head -r346588 accidentally added use of cmpb that is not supported on old PPC970's, such as on old PowerMac G5s. This turns out to provide a good test case for the handling of such invalid instruction encodings and it exposed a locking problem reported by the debug kernel. I used https://artifact.ci.freebsd.org/snapshot/head/r346589/powerpc/powerpc64/ and some later ones in testing something else and ran into the issue below. (-r346588 was not present for powerpc64.) The below is from a later one: panic: mtx_lock of spin mutex WWV @ /mnt/usr/src/sys/powerpc/aim/mmu_oea64.c:2812 For reference, line 2812 is: PMAP_LOCK(pm); panic is reached via the following call chain, shown as part of a backtrace (typed from screen pictures): .__mtx_lock_flags+0xd4 .moea64_sync_icache+0x48 .pmap_sync_icache+0x90 .ppc_instr_emulate+0x1b4 .trap+0x10fc .powerpc_interrupt+0x2cc user PGM trap by 0x810053bb4: srr1=0x900000000008d032 r1=0x3ffffffffffffcc00 cr=0x20002024 xer=0 ctr=0x1 r2=0x81007bdd0 frame=0xe000000070ca9810 It was thread pid 28 tid 100097 Actually r346589 was at line :2811 and had the following differences: .ppc_intr_emulate+0x19c .trap+0x1004 frame=0xe000000070ca9848 I will note that -r346670 has notes on the lists for running into: mtx_lock of spin mutex(null) in .../kern/subr_bus.c:620 and being isolated by a bisect for being the first exposure in that context. This was not a powerpc64 context and may be completely unrelated. But folks seemed confused about how -r346670 might lead to such a panic.
(In reply to Mark Millard from comment #0) head -r347492 changed what made head -r346588 a good test case for the mtx_lock issue: it removed use of the illegal instructions (as far as pre-power6 processors are concerned). So, either using the range that is a test-case on such older power/powerpc64 or other means of inducing a test case is now needed.