Unexpected segmentation fault outside heap in gctest on Linux/x86 both in soft- and mprotect-vdb modes

[ivmai]

Source: master (7f1503d)
Build: https://app.travis-ci.com/github/ivmai/bdwgc/jobs/624768375
Host: Ubuntu 22.04/x86_64 (but code is compiled to 32-bit x86)
Compiler: clang 18.1.8
Config: CFLAGS_EXTRA="-m32 -funsigned-char -D _FORTIFY_SOURCE=2 -D GC_GCJ_MARK_DESCR_OFFSET=32 -D NO_LONGLONG64" CONF_OPTIONS="--enable-gc-assertions" GCTEST_WITH_MPROTECT_VDB=true

Output (gctest.log, soft-vdb mode):

Supported VDBs: manual soft mprotect
Switched to incremental mode
Reading dirty bits from /proc
FAIL gctest (exit status: 139)

Output (gctest, mprotect-vdb mode):

Supported VDBs: manual soft mprotect
Switched to incremental mode
Emulating dirty bits with mprotect/signals
Unexpected segmentation fault outside heap at 0x813dec

[ivmai]

Seems to be related to #652