RFR: 8340923: The class LogSelection copies uninitialized memory

[Matthias Baesken]

On Wed, 25 Sep 2024 13:43:47 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> The class LogSelection's custom constructor does not initialize the whole _tags array but is lacking a custom copy constructor and assignment operator. This means that any copy will copy uninitialized memory, which is undefined behavior. UBSAN has seen this happen, as reported by Matthias Baesken.
> 
> For some surrounding context: Unified Logging uses a statically defined array size (`LogTag::MaxTag`) but uses the `LogTag::__NO_TAG` to signify the end of the array. Think "NULL-terminated string but log tags".
> 
> We fill the whole array to avoid this issue. Specifically, we filll the remainder of the array with `LogTag::__NO_TAG`.

After fixing the mentioned compile issues, and building with ubsan enabled,  I can confirm that the mentioned ubsan errors  from https://bugs.openjdk.org/browse/JDK-8333090  (seen when running the HS cds/appcds  tests)  are gone.

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PR Comment: https://git.openjdk.org/jdk/pull/21185#issuecomment-2374278446