RFR: 8354428: [ubsan] g1BiasedArray.hpp: pointer overflow in address calculation

[Albert Mingkun Yang]

On Mon, 26 May 2025 10:15:01 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this fix for an ubsan error related to pointer under- or overflows when using the biased array helper.
> 
> The fix is, instead of using direct address calculations that can cause these errors, use `uintptr_t` where the overflow behavior is defined in C++. Only convert to pointer at the actual access.
> 
> Testing: gha, tier1

src/hotspot/share/gc/g1/vmStructs_g1.hpp line 51:

> 49:   nonstatic_field(G1HeapRegionTable, _base,             address)              \
> 50:   nonstatic_field(G1HeapRegionTable, _length,           size_t)               \
> 51:   nonstatic_field(G1HeapRegionTable, _biased_base,      size_t)               \

Why `size_t` for `uintptr_t _biased_base;`?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25447#discussion_r2108557618