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Date: Sun, 6 May 2018 09:42:09 +0200
From: Sedat Dilek <sedat.dilek@...il.com>
To: Matthias Kaehlcke <mka@...omium.org>
Cc: lkml <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
Nick Desaulniers <nick.desaulniers@...il.com>,
Manoj Gupta <manojgupta@...omium.org>
Subject: Re: Clang patch stacks for LTS kernels (v4.4 and v4.9) and status update
On Wed, Apr 25, 2018 at 1:06 AM, Matthias Kaehlcke <mka@...omium.org> wrote:
> On Tue, Apr 24, 2018 at 01:54:29PM +0200, Sedat Dilek wrote:
>> Hi Matthias,
>>
>> a big thank you for giving all the informations!
>>
>> I used your mka/llvm/v4.14_ext Git tree...
>>
>> https://chromium.googlesource.com/chromiumos/third_party/kernel/+log/sandbox/mka/llvm/v4.14_ext
>>
>> ...and was able to compile with clang-6.0 from Debian/buster64 with...
>>
>> ...reverting the clang-3/clang-4 patches...
>>
>> user$ for p in 69e44656ae43 222b88977a00 cdfcf1e45537 26f14c9225a6
>> 0385a18e9995 68dab143c9b4 ; do echo [ $p ] ; LC_ALL=C git revert
>> --no-edit $p ; done
>>
>> 0001-Revert-CLANG3-core-clang-work-around-x86-regparm-int.patch
>> 0002-Revert-CLANG4-futex-don-t-optimize-futex_detect_cmpx.patch
>> 0003-Revert-CLANG4-Disable-lkdtm-when-ftrace-is-enabled.patch
>> 0004-Revert-CLANG4-arm64-prefetch-Use-__builtin_arm_prefe.patch
>> 0005-Revert-CLANG4-kbuild-Add-meabi-gnu-to-the-clang-para.patch
>> 0006-Revert-CLANG4-crypto-arm64-aes-ce-Explicitly-pass-th.patch
>>
>> ...and needed two additional patches from upstream:
>>
>> 0007-kbuild-clang-remove-crufty-HOSTCFLAGS.patch <--- Label with
>> BACKPORT (XXX: Backported; Required when using HOSTCC in make-line,
>> see below)
>> 0008-x86-xen-remove-the-use-of-VLAIS.patch <--- Label with UPSTREAM
>> (XXX: cherry-picked)
>>
>> These 3 patches in your Git branch are in Linux v4.14.36...
>>
>> 9af5ddf981ed BACKPORT: kbuild: disable clang's default use of
>> -fmerge-all-constants
>> f24088a3842c BACKPORT: kbuild: Set KBUILD_CFLAGS before incl. arch Makefile
>> d4dfe384346d UPSTREAM: kbuild: fix linker feature test macros when
>> cross compiling with Clang
>>
>> ...and can be dropped.
>> I do not know your work-flow/policy: Maybe you want to keep your
>> patch-stack against vanilla Linux v4.14 - without stables from
>> linux-stable-4.14.y.
>
> Yes, these patch stacks are based on vanilla Linux v4.14, one reason
> is that it isn't a moving target. Also I think it makes it easier for
> folks not merging LTS (though they probably should!) to locate all
> patches, and it's fairly trivial to skip the (currently) few patches
> not needed with the -stable tree.
>
>> For easy switching "mycompiler" I use a wrapper-script:
>>
>> root# cat /usr/bin/mycompiler
>> #!/bin/bash
>>
>> clang-6.0 "$@"
>> - EOF -
>>
>> user$ cp -v /boot/config-4.14.35-1-iniza-amd64 .config
>> user$ MAKE="make V=1" ; COMPILER="mycompiler" ;
>> MAKE_OPTS="CC=$COMPILER HOSTCC=$COMPILER"
>> user$ yes "" | $MAKE $MAKE_OPTS oldconfig && $MAKE $MAKE_OPTS
>> silentoldconfig < /dev/null
>>
>> The diffconfig to my current kernel-config-4.14 looks like this...
>>
>> user$ ./scripts/diffconfig /boot/config-4.14.35-1-iniza-amd64 .config
>> -ARCH_HAS_REFCOUNT y
>> -BPF_JIT_ALWAYS_ON n
>> -EXOFS_DEBUG n
>> -EXOFS_FS m
>> -GENERIC_CPU_VULNERABILITIES y
>> -KASAN n
>> -ORE m
>> -PAGE_TABLE_ISOLATION y
>> -RETPOLINE y
>> -UNWINDER_FRAME_POINTER n
>> -UNWINDER_GUESS n
>> -UNWINDER_ORC y
>> +FRAME_POINTER y
>> +FRAME_POINTER_UNWINDER y
>> +GUESS_UNWINDER n
>> +HAVE_ARCH_KMEMCHECK y
>> +HAVE_RELIABLE_STACKTRACE y
>> +ORC_UNWINDER n
>>
>> Unfortunately, I cannot boot into the generated kernel on bare metal.
>>
>> Checking with QEMU (version: 2.12~rc3) and catching earlyprintk, I see this...
>>
>> user$ echo $KPATH
>> $HOME/src/linux-kernel/important-files
>>
>> user$ ls -al
>> insgesamt 344916
>> drwxr-xr-x 2 sdi sdi 4096 Apr 24 13:15 .
>> drwxr-xr-x 20 sdi sdi 4096 Apr 24 13:13 ..
>> -rw-r--r-- 1 sdi sdi 4528416 Apr 24 12:42 bzImage
>> lrwxrwxrwx 1 sdi sdi 35 Apr 24 13:15 initrd.img ->
>> initrd.img-4.14.0-1-iniza-llvmlinux
>> -rw-r--r-- 1 sdi sdi 25572955 Apr 24 13:08
>> initrd.img-4.14.0-1-iniza-llvmlinux
>> -rw-r--r-- 1 sdi sdi 2887195 Apr 24 12:42 System.map
>> -rwxr-xr-x 1 sdi sdi 326116744 Apr 24 12:42 vmlinux
>>
>> user$ sudo qemu-system-x86_64 -enable-kvm -M pc -kernel $KPATH/bzImage
>> -initrd $KPATH/initrd.img -m 512 -net none -serial stdio -append
>> "root=/dev/ram0 console=ttyS0 hung_task_panic=1
>> earlyprintk=ttyS0,115200"
>>
>> Probing EDD (edd=off to disable)... ok
>> [ 0.000000] Linux version 4.14.0-1-iniza-llvmlinux
>> (sedat.dilek@...il.com@...za) (clang version 6.0.0-1
>> (tags/RELEASE_600/final)) #1 SMP Tue Apr 24 12:42:21 CEST 2018
>> [ 0.000000] Command line: root=/dev/ram0 console=ttyS0
>> hung_task_panic=1 earlyprintk=ttyS0,115200
>> [ 0.000000] x86/fpu: x87 FPU will use FXSAVE
>> [ 0.000000] e820: BIOS-provided physical RAM map:
>> [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
>> [ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
>> [ 0.000000] BIOS-e820: [mem 0x00000000000f0000-0x00000000000fffff] reserved
>> [ 0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000001ffdffff] usable
>> [ 0.000000] BIOS-e820: [mem 0x000000001ffe0000-0x000000001fffffff] reserved
>> [ 0.000000] BIOS-e820: [mem 0x00000000feffc000-0x00000000feffffff] reserved
>> [ 0.000000] BIOS-e820: [mem 0x00000000fffc0000-0x00000000ffffffff] reserved
>> [ 0.000000] bootconsole [earlyser0] enabled
>> [ 0.000000] NX (Execute Disable) protection: active
>> [ 0.000000] random: fast init done
>> [ 0.000000] SMBIOS 2.8 present.
>> [ 0.000000] DMI: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> 1.11.1-1 04/01/2014
>> [ 0.000000] Hypervisor detected: KVM
>> [ 0.000000] tsc: Fast TSC calibration using PIT
>> [ 0.000000] e820: last_pfn = 0x1ffe0 max_arch_pfn = 0x400000000
>> [ 0.000000] x86/PAT: PAT not supported by CPU.
>> [ 0.000000] x86/PAT: Configuration [0-7]: WB WT UC- UC WB WT UC- UC
>> Memory KASLR using RDTSC...
>> [ 0.000000] found SMP MP-table at [mem 0x000f5d60-0x000f5d6f]
>> mapped at [ffffffffff000d60]
>> [ 0.000000] RAMDISK: [mem 0x1e77c000-0x1ffdffff]
>> [ 0.000000] ACPI: Early table checksum verification disabled
>> [ 0.000000] ACPI: RSDP 0x00000000000F5B90 000014 (v00 BOCHS )
>> [ 0.000000] ACPI: RSDT 0x000000001FFE157C 000030 (v01 BOCHS
>> BXPCRSDT 00000001 BXPC 00000001)
>> [ 0.000000] ACPI: FACP 0x000000001FFE1458 000074 (v01 BOCHS
>> BXPCFACP 00000001 BXPC 00000001)
>> [ 0.000000] ACPI: DSDT 0x000000001FFE0040 001418 (v01 BOCHS
>> BXPCDSDT 00000001 BXPC 00000001)
>> [ 0.000000] ACPI: FACS 0x000000001FFE0000 000040
>> [ 0.000000] ACPI: APIC 0x000000001FFE14CC 000078 (v01 BOCHS
>> BXPCAPIC 00000001 BXPC 00000001)
>> [ 0.000000] ACPI: HPET 0x000000001FFE1544 000038 (v01 BOCHS
>> BXPCHPET 00000001 BXPC 00000001)
>> [ 0.000000] No NUMA configuration found
>> [ 0.000000] Faking a node at [mem 0x0000000000000000-0x000000001ffdffff]
>> [ 0.000000] NODE_DATA(0) allocated [mem 0x1e777000-0x1e77bfff]
>> [ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
>> [ 0.000000] kvm-clock: cpu 0, msr 0:1e76f001, primary cpu clock
>> [ 0.000000] kvm-clock: using sched offset of 528742140 cycles
>> [ 0.000000] clocksource: kvm-clock: mask: 0xffffffffffffffff
>> max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
>> [ 0.000000] Zone ranges:
>> [ 0.000000] DMA [mem 0x0000000000001000-0x0000000000ffffff]
>> [ 0.000000] DMA32 [mem 0x0000000001000000-0x000000001ffdffff]
>> [ 0.000000] Normal empty
>> [ 0.000000] Device empty
>> [ 0.000000] Movable zone start for each node
>> [ 0.000000] Early memory node ranges
>> [ 0.000000] node 0: [mem 0x0000000000001000-0x000000000009efff]
>> [ 0.000000] node 0: [mem 0x0000000000100000-0x000000001ffdffff]
>> [ 0.000000] Initmem setup node 0 [mem 0x0000000000001000-0x000000001ffdffff]
>> [ 0.000000] ACPI: PM-Timer IO Port: 0x608
>> [ 0.000000] ACPI: LAPIC_NMI (acpi_id[0xff] dfl dfl lint[0x1])
>> [ 0.000000] IOAPIC[0]: apic_id 0, version 17, address 0xfec00000, GSI 0-23
>> [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 0 global_irq 2 dfl dfl)
>> [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 5 global_irq 5 high level)
>> [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 9 global_irq 9 high level)
>> [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 10 global_irq 10 high level)
>> [ 0.000000] ACPI: INT_SRC_OVR (bus 0 bus_irq 11 global_irq 11 high level)
>> [ 0.000000] Using ACPI (MADT) for SMP configuration information
>> [ 0.000000] ACPI: HPET id: 0x8086a201 base: 0xfed00000
>> [ 0.000000] smpboot: Allowing 1 CPUs, 0 hotplug CPUs
>> [ 0.000000] PM: Registered nosave memory: [mem 0x00000000-0x00000fff]
>> [ 0.000000] PM: Registered nosave memory: [mem 0x0009f000-0x0009ffff]
>> [ 0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000effff]
>> [ 0.000000] PM: Registered nosave memory: [mem 0x000f0000-0x000fffff]
>> [ 0.000000] e820: [mem 0x20000000-0xfeffbfff] available for PCI devices
>> [ 0.000000] Booting paravirtualized kernel on KVM
>> [ 0.000000] clocksource: refined-jiffies: mask: 0xffffffff
>> max_cycles: 0xffffffff, max_idle_ns: 7645519600211568 ns
>> [ 0.000000] setup_percpu: NR_CPUS:512 nr_cpumask_bits:512
>> nr_cpu_ids:1 nr_node_ids:1
>> [ 0.000000] percpu: Embedded 37 pages/cpu @ffff96dd9e400000 s114392
>> r8192 d28968 u2097152
>> [ 0.000000] KVM setup async PF for cpu 0
>> [ 0.000000] kvm-stealtime: cpu 0, msr 1e40d900
>> [ 0.000000] Built 1 zonelists, mobility grouping on. Total pages: 128872
>> [ 0.000000] Policy zone: DMA32
>> [ 0.000000] Kernel command line: root=/dev/ram0 console=ttyS0
>> hung_task_panic=1 earlyprintk=ttyS0,115200
>> [ 0.000000] PID hash table entries: 2048 (order: 2, 16384 bytes)
>> [ 0.000000] Memory: 474480K/523768K available (7639K kernel code,
>> 1005K rwdata, 2936K rodata, 1636K init, 688K bss, 49288K reserved, 0K
>> cma-reserved)
>> [ 0.000000] ftrace: allocating 27586 entries in 108 pages
>> [ 0.004000] Hierarchical RCU implementation.
>> [ 0.004000] RCU restricting CPUs from NR_CPUS=512 to nr_cpu_ids=1.
>> [ 0.004000] RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=1
>> [ 0.004000] NR_IRQS: 33024, nr_irqs: 256, preallocated irqs: 16
>> [ 0.004000] Console: colour VGA+ 80x25
>> [ 0.004000] console [ttyS0] enabled
>> [ 0.004000] console [ttyS0] enabled
>> [ 0.004000] bootconsole [earlyser0] disabled
>> [ 0.004000] bootconsole [earlyser0] disabled
>> [ 0.004000] clocksource: hpet: mask: 0xffffffff max_cycles:
>> 0xffffffff, max_idle_ns: 19112604467 ns
>> [ 0.004000] general protection fault: 0000 [#1] SMP
>> [ 0.004000] Modules linked in:
>> [ 0.004000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted
>> 4.14.0-1-iniza-llvmlinux #1
>> [ 0.004000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
>> BIOS 1.11.1-1 04/01/2014
>> [ 0.004000] task: ffffffffaa610480 task.stack: ffffffffaa600000
>> [ 0.004000] RIP: 0010:irq_work_tick+0x9d/0x110
>> [ 0.004000] RSP: 0000:ffff96dd9e403e58 EFLAGS: 00010046
>> [ 0.004000] RAX: 0000000000000082 RBX: ffff96dd9e411d80 RCX: adecc9cc04e2ca00
>> [ 0.004000] RDX: 000000000001ba00 RSI: fffffffffffffed4 RDI: ffff96dd9e41ba38
>> [ 0.004000] RBP: ffff96dd9e403e78 R08: 0000000000000000 R09: 0000000000000018
>> [ 0.004000] R10: 0000000000000000 R11: 0000000000000018 R12: ffffffffaa61bd40
>> [ 0.004000] R13: 0000000000000000 R14: ffffffffaa610480 R15: 0000000000000000
>> [ 0.004000] FS: 0000000000000000(0000) GS:ffff96dd9e400000(0000)
>> knlGS:0000000000000000
>> [ 0.004000] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [ 0.004000] CR2: 00000000ffffffff CR3: 0000000008a09000 CR4: 00000000000006b0
>> [ 0.004000] Call Trace:
>> [ 0.004000] <IRQ>
>> [ 0.004000] update_process_times+0x6e/0xa0
>> [ 0.004000] tick_periodic+0x78/0x90
>> [ 0.004000] tick_handle_periodic+0x26/0x80
>> [ 0.004000] timer_interrupt+0x13/0x20
>> [ 0.004000] __handle_irq_event_percpu+0x106/0x230
>> [ 0.004000] handle_irq_event+0x5a/0xc0
>> [ 0.004000] handle_level_irq+0x11a/0x190
>> [ 0.004000] handle_irq+0x1f/0x30
>> [ 0.004000] do_IRQ+0x4b/0xd0
>> [ 0.004000] common_interrupt+0x93/0x93
>> [ 0.004000] </IRQ>
>> [ 0.004000] RIP: 0010:native_restore_fl+0x12/0x20
>> [ 0.004000] RSP: 0000:ffffffffaa603e10 EFLAGS: 00000286 ORIG_RAX:
>> ffffffffffffffcf
>> [ 0.004000] RAX: 0000000000000001 RBX: ffff96dd9d0c0608 RCX: 0000000000000000
>> [ 0.004000] RDX: ffff96dd9d0c0400 RSI: 0000000000000286 RDI: 0000000000000286
>> [ 0.004000] RBP: ffffffffaa603e18 R08: 0000000000000001 R09: 000000000000003f
>> [ 0.004000] R10: 0000000000000286 R11: 0000000000000007 R12: ffff96dd9d0c0514
>> [ 0.004000] R13: ffff96dd9d0c04e0 R14: ffffffffaa61bd40 R15: ffff96dd9d0c0400
>> [ 0.004000] _raw_spin_unlock_irqrestore+0x1a/0x20
>> [ 0.004000] __setup_irq+0x5d9/0x780
>> [ 0.004000] setup_irq+0x5c/0x90
>> [ 0.004000] hpet_time_init+0x32/0x40
>> [ 0.004000] x86_late_time_init+0x10/0x20
>> [ 0.004000] start_kernel+0x45d/0x580
>> [ 0.004000] x86_64_start_kernel+0x30f/0x320
>> [ 0.004000] secondary_startup_64+0xa5/0xa5
>> [ 0.004000] Code: f0 f0 4c 0f b1 7b f8 4c 89 e3 4d 85 e4 75 cf 48
>> c7 c1 88 5b 01 00 65 48 03 0c 25 d8 a1 00 00 ff 14 25 10 08 62 aa f6
>> c4 02 75 4d <48> 83 39 00 74 3e 31 db 48 87 19 48 85 db 74 34 0f 1f 00
>> 48 8d
>> [ 0.004000] RIP: irq_work_tick+0x9d/0x110 RSP: ffff96dd9e403e58
>> [ 0.004000] ---[ end trace 8c7851007fbc6b6f ]---
>> [ 0.004000] Kernel panic - not syncing: Fatal exception in interrupt
>> [ 0.004000] ---[ end Kernel panic - not syncing: Fatal exception in interrupt
>>
>> Is this saying someting to you?
>
> It doesn't ring a bell, but I can repro it (with different offsets):
>
> [ 0.004000] general protection fault: 0000 [#1] SMP
> [ 0.004000] Modules linked in:
> [ 0.004000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0+ #10
> [ 0.004000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [ 0.004000] task: ffffffffbb410480 task.stack: ffffffffbb400000
> [ 0.004000] RIP: 0010:irq_work_tick+0xaf/0x120
> [ 0.004000] RSP: 0000:ffff96fb5fc03e58 EFLAGS: 00010046
> [ 0.004000] RAX: 0000000000000082 RBX: ffff96fb5fc11d80 RCX: 47e992c1bc778d00
> [ 0.004000] RDX: 000000000001ba00 RSI: fffffffffffffed4 RDI: ffff96fb5fc1ba38
> [ 0.004000] RBP: ffff96fb5fc03e78 R08: 0000000000000000 R09: 0000000000000018
> [ 0.004000] R10: 0000000000000000 R11: 0000000000000018 R12: ffffffffbb41bd40
> [ 0.004000] R13: 0000000000000000 R14: ffffffffbb410480 R15: 0000000000000000
> [ 0.004000] FS: 0000000000000000(0000) GS:ffff96fb5fc00000(0000) knlGS:0000000000000000
> [ 0.004000] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 0.004000] CR2: 00000000ffffffff CR3: 000000001ec09000 CR4: 00000000000006b0
> [ 0.004000] Call Trace:
> [ 0.004000] <IRQ>
> [ 0.004000] update_process_times+0x6e/0xa0
> [ 0.004000] tick_periodic+0x78/0x90
> [ 0.004000] tick_handle_periodic+0x26/0x80
> [ 0.004000] timer_interrupt+0x13/0x20
> [ 0.004000] __handle_irq_event_percpu+0x106/0x230
> [ 0.004000] handle_irq_event+0x5a/0xc0
> [ 0.004000] handle_level_irq+0x11a/0x190
> [ 0.004000] handle_irq+0x1f/0x30
> [ 0.004000] do_IRQ+0x4b/0xd0
> [ 0.004000] common_interrupt+0x93/0x93
> [ 0.004000] </IRQ>
> [ 0.004000] RIP: 0010:native_restore_fl+0xd/0x20
> [ 0.004000] RSP: 0000:ffffffffbb403e08 EFLAGS: 00000282 ORIG_RAX: ffffffffffffffcf
> [ 0.004000] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000
> [ 0.004000] RDX: ffff96fb5f01b800 RSI: 0000000000000282 RDI: 0000000000000282
> [ 0.004000] RBP: ffffffffbb403e10 R08: 0000000000000001 R09: 000000000000003f
> [ 0.004000] R10: ffff96fb5f01b800 R11: 0000000000000007 R12: ffff96fb5f01ba08
> [ 0.004000] R13: ffff96fb5f01b8e0 R14: ffffffffbb41bd40 R15: ffff96fb5f01b800
> [ 0.004000] _raw_spin_unlock_irqrestore+0x1a/0x20
> [ 0.004000] __setup_irq+0x610/0x7b0
> [ 0.004000] setup_irq+0x5b/0x90
> [ 0.004000] hpet_time_init+0x32/0x40
> [ 0.004000] x86_late_time_init+0x10/0x20
> [ 0.004000] start_kernel+0x460/0x580
> [ 0.004000] x86_64_start_kernel+0x30f/0x320
> [ 0.004000] secondary_startup_64+0xa5/0xa5
> [ 0.004000] Code: 4c 0f b1 7b f8 4c 89 e3 4d 85 e4 75 cf 48 c7 c1 88 5b 01 00 65 48 03 0c 25 d8 a1 00 00 ff 14 25 10 08 42 bb a9 00 02 00 00 75 4b <48> 83 39 00 74 3c 31 db 48 87 19 48 85 db 74 32 90 48 8d 7b f8
> [ 0.004000] RIP: irq_work_tick+0xaf/0x120 RSP: ffff96fb5fc03e58
> [ 0.004000] ---[ end trace 08945838e05bf5b2 ]---
> [ 0.004000] Kernel panic - not syncing: Fatal exception in interrupt
> [ 0.004000] ---[ end Kernel panic - not syncing: Fatal exception in interrupt
>
> The exception occurs at 'irq_work_tick+0xaf'
>
> objdump -d -S --start-address=0x$(grep irq_work_tick System.map | sed -e
> "s/ \+.*//") vmlinux | less
>
> ...
> void irq_work_tick(void)
> {
> ffffffff81193200: 55 push %rbp
> ...
> static inline struct llist_node *llist_del_all(struct llist_head *head)
> {
> return xchg(&head->first, NULL);
> ffffffff8119324a: 48 87 19 xchg %rbx,(%rcx)
> while (llnode != NULL) {
> ffffffff8119324d: 48 85 db test %rbx,%rbx
> ffffffff81193250: 74 3f je ffffffff81193291 <irq_work_tick+0x91>
> ffffffff81193252: 0f 1f 40 00 nopl 0x0(%rax)
> ffffffff81193256: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
> ffffffff8119325d: 00 00 00
> work = llist_entry(llnode, struct irq_work, llnode);
> ffffffff81193260: 48 8d 7b f8 lea -0x8(%rbx),%rdi
> flags = work->flags & ~IRQ_WORK_PENDING;
> ffffffff81193264: 4c 8b 7b f8 mov -0x8(%rbx),%r15
> return node->next;
> ffffffff81193268: 4c 8b 23 mov (%rbx),%r12
> ffffffff8119326b: 4d 89 fe mov %r15,%r14
> ffffffff8119326e: 49 83 e6 fe and $0xfffffffffffffffe,%r14
> xchg(&work->flags, flags);
> ffffffff81193272: 4c 89 f0 mov %r14,%rax
> ffffffff81193275: 48 87 43 f8 xchg %rax,-0x8(%rbx)
> work->func(work);
> ffffffff81193279: ff 53 08 callq *0x8(%rbx)
> (void)cmpxchg(&work->flags, flags, flags & ~IRQ_WORK_BUSY);
> ffffffff8119327c: 49 83 e7 fc and $0xfffffffffffffffc,%r15
> ffffffff81193280: 4c 89 f0 mov %r14,%rax
> ffffffff81193283: f0 4c 0f b1 7b f8 lock cmpxchg %r15,-0x8(%rbx)
> ffffffff81193289: 4c 89 e3 mov %r12,%rbx
> while (llnode != NULL) {
> ffffffff8119328c: 4d 85 e4 test %r12,%r12
> ffffffff8119328f: 75 cf jne ffffffff81193260 <irq_work_tick+0x60>
> irq_work_run_list(raised);
> irq_work_run_list(this_cpu_ptr(&lazy_list));
> ffffffff81193291: 48 c7 c1 88 5b 01 00 mov $0x15b88,%rcx
> ffffffff81193298: 65 48 03 0c 25 d8 a1 add %gs:0xa1d8,%rcx
> ffffffff8119329f: 00 00
> ffffffff811932a1: ff 14 25 10 08 c2 81 callq *0xffffffff81c20810
> BUG_ON(!irqs_disabled());
> ffffffff811932a8: a9 00 02 00 00 test $0x200,%eax
> ffffffff811932ad: 75 4b jne ffffffff811932fa <irq_work_tick+0xfa>
> return ACCESS_ONCE(head->first) == NULL;
> ffffffff811932af: 48 83 39 00 cmpq $0x0,(%rcx)
>
>
> I'm no x86/assembly expert, anyway my interpretation is:
>
> 'irq_work_tick+0xaf' corresponds to address 0xffffffff811932af, so the
> exception occurs during the execution of 'cmpq $0x0,(%rcx)' or
> 'ACCESS_ONCE(head->first) == NULL'. The instruction checks if the
> memory location in RCX contains 0. Supposedly the register should
> contain the address of 'head->first', however the value is
> 0x47e992c1bc778d00, which doesn't look like a valid address.
>
> RCX is set shortly before:
>
> ffffffff81193291: 48 c7 c1 88 5b 01 00 mov $0x15b88,%rcx
> ffffffff81193298: 65 48 03 0c 25 d8 a1 add %gs:0xa1d8,%rcx
>
> As stated in https://www.kernel.org/doc/Documentation/this_cpu_ops.txt
> the GS segment register is used by the kernel for per-cpu
> variables. And effectively System.map tells us the offset 0x15b88
> corresponds to the per-cpu variable lazy_list:
>
> 0000000000015b88 d lazy_list
>
> The register dump shows GS with a value of 0xffff96fb5fc00000, which
> looks reasonable.
>
> But wait, right after setting RCX we do this:
>
> ffffffff811932a1: ff 14 25 10 08 c2 81 callq *0xffffffff81c20810
> BUG_ON(!irqs_disabled());
>
> According to my (limited) understanding of x86 calling conventions RCX
> is a caller-saved register, thus the caller should save it on the
> stack to preserve its value across a function call.
> (https://en.wikipedia.org/wiki/X86_calling_conventions)
>
> The call to '*0xffffffff81c20810' appears to be related with
> KVM/paravirtualization:
>
> grep ffffffff81c20810 System.map
> ffffffff81c20810 D pv_irq_ops
>
> Since there is no offset it must be calling the first function in the
> structure, which is 'safe_fl' and points to 'native_save_fl'
> (https://elixir.bootlin.com/linux/v4.14.36/source/arch/x86/kernel/paravirt.c#L316)
>
> objdump -d -S --start-address=0x$(grep native_save_fl System.map | sed
> -e "s/ \+.*//") vmlinux | less
>
> static inline unsigned long native_save_fl(void)
> {
> ffffffff81060240: 55 push %rbp
> ffffffff81060241: 48 89 e5 mov %rsp,%rbp
> ffffffff81060244: 48 83 ec 10 sub $0x10,%rsp
> ffffffff81060248: 65 48 8b 04 25 28 00 mov %gs:0x28,%rax
> ffffffff8106024f: 00 00
> ffffffff81060251: 48 89 45 f8 mov %rax,-0x8(%rbp)
> /*
> * "=rm" is safe here, because "pop" adjusts the stack before
> * it evaluates its effective address -- this is part of the
> * documented behavior of the "pop" instruction.
> */
> asm volatile("# __raw_save_flags\n\t"
> ffffffff81060255: 9c pushfq
> ffffffff81060256: 8f 45 f0 popq -0x10(%rbp)
> "pushf ; pop %0"
> : "=rm" (flags)
> : /* no input */
> : "memory");
>
> return flags;
> ffffffff81060259: 48 8b 45 f0 mov -0x10(%rbp),%rax
> ffffffff8106025d: 65 48 8b 0c 25 28 00 mov %gs:0x28,%rcx
> ffffffff81060264: 00 00
> ffffffff81060266: 48 3b 4d f8 cmp -0x8(%rbp),%rcx
> ffffffff8106026a: 75 06 jne ffffffff81060272 <native_save_fl+0x32>
> ffffffff8106026c: 48 83 c4 10 add $0x10,%rsp
> ffffffff81060270: 5d pop %rbp
> ffffffff81060271: c3 retq
> ffffffff81060272: e8 09 ec 01 00 callq ffffffff8107ee80 <__stack_chk_fail>
> ffffffff81060277: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
> ffffffff8106027e: 00 0
>
> At 0xffffffff8106025d this clobbers RCX! I don't know why clang
> doesn't save the value on the stack before calling native_save_fl(),
> but that seems to be the problem.
>
> Again, I'm not an expert in this area and ventured into territory
> unknown to me, so please excuse if I got something totally wrong ...
>
Hi Matthias,
again you helped me a lot.
I recalled that I had success in the early days of llvmlinux with...
CONFIG_PARAVIRT=n
...as suggested by Steve Rostedt.
This needed some more hackish kconfig kungfu these days - patches attached.
In the end I could boot into a 4.14.37-1-iniza-llvmlinux kernel
(kernel-config and dmesg-log attached).
Concerning your analysis...
Is this a clang-bug?
Or can this be solved in the linux-kernel code?
What are your suggestion?
And can you help on getting this fixed with the help of your Chromium
team and/or bring it to the right persons?
IMHO an analysis like you did might help, too.
I am not an expert in this area to say it is good/correct but I could
follow and read it like a thriller.
Where is Lieutenant Columbo when you need him :-)?
Moreover, a test-case can be helpful, e.g. "Is clang clobbering RCX?"
when it's a clang-bug.
I tried to find some suitable test-case myself.
The clang-source has a test-dir, but this is new to me.
I tried to run a single test like test/Sema/asm.c in [1] with
llvm-tools Debian-package which ships "lit.py" script.
Not sure if this is a suitable for x86-64 (amd64) as the first line says...
// RUN: %clang_cc1 %s -Wno-private-extern -triple i386-pc-linux-gnu
-verify -fsyntax-only
root# cd /path/to/clang-source
root# python /usr/lib/llvm-7/build/utils/lit/lit.py -sv test/Sema
lit.py: /usr/lib/llvm-7/build/utils/lit/lit/TestingConfig.py:101:
fatal: unable to parse config file
'/path/to/clang-source/test/lit.cfg.py', traceback: Traceback (most
recent call last):
File "/usr/lib/llvm-7/build/utils/lit/lit/TestingConfig.py", line
88, in load_from_path
exec(compile(data, path, 'exec'), cfg_globals, None)
File "/home/sdi/src/linux-kernel/clang/test/lit.cfg.py", line 25, in <module>
config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
AttributeError: 'NoneType' object has no attribute 'use_lit_shell'
Not sure if you have any experiences in this area, but I think asking
on llvm-dev is a good idea.
If we have a reproducible test-case we could ask on llvm-dev?
In the case of linux-kernel...
Ask Linux/x86 folks for a test-case to see if the compiler clobbers RCX?
Show your analysis to Linux/(x86)/KVM folks?
Some ideas.
Regards,
- Sedat -
[1] https://raw.githubusercontent.com/llvm-mirror/clang/master/test/Sema/asm.c
[2] https://llvm.org/docs/CommandGuide/lit.html
[3] https://llvm.org/docs/TestingGuide.html
[4] https://llvm.org/docs/TestSuiteMakefileGuide.html
> For the record: a Chrome OS v4.14.35 kernel ('based' on the
> sandbox/mka stack) built with clang still boots on an actual x86
> device.
>
I believe you, really.
Can you give me your kernel-config?
What is the setting of CONFIG_PARAVIRT?
Thank you.
Regards,
- Sedat -
View attachment "dmesg_4.14.37-1-iniza-llvmlinux.txt" of type "text/plain" (66187 bytes)
View attachment "0001-x86-llvmlinux-Mark-CONFIG_PARAVIRT-as-BROKEN.patch" of type "text/x-patch" (701 bytes)
View attachment "0002-x86-llvmlinux-Fix-kconfig-dependencies-when-CONFIG_P.patch" of type "text/x-patch" (1208 bytes)
Download attachment "config-4.14.37-1-iniza-llvmlinux" of type "application/octet-stream" (195387 bytes)
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