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    Subject[PATCH] x86/hweight: Don't clobber %rdi
    Date
    From: Ville Syrjälä <ville.syrjala@linux.intel.com>

    The caller expects %rdi to remain intact, push+pop it make that happen.

    Fixes the following kind of explosions on my core2duo machine when
    trying to reboot or shut down:

    general protection fault: 0000 [#1] PREEMPT SMP
    Modules linked in: i915 i2c_algo_bit drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea drm netconsole configfs binfmt_misc iTCO_wdt psmouse pcspkr snd_hda_codec_idt e100 coretemp hwmon snd_hda_codec_generic i2c_i801 mii i2c_smbus lpc_ich mfd_core snd_hda_intel uhci_hcd snd_hda_codec snd_hwdep snd_hda_core ehci_pci 8250 ehci_hcd snd_pcm 8250_base usbcore evdev serial_core usb_common parport_pc parport snd_timer snd soundcore
    CPU: 0 PID: 3070 Comm: reboot Not tainted 4.8.0-rc1-perf-dirty #69
    Hardware name: /D946GZIS, BIOS TS94610J.86A.0087.2007.1107.1049 11/07/2007
    task: ffff88012a0b4080 task.stack: ffff880123850000
    RIP: 0010:[<ffffffff81003c92>] [<ffffffff81003c92>] x86_perf_event_update+0x52/0xc0
    RSP: 0018:ffff880123853b60 EFLAGS: 00010087
    RAX: 0000000000000001 RBX: ffff88012fc0a3c0 RCX: 000000000000001e
    RDX: 0000000000000000 RSI: 0000000040000000 RDI: ffff88012b014800
    RBP: ffff880123853b88 R08: ffffffffffffffff R09: 0000000000000000
    R10: ffffea0004a012c0 R11: ffffea0004acedc0 R12: ffffffff80000001
    R13: ffff88012b0149c0 R14: ffff88012b014800 R15: 0000000000000018
    FS: 00007f8b155cd700(0000) GS:ffff88012fc00000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f8b155f5000 CR3: 000000012a2d7000 CR4: 00000000000006f0
    Stack:
    ffff88012fc0a3c0 ffff88012b014800 0000000000000004 0000000000000001
    ffff88012fc1b750 ffff880123853bb0 ffffffff81003d59 ffff88012b014800
    ffff88012fc0a3c0 ffff88012b014800 ffff880123853bd8 ffffffff81003e13
    Call Trace:
    [<ffffffff81003d59>] x86_pmu_stop+0x59/0xd0
    [<ffffffff81003e13>] x86_pmu_del+0x43/0x140
    [<ffffffff8111705d>] event_sched_out.isra.105+0xbd/0x260
    [<ffffffff8111738d>] __perf_remove_from_context+0x2d/0xb0
    [<ffffffff8111745d>] __perf_event_exit_context+0x4d/0x70
    [<ffffffff810c8826>] generic_exec_single+0xb6/0x140
    [<ffffffff81117410>] ? __perf_remove_from_context+0xb0/0xb0
    [<ffffffff81117410>] ? __perf_remove_from_context+0xb0/0xb0
    [<ffffffff810c898f>] smp_call_function_single+0xdf/0x140
    [<ffffffff81113d27>] perf_event_exit_cpu_context+0x87/0xc0
    [<ffffffff81113d73>] perf_reboot+0x13/0x40
    [<ffffffff8107578a>] notifier_call_chain+0x4a/0x70
    [<ffffffff81075ad7>] __blocking_notifier_call_chain+0x47/0x60
    [<ffffffff81075b06>] blocking_notifier_call_chain+0x16/0x20
    [<ffffffff81076a1d>] kernel_restart_prepare+0x1d/0x40
    [<ffffffff81076ae2>] kernel_restart+0x12/0x60
    [<ffffffff81076d56>] SYSC_reboot+0xf6/0x1b0
    [<ffffffff811a823c>] ? mntput_no_expire+0x2c/0x1b0
    [<ffffffff811a83e4>] ? mntput+0x24/0x40
    [<ffffffff811894fc>] ? __fput+0x16c/0x1e0
    [<ffffffff811895ae>] ? ____fput+0xe/0x10
    [<ffffffff81072fc3>] ? task_work_run+0x83/0xa0
    [<ffffffff81001623>] ? exit_to_usermode_loop+0x53/0xc0
    [<ffffffff8100105a>] ? trace_hardirqs_on_thunk+0x1a/0x1c
    [<ffffffff81076e6e>] SyS_reboot+0xe/0x10
    [<ffffffff814c4ba5>] entry_SYSCALL_64_fastpath+0x18/0xa3
    Code: 7c 4c 8d af c0 01 00 00 49 89 fe eb 10 48 09 c2 4c 89 e0 49 0f b1 55 00 4c 39 e0 74 35 4d 8b a6 c0 01 00 00 41 8b 8e 60 01 00 00 <0f> 33 8b 35 6e 02 8c 00 48 c1 e2 20 85 f6 7e d2 48 89 d3 89 cf
    RIP [<ffffffff81003c92>] x86_perf_event_update+0x52/0xc0
    RSP <ffff880123853b60>
    ---[ end trace 7ec95181faf211be ]---
    note: reboot[3070] exited with preempt_count 2

    Cc: Borislav Petkov <bp@suse.de>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Andy Lutomirski <luto@amacapital.net>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@kernel.org>
    Fixes: f5967101e9de ("x86/hweight: Get rid of the special calling convention")
    Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
    ---
    arch/x86/lib/hweight.S | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/arch/x86/lib/hweight.S b/arch/x86/lib/hweight.S
    index 02de3d74d2c5..8a602a1e404a 100644
    --- a/arch/x86/lib/hweight.S
    +++ b/arch/x86/lib/hweight.S
    @@ -35,6 +35,7 @@ ENDPROC(__sw_hweight32)

    ENTRY(__sw_hweight64)
    #ifdef CONFIG_X86_64
    + pushq %rdi
    pushq %rdx

    movq %rdi, %rdx # w -> t
    @@ -60,6 +61,7 @@ ENTRY(__sw_hweight64)
    shrq $56, %rax # w = w_tmp >> 56

    popq %rdx
    + popq %rdi
    ret
    #else /* CONFIG_X86_32 */
    /* We're getting an u64 arg in (%eax,%edx): unsigned long hweight64(__u64 w) */
    --
    2.7.4
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