## Background

When I was running a jtreg test with
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make test TEST="test/jdk/java/lang/invoke/TestCatchExceptionWithVarargs.java" CONF=fast
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I got some VM warnings which just told me to increase O_BUFLEN in ostream.hpp.
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Running test 'jtreg:test/jdk/java/lang/invoke/TestCatchExceptionWithVarargs.java'
[2019-09-14 16:07:55,752] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,758] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,763] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,769] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,777] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,785] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,796] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,803] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,808] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
[2019-09-14 16:07:55,815] Agent[1]: stderr: OpenJDK 64-Bit Server VM warning: increase O_BUFLEN in ostream.hpp -- output truncated
...
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But the debug info didn't tell us the proper value of O_BUFLEN needed by the output.