RFR(S): 8170548: VM may crash at startup because StdoutLog/StderrLog logging stream can be badly aligned

Volker Simonis volker.simonis at gmail.com
Thu Dec 1 10:35:52 UTC 2016


can I please have a review and sponsor for the following fix:


Change "8146009: "pure virtual method called" with using new GC
logging mechanism" introduced a sophisticated initialization mechanism
for the logging stream. In order to avoid deconstruction of the
streams before the VM exits, it creates them with a placement new into
statically allocated memory:

static bool initialized;
static char stdoutmem[sizeof(LogStdoutOutput)];
static char stderrmem[sizeof(LogStderrOutput)];

LogStdoutOutput &StdoutLog = reinterpret_cast<LogStdoutOutput&>(stdoutmem);
LogStderrOutput &StderrLog = reinterpret_cast<LogStderrOutput&>(stderrmem);

LogFileStreamInitializer::LogFileStreamInitializer() {
  if (!initialized) {
    ::new (&StdoutLog) LogStdoutOutput();
    ::new (&StderrLog) LogStderrOutput();
    initialized = true;

Unfortunately it is not guaranteed, that the static memory (which is a
char array) is well-aligned for the stream objects. Actually, the C++
standard only defines that it has to be at least 'char' aligned which
is obviously not enough for a stream object.
When building 'slowdebug' on Solaris with SS12u4 we indeed observed
reproducible crashes during VM initialization because of this issue.

The fix is easy - just wrap the character arrays into unions to align
them appropriately.

Thank you and best regards,

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