede user minidump
streams, in an effort to prevent it from being preempted by a user
minidump stream that specified the memory list stream’s type. A better
solution, which keeps all streams where they want to be, is to put the
MemoryListStream at the end, put user streams before it, and omit user
streams that purport to be a MemoryListStream.

Bug: crashpad:171
Change-Id: I6974fbd4c9ec67284f86c593c553af7adf73601b
Reviewed-on: https://chromium-review.googlesource.com/456823
Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
This commit is contained in:
Mark Mentovai 2017-03-20 08:47:58 -04:00
parent bc5b7b06db
commit 542306626d
1 changed files with 17 additions and 13 deletions
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30
minidump/minidump_file_writer.cc
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@ -146,29 +146,33 @@ void MinidumpFileWriter::InitializeFromSnapshot(
memory_list->AddFromSnapshot(exception_snapshot->ExtraMemory());
}
// The memory list stream should be added last. This keeps the “extra memory”
// at the end so that if the minidump file is truncated, other, more critical
// data is more likely to be preserved. Note that non-“extra” memory regions
// will not have to ride at the end of the file. Thread stack memory, for
// example, exists as a children of threads, and appears alongside them in the
// file.
//
// It would be nice if this followed the user streams, but that would be
// hazardous. See below.
add_stream_result = AddStream(std::move(memory_list));
DCHECK(add_stream_result);
// These user streams must be added last. Otherwise, a user stream with the
// same type as a well-known stream could preempt the well-known stream. As it
// stands now, earlier-discovered user streams can still preempt
// later-discovered ones.
// later-discovered ones. The well-known memory list stream is added after
// these user streams, but only with a check here to avoid adding a user
// stream that would preempt the memory list stream.
for (const auto& module : process_snapshot->Modules()) {
for (const UserMinidumpStream* stream : module->CustomMinidumpStreams()) {
if (stream->stream_type() == kMinidumpStreamTypeMemoryList) {
LOG(WARNING) << "discarding duplicate stream of type "
<< stream->stream_type();
continue;
}
auto user_stream = base::WrapUnique(new MinidumpUserStreamWriter());
user_stream->InitializeFromSnapshot(stream);
AddStream(std::move(user_stream));
}
}
// The memory list stream should be added last. This keeps the “extra memory”
// at the end so that if the minidump file is truncated, other, more critical
// data is more likely to be preserved. Note that non-“extra” memory regions
// will not have to ride at the end of the file. Thread stack memory, for
// example, exists as a children of threads, and appears alongside them in the
// file, despite also being mentioned by the memory list stream.
add_stream_result = AddStream(std::move(memory_list));
DCHECK(add_stream_result);
}
void MinidumpFileWriter::SetTimestamp(time_t timestamp) {