RFR: 8361043: [ubsan] os::print_hex_dump runtime error: applying non-zero offset 8 to null pointer

[Lutz Schmidt]

On Mon, 30 Jun 2025 07:49:45 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> When running jtreg test
> runtime/cds/DeterministicDump
> with ubsan-enabled binaries (opt) on macOS aarch64, the following issue is reported :
> 
> 
> /jdk/src/hotspot/share/runtime/os.cpp:1045:15: runtime error: applying non-zero offset 8 to null pointer
>     #0 0x106156ad4 in os::print_hex_dump(outputStream*, unsigned char const*, unsigned char const*, int, bool, int, unsigned char const*, unsigned char const*) os.cpp:1045
>     #1 0x10524685c in ArchiveBuilder::CDSMapLogger::log(ArchiveBuilder*, FileMapInfo*, ArchiveHeapInfo*, char*, unsigned long) archiveBuilder.cpp:1573
>     #2 0x105245e60 in ArchiveBuilder::write_archive(FileMapInfo*, ArchiveHeapInfo*) archiveBuilder.cpp:1634
>     #3 0x106084fd4 in MetaspaceShared::write_static_archive(ArchiveBuilder*, FileMapInfo*, ArchiveHeapInfo*) metaspaceShared.cpp:1053
>     #4 0x10608411c in MetaspaceShared::preload_and_dump_impl(StaticArchiveBuilder&, JavaThread*) metaspaceShared.cpp:1030
>     #5 0x1060837b8 in MetaspaceShared::preload_and_dump(JavaThread*) metaspaceShared.cpp:812
>     #6 0x10660457c in Threads::create_vm(JavaVMInitArgs*, bool*) threads.cpp:892
>     #7 0x105ca60dc in JNI_CreateJavaVM jni.cpp:3680
>     #8 0x100fbe4d0 in JavaMain java.c:494
>     #9 0x100fc54fc in ThreadJavaMain java_md_macosx.m:679
>     #10 0x197372f90 in _pthread_start+0x84 (libsystem_pthread.dylib:arm64e+0x6f90)
>     #11 0x19736dd30 in thread_start+0x4 (libsystem_pthread.dylib:arm64e+0x1d30)

LGTM.
David's (@dholmes-ora) comment touches a widespread inconsistency. Historically, almost nobody cared about distinguishing between naturally signed and unsigned entities. 

A clean solution would be to declare `unitsize` as `unsigned int` and adapt all callers. I'm not sure if widening the scope of this otherwise trivial change is justified.

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Marked as reviewed by lucy (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26037#pullrequestreview-2971842726