RFR: 8328306: AArch64: MacOS lazy JIT "write xor execute" switching [v3]

[Dean Long]

On Mon, 18 Aug 2025 15:49:15 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> src/hotspot/os_cpu/bsd_aarch64/os_bsd_aarch64.cpp line 249:
>> 
>>> 247:     // If we got a SIGBUS because we tried to write into the code
>>> 248:     // cache, try enabling WXWrite mode.
>>> 249:     if (sig == SIGBUS && pc != info->si_addr && CodeCache::contains(info->si_addr) && !CodeCache::contains(pc)) {
>> 
>> Only the hotspot code should write into the code cache, right? A more secure alternative would be then to use `os::address_is_in_vm()`. That compares against the text segment of the libjvm. Prevents accidental misdiagnosis of writes from anywhere (including possibly deliberate ones).
>
>> Only the hotspot code should write into the code cache, right? A more secure alternative would be then to use `os::address_is_in_vm()`. That compares against the text segment of the libjvm. Prevents accidental misdiagnosis of writes from anywhere (including possibly deliberate ones).
> 
> True, but is `dladdr(3)` safe to call from a sighandler on BSD? I don't know, but I wouldn't have thought so.

To make it safe to call from a signal handler, we could take a snapshot of the boundaries during startup, something like what os::get_loaded_modules_info() does.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26562#discussion_r2283746055