RFR: 8340923: The class LogSelection copies uninitialized memory [v2]

[Abdelhak Zaaim]

On Wed, 25 Sep 2024 14:53:49 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`.
>
> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixes

I suggest using std::fill(_tags + _ntags, _tags + LogTag::MaxTags, LogTag::__NO_TAG); instead of the manual loop. Its cleaner, easier to read  and takes advantage of the standard library.

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Changes requested by abdelhak-zaaim at github.com (no known OpenJDK username).

PR Review: https://git.openjdk.org/jdk/pull/21185#pullrequestreview-2328922263