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    SubjectRe: [tip:x86/alternatives] x86, alternatives: Use 16-bit numbers for cpufeature index
    tip-bot for H. Peter Anvin wrote:
    > Commit-ID: f88731e3068f9d1392ba71cc9f50f035d26a0d4f
    > Gitweb: http://git.kernel.org/tip/f88731e3068f9d1392ba71cc9f50f035d26a0d4f
    > Author: H. Peter Anvin <hpa@linux.intel.com>
    > AuthorDate: Wed, 9 Jun 2010 16:03:09 -0700
    > Committer: H. Peter Anvin <hpa@linux.intel.com>
    > CommitDate: Wed, 9 Jun 2010 16:03:09 -0700
    >
    > x86, alternatives: Use 16-bit numbers for cpufeature index
    >
    > We already have cpufeature indicies above 255, so use a 16-bit number
    > for the alternatives index. This consumes a padding field and so
    > doesn't add any size, but it means that abusing the padding field to
    > create assembly errors on overflow no longer works. We can retain the
    > test simply by redirecting it to the .discard section, however.
    >

    My machine hits "invalid opcode" at *prepare_to_copy+0x79,
    and it can't boot up.

    (gdb) l *prepare_to_copy+0x79
    0xc0101789 is in prepare_to_copy (/home/njubee/work/linux-2.6-tip/arch/x86/include/asm/xsave.h:118).
    113
    114 static inline void fpu_xsave(struct fpu *fpu)
    115 {
    116 /* This, however, we can work around by forcing the compiler to select
    117 an addressing mode that doesn't require extended registers. */
    118 __asm__ __volatile__(".byte " REX_PREFIX "0x0f,0xae,0x27"
    119 : : "D" (&(fpu->state->xsave)),
    120 "a" (-1), "d"(-1) : "memory");
    121 }
    122 #endif

    It can boot up if this patch is reverted.
    Does this patch change the return value of "use_xsave()"

    cat /proc/cpuinfo
    processor : 0
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Pentium(R) D CPU 2.80GHz
    stepping : 8
    cpu MHz : 2800.120
    cache size : 1024 KB
    fdiv_bug : no
    hlt_bug : no
    f00f_bug : no
    coma_bug : no
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss constant_tsc pebs bts tsc_reliable pni ds_cpl
    bogomips : 5600.24
    clflush size : 64
    cache_alignment : 128
    address sizes : 36 bits physical, 48 bits virtual
    power management:

    processor : 1
    vendor_id : GenuineIntel
    cpu family : 15
    model : 4
    model name : Intel(R) Pentium(R) D CPU 2.80GHz
    stepping : 8
    cpu MHz : 2800.120
    cache size : 1024 KB
    fdiv_bug : no
    hlt_bug : no
    f00f_bug : no
    coma_bug : no
    fpu : yes
    fpu_exception : yes
    cpuid level : 5
    wp : yes
    flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss constant_tsc pebs bts tsc_reliable pni ds_cpl
    bogomips : 5574.36
    clflush size : 64
    cache_alignment : 128
    address sizes : 36 bits physical, 48 bits virtual
    power management:


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