RFR: 8271003: hs_err improvement: handle CLASSPATH env setting longer than O_BUFLEN

[Thomas Stuefe]

On Mon, 2 Aug 2021 07:02:35 GMT, David Holmes <dholmes at openjdk.org> wrote:

> `outputStream::do_vsnprintf` already states that it uses the buffer "if necessary". In the two highlighted cases there is no need to use the buffer, so I would argue that we should just modify the existing `outputStream::do_vsnprintf` logic to not truncate in these two cases as it is not necessary.

I think we already do almost that.

https://github.com/openjdk/jdk/blob/95f0fd6c4dfaea9c3e065485dd201decf2be98ba/src/hotspot/share/utilities/ostream.cpp#L94-L104

Only thing, for print_cr() we still use the scratch buffer since we need to append \n. That could be done smarter.

Beyond that, I think the O_BUFLEN thing is seriously annoying and I would like to have a better solution. One where we start with a preallocated buffer as we do now, but expand it dynamically (using raw ::malloc()) if necessary. That should still be reasonably safe.

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PR: https://git.openjdk.java.net/jdk/pull/4947