RFR: JDK-8296995: ostream should handle snprintf(3) errors in release builds [v3]

[Martin Doerr]

On Wed, 7 Dec 2022 14:03:11 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> Small fix for a very unlikely problem. 
>> 
>> All streams in ostream.hpp end up using `os::snprintf()`, which uses `::vsnprintf()`. `vsnprintf(3)`can fail and return -1. 
>> 
>> The chance for this to happen is small. snprintf errors are usually encoding errors though not always (see third example at https://stackoverflow.com/questions/65334245/what-is-an-encoding-error-for-sprintf-that-should-return-1). I found "%ls" in one place in windows coding, so I am not sure we can always exclude the possibility of wide strings being used in our code base, or that of printing with outside-provided format strings.
>> 
>> In case of an error, we assert in debug builds but don't handle it in release. There, this situation gets misdiagnosed later as a buffer overflow because we cast the signedness of the result away (see `outputStream::do_vsnprintf()`). 
>> 
>> ---
>> 
>> The patch is trivial. The most exciting thing is the gtest, I guess.
>> 
>> In release builds, we now treat this condition as an empty string write. I considered printing a clear marker into the stream instead, e.g. "ENCODING ERROR", but ultimately did not do it.
>
> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
> 
>   feedback martin

Thanks for the update! LGTM. Please update the test's Copyright header as requested by Matthias.

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Marked as reviewed by mdoerr (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11160