RFR: JDK-8298908: Instrument Metaspace for ASan [v2]

[Ioi Lam]

On Mon, 9 Jan 2023 15:48:48 GMT, Justin King <jcking at openjdk.org> wrote:

>> I like this, but would compilers not complain about unused statements?
>
> I don't believe so, at least not based on current options. Other projects use similar tricks, like ABSL_DCHECK from Abseil which short circuits expressions when in non-debug builds causing the code to be unreachable and stripped. If it does, we can always just remove the if statement part and have it evaluate anyway. Most compilers should realize that the statements are unused and should be pruned.

The macros `ASAN_POISON_MEMORY_REGION` and `ASAN_UNPOISON_MEMORY_REGION` are already defined in [sanitizer/asan_interface.h](https://opensource.apple.com/source/clang/clang-700.1.81/src/projects/compiler-rt/include/sanitizer/asan_interface.h.auto.html), but we redefine them here. 

Since ASan is going to be an obscured feature for many HotSpot developers, I don't think we should make it more obscured.

I think it's better to declare our own macros that call into the existing macros. Maybe something like 
`_ASAN_POISON_MEMORY_REGION`. The comments should be improved to say why we do this (to prevent people that don't use ASan from breaking ASan).

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PR: https://git.openjdk.org/jdk/pull/11702