RFR: 8346157: [Ubsan]: runtime error: pointer index expression with base 0x000000001000 overflowed to 0xfffffffffffffff0 [v3]

[Thomas Stuefe]

On Mon, 6 Jan 2025 06:35:17 GMT, Amit Kumar <amitkumar at openjdk.org> wrote:

>> Fixes ubsan warning in mallocTracker.cpp
>
> Amit Kumar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   cap 0 at end and early bailout

src/hotspot/share/nmt/mallocTracker.cpp line 234:

> 232:   address addr = (address)p;
> 233: 
> 234:   if (p2u(addr) < MAX2(os::vm_min_address(), (size_t)16 * 0x100000 /* 16 MB */)) {

Use "M" instead of 0x100000?

src/hotspot/share/nmt/mallocTracker.cpp line 252:

> 250:     uintptr_t end = (here > (0x1000 + sizeof(MallocHeader)))
> 251:                       ? here - (0x1000 + sizeof(MallocHeader)) // stop searching after 4k
> 252:                       : 0;

`here` will always be > 0, overflowed or not. You need to check the decrement amount before decrementing. With "capping end" I meant setting it at or above the decrement amount, e.g.

end = MAX2(smallest_possible_alignment, here - (0x1000 + sizeof(MallocHeader))

(sorry if I wasn't clear)

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PR Review Comment: https://git.openjdk.org/jdk/pull/22885#discussion_r1903823142
PR Review Comment: https://git.openjdk.org/jdk/pull/22885#discussion_r1903830487