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    Subject[patch 20/29] x86: mark read_crX() asm code as volatile
    2.6.23-stable review patch.  If anyone has any objections, please let us
    know.

    ------------------
    From: Kirill Korotaev <dev@openvz.org>

    patch c1217a75ea102d4e69321f210fab60bc47b9a48e in mainline.

    x86: mark read_crX() asm code as volatile

    Some gcc versions (I checked at least 4.1.1 from RHEL5 & 4.1.2 from gentoo)
    can generate incorrect code with read_crX()/write_crX() functions mix up,
    due to cached results of read_crX().

    The small app for x8664 below compiled with -O2 demonstrates this
    (i686 does the same thing):

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    include/asm-i386/system.h | 2 +-
    include/asm-x86_64/system.h | 8 ++++----
    2 files changed, 5 insertions(+), 5 deletions(-)

    --- a/include/asm-i386/system.h
    +++ b/include/asm-i386/system.h
    @@ -141,7 +141,7 @@ static inline unsigned long native_read_
    {
    unsigned long val;
    /* This could fault if %cr4 does not exist */
    - asm("1: movl %%cr4, %0 \n"
    + asm volatile("1: movl %%cr4, %0 \n"
    "2: \n"
    ".section __ex_table,\"a\" \n"
    ".long 1b,2b \n"
    --- a/include/asm-x86_64/system.h
    +++ b/include/asm-x86_64/system.h
    @@ -85,7 +85,7 @@ static inline void write_cr0(unsigned lo
    static inline unsigned long read_cr2(void)
    {
    unsigned long cr2;
    - asm("movq %%cr2,%0" : "=r" (cr2));
    + asm volatile("movq %%cr2,%0" : "=r" (cr2));
    return cr2;
    }

    @@ -97,7 +97,7 @@ static inline void write_cr2(unsigned lo
    static inline unsigned long read_cr3(void)
    {
    unsigned long cr3;
    - asm("movq %%cr3,%0" : "=r" (cr3));
    + asm volatile("movq %%cr3,%0" : "=r" (cr3));
    return cr3;
    }

    @@ -109,7 +109,7 @@ static inline void write_cr3(unsigned lo
    static inline unsigned long read_cr4(void)
    {
    unsigned long cr4;
    - asm("movq %%cr4,%0" : "=r" (cr4));
    + asm volatile("movq %%cr4,%0" : "=r" (cr4));
    return cr4;
    }

    @@ -121,7 +121,7 @@ static inline void write_cr4(unsigned lo
    static inline unsigned long read_cr8(void)
    {
    unsigned long cr8;
    - asm("movq %%cr8,%0" : "=r" (cr8));
    + asm volatile("movq %%cr8,%0" : "=r" (cr8));
    return cr8;
    }

    --
    -
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