Date: Mon, 26 Jun 2023 08:59:14 -0700 From: Mark Millard <marklmi@yahoo.com> To: John F Carr <jfc@mit.edu> Cc: Current FreeBSD <freebsd-current@freebsd.org>, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: aarch64 main-n263493-4e8d558c9d1c-dirty (so: 2023-Jun-10) Kyuafile run: "Fatal data abort" crash during vnet_register_sysinit Message-ID: <79849041-5E0E-4244-9BA7-F7F1C673F31F@yahoo.com> In-Reply-To: <2E9684B7-9359-4A3D-A0C2-C1D2B221F2C4@mit.edu> References: <3FD359F8-CFCC-400F-B6DE-B635B747DE7F.ref@yahoo.com> <3FD359F8-CFCC-400F-B6DE-B635B747DE7F@yahoo.com> <CB3569D4-8FEE-4DD3-83CE-885789E79E18@mit.edu> <4A380699-7C9E-4E2E-8DCD-F9ECC2112667@yahoo.com> <64F18C76-BD2A-4608-A8CC-38AC2820FC12@yahoo.com> <2E9684B7-9359-4A3D-A0C2-C1D2B221F2C4@mit.edu>
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On Jun 26, 2023, at 07:29, John F Carr <jfc@mit.edu> wrote:
>
>
>> On Jun 26, 2023, at 04:32, Mark Millard <marklmi@yahoo.com> wrote:
>>
>> On Jun 24, 2023, at 17:25, Mark Millard <marklmi@yahoo.com> wrote:
>>
>>> On Jun 24, 2023, at 14:26, John F Carr <jfc@mit.edu> wrote:
>>>
>>>>
>>>>> On Jun 24, 2023, at 13:00, Mark Millard <marklmi@yahoo.com> wrote:
>>>>>
>>>>> The running system build is a non-debug build (but
>>>>> with symbols not stripped).
>>>>>
>>>>> The HoneyComb's console log shows:
>>>>>
>>>>> . . .
>>>>> GEOM_STRIPE: Device stripe.IMfBZr destroyed.
>>>>> GEOM_NOP: Device md0.nop created.
>>>>> g_vfs_done():md0.nop[READ(offset=5885952, length=8192)]error = 5
>>>>> GEOM_NOP: Device md0.nop removed.
>>>>> GEOM_NOP: Device md0.nop created.
>>>>> g_vfs_done():md0.nop[READ(offset=5935104, length=4096)]error = 5
>>>>> g_vfs_done():md0.nop[READ(offset=5935104, length=4096)]error = 5
>>>>> GEOM_NOP: Device md0.nop removed.
>>>>> GEOM_NOP: Device md0.nop created.
>>>>> GEOM_NOP: Device md0.nop removed.
>>>>> Fatal data abort:
>>>>> x0: ffffa02506e64400
>>>>> x1: ffff0001ea401880 (g_raid3_post_sync + 3a145f8)
>>>>> x2: 4b
>>>>> x3: a343932b0b22fb30
>>>>> x4: 0
>>>>> x5: 3310b0d062d0e1d
>>>>> x6: 1d0e2d060d0b3103
>>>>> x7: 0
>>>>> x8: ea325df8
>>>>> x9: ffff0001eec946d0 ($d.6 + 0)
>>>>> x10: ffff0001ea401880 (g_raid3_post_sync + 3a145f8)
>>>>> x11: 0
>>>>> x12: 0
>>>>> x13: ffff000000cd8960 (lock_class_mtx_sleep + 0)
>>>>> x14: 0
>>>>> x15: ffffa02506e64405
>>>>> x16: ffff0001eec94860 (_DYNAMIC + 160)
>>>>> x17: ffff00000063a450 (ifc_attach_cloner + 0)
>>>>> x18: ffff0001eb290400 (g_raid3_post_sync + 48a3178)
>>>>> x19: ffff0001eec94600 (vnet_epair_init_vnet_init + 0)
>>>>> x20: ffff000000fa5b68 (vnet_sysinit_sxlock + 18)
>>>>> x21: ffff000000d8e000 (sdt_vfs_vop_vop_spare4_return + 0)
>>>>> x22: ffff000000d8e000 (sdt_vfs_vop_vop_spare4_return + 0)
>>>>> x23: ffffa0000042e500
>>>>> x24: ffffa0000042e500
>>>>> x25: ffff000000ce0788 (linker_lookup_set_desc + 0)
>>>>> x26: ffffa0203cdef780
>>>>> x27: ffff0001eec94698 (__set_sysinit_set_sym_if_epairmodule_sys_init + 0)
>>>>> x28: ffff000000d8e000 (sdt_vfs_vop_vop_spare4_return + 0)
>>>>> x29: ffff0001eb290430 (g_raid3_post_sync + 48a31a8)
>>>>> sp: ffff0001eb290400
>>>>> lr: ffff0001eec82a4c ($x.1 + 3c)
>>>>> elr: ffff0001eec82a60 ($x.1 + 50)
>>>>> spsr: 60000045
>>>>> far: ffff0002d8fba4c8
>>>>> esr: 96000046
>>>>> panic: vm_fault failed: ffff0001eec82a60 error 1
>>>>> cpuid = 14
>>>>> time = 1687625470
>>>>> KDB: stack backtrace:
>>>>> db_trace_self() at db_trace_self
>>>>> db_trace_self_wrapper() at db_trace_self_wrapper+0x30
>>>>> vpanic() at vpanic+0x13c
>>>>> panic() at panic+0x44
>>>>> data_abort() at data_abort+0x2fc
>>>>> handle_el1h_sync() at handle_el1h_sync+0x14
>>>>> --- exception, esr 0x96000046
>>>>> $x.1() at $x.1+0x50
>>>>> vnet_register_sysinit() at vnet_register_sysinit+0x114
>>>>> linker_load_module() at linker_load_module+0xae4
>>>>> kern_kldload() at kern_kldload+0xfc
>>>>> sys_kldload() at sys_kldload+0x60
>>>>> do_el0_sync() at do_el0_sync+0x608
>>>>> handle_el0_sync() at handle_el0_sync+0x44
>>>>> --- exception, esr 0x56000000
>>>>> KDB: enter: panic
>>>>> [ thread pid 70419 tid 101003 ]
>>>>> Stopped at kdb_enter+0x44: str xzr, [x19, #3200]
>>>>> db>
>>>>
>>>> The failure appears to be initializing module if_epair.
>>>
>>> Yep: trying:
>>>
>>> # kldload if_epair.ko
>>>
>>> was enough to cause the crash. (Just a HoneyComb context at
>>> that point.)
>>>
>>> I tried media dd'd from the recent main snapshot, booting the
>>> same system. No crash. I moved my build boot media to some
>>> other systems and tested them: crashes. I tried my boot media
>>> built optimized for Cortex-A53 or Cortex-X1C/Cortex-A78C
>>> instead of Cortex-A72: no crashes. (But only one system can
>>> use the X1C/A78C code in that build.)
>>>
>>> So variation testing only gets the crashes for my builds
>>> that are code-optimized for Cortex-A72's. The same source
>>> tree vintage built for cortex-53 or Cortex-X1C/Cortex-A78C
>>> optimization does not get the crashes. But I also
>>> demonstrated an optmized for Cortex-A72 build from 2023-Mar
>>> that gets the crash.
>>>
>>> The last time I ran into one of these "crashes tied to
>>> cortex-a72 code optimization" examples it turned out to be
>>> some missing memory-model management code in FreeBSD's USB
>>> code. But being lucky enough to help identify a FreeBSD
>>> source code problem again seems not that likely. It could
>>> easily be a code generation error by clang for all I know.
>>>
>>> So, unless at some point I produce fairly solid evidence
>>> that the code actually running is messed up by FreeBSD
>>> source code, this should likely be treated as "blame the
>>> operator" and should likely be largely ignored as things
>>> are. (Just My Problem, as I want the Cortex-A72 optimized
>>> builds.)
>>
>> Turns out that the source code in question is the
>> assignment to V_epair_cloner below:
>>
>> static void
>> vnet_epair_init(const void *unused __unused)
>> {
>> struct if_clone_addreq req = {
>> .match_f = epair_clone_match,
>> .create_f = epair_clone_create,
>> .destroy_f = epair_clone_destroy,
>> };
>> V_epair_cloner = ifc_attach_cloner(epairname, &req);
>> }
>> VNET_SYSINIT(vnet_epair_init, SI_SUB_PSEUDO, SI_ORDER_ANY,
>> vnet_epair_init, NULL);
>>
>> Example code when not optimizing for the Cortex-A72:
>>
>> 11a4c: d0000089 adrp x9, 0x23000
>> 11a50: f9400248 ldr x8, [x18]
>> 11a54: f942c508 ldr x8, [x8, #1416]
>> 11a58: f943d929 ldr x9, [x9, #1968]
>> 11a5c: a9437bfd ldp x29, x30, [sp, #48]
>> 11a60: f9401508 ldr x8, [x8, #40]
>> 11a64: f8296900 str x0, [x8, x9]
>>
>> The code when optmizing for the Cortex-A72:
>>
>> 11a4c: f9400248 ldr x8, [x18]
>> 11a50: f942c508 ldr x8, [x8, #1416]
>> 11a54: d503201f nop
>> 11a58: 1008e3c9 adr x9, #72824
>> 11a5c: f9401508 ldr x8, [x8, #40]
>> 11a60: f8296900 str x0, [x8, x9]
>> 11a64: a9437bfd ldp x29, x30, [sp, #48]
>>
>> It is the "str x0, [x8, x9]" that vm_fault's for
>> the optimized code.
>>
>> So:
>>
>> 11a4c: d0000089 adrp x9, 0x23000
>> 11a58: f943d929 ldr x9, [x9, #1968]
>>
>> was optimized via replacement by:
>>
>> 11a58: 1008e3c9 adr x9, #72824
>>
>> I.e., the optimization is based on the offset from
>> the instruction being fixed in order to produce the
>> value in x9, even if the instruction is relocated.
>>
>> This resulted in the specific x9 value shown in
>> the x8/x9 pair:
>>
>> x8: ea325df8
>> x9: ffff0001eec946d0
>>
>> which total's to the fault address (value
>> in far):
>>
>> far: ffff0002d8fba4c8
>>
>>
> Is this the same as bug 264094?
>
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=264094
Well, the not Cortex-A72 optimized .o stage code vs. the
Cortex-A72 optimized .o stage code looks like:
(not Cortex-A72 optimized)
3c: 90000009 adrp x9, 0x0 <vnet_epair_init+0x3c>
40: f9400248 ldr x8, [x18]
44: f942c508 ldr x8, [x8, #1416]
48: f9400129 ldr x9, [x9]
4c: a9437bfd ldp x29, x30, [sp, #48]
50: f9401508 ldr x8, [x8, #40]
54: f8296900 str x0, [x8, x9]
vs. (Cortex-A72 optimized)
3c: f9400248 ldr x8, [x18]
40: f942c508 ldr x8, [x8, #1416]
44: 90000009 adrp x9, 0x0 <vnet_epair_init+0x44>
48: f9400129 ldr x9, [x9]
4c: f9401508 ldr x8, [x8, #40]
50: f8296900 str x0, [x8, x9]
54: a9437bfd ldp x29, x30, [sp, #48]
(The x29 lines have a different purpose but I
show the sequencing as shown by objdump to show
that it is basically an ordering difference at
the .o stage.)
As for if_epair.kld production the .meta files show:
CMD ld -m aarch64elf -warn-common --build-id=sha1 -r -o if_epair.kld if_epair.o
CMD ctfmerge -L VERSION -g -o if_epair.kld if_epair.o
CMD :> export_syms
CMD awk -f /usr/main-src/sys/conf/kmod_syms.awk if_epair.kld export_syms | xargs -J% objcopy % if_epair.kld
CWD /usr/obj/BUILDs/main-CA72-nodbg-clang-alt/usr/main-src/arm64.aarch64/sys/GENERIC-NODBG-CA72/modules/usr/main-src/sys/modules/if_epair
vs.
CMD ld -m aarch64elf -warn-common --build-id=sha1 -r -o if_epair.kld if_epair.o
CMD ctfmerge -L VERSION -g -o if_epair.kld if_epair.o
CMD :> export_syms
CMD awk -f /usr/main-src/sys/conf/kmod_syms.awk if_epair.kld export_syms | xargs -J% objcopy % if_epair.kld
CWD /usr/obj/BUILDs/main-CA72-nodbg-clang/usr/main-src/arm64.aarch64/sys/GENERIC-NODBG-CA72/modules/usr/main-src/sys/modules/if_epair
It looks to me like the code ordering differences in the .o's
may be all that lead to the differing .kld results for setting
x9 . If so, it is not good to be that dependent on minor .o
stage code generation differences for if things will be
operational vs. not.
===
Mark Millard
marklmi at yahoo.com
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