| 40 | | */ |
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| 41 | | |
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| 42 | | /** @note |
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| 43 | | * |
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| 44 | | * Some remarks about __volatile__: Without this keyword gcc is allowed to reorder |
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| 45 | | * or even optimize assembler instructions away. For instance, in the following code |
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| 46 | | * the second rdmsr instruction is optimized away because gcc treats that instruction |
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| 47 | | * as deterministic: |
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| 48 | | * |
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| 49 | | * @code |
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| 50 | | * static inline uint64_t rdmsr_low(idx) |
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| 51 | | * { |
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| 52 | | * uint32_t low; |
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| 53 | | * __asm__ ("rdmsr" : "=a"(low) : "c"(idx) : "edx"); |
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| 54 | | * } |
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| 55 | | * ... |
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| 56 | | * uint32_t msr1 = rdmsr(1); |
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| 57 | | * foo(msr1); |
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| 58 | | * msr1 = rdmsr(1); |
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| 59 | | * bar(msr1); |
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| 60 | | * @endcode |
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| 61 | | * |
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| 62 | | * The input parameter of rdmsr_low is the same for both calls and therefore gcc will |
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| 63 | | * use the result of the first call as input parameter for bar() as well. For rdmsr this |
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| 64 | | * is not acceptable as this instruction is _not_ deterministic. This applies to reading |
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| 65 | | * machine status information in general. |
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| | 117 | * @remarks Some remarks about __volatile__: Without this keyword gcc is allowed to reorder |
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| | 118 | * or even optimize assembler instructions away. For instance, in the following code |
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| | 119 | * the second rdmsr instruction is optimized away because gcc treats that instruction |
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| | 120 | * as deterministic: |
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| | 121 | * |
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| | 122 | * @code |
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| | 123 | * static inline uint64_t rdmsr_low(int idx) |
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| | 124 | * { |
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| | 125 | * uint32_t low; |
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| | 126 | * __asm__ ("rdmsr" : "=a"(low) : "c"(idx) : "edx"); |
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| | 127 | * } |
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| | 128 | * ... |
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| | 129 | * uint32_t msr1 = rdmsr_low(1); |
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| | 130 | * foo(msr1); |
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| | 131 | * msr1 = rdmsr_low(1); |
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| | 132 | * bar(msr1); |
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| | 133 | * @endcode |
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| | 134 | * |
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| | 135 | * The input parameter of rdmsr_low is the same for both calls and therefore gcc will |
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| | 136 | * use the result of the first call as input parameter for bar() as well. For rdmsr this |
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| | 137 | * is not acceptable as this instruction is _not_ deterministic. This applies to reading |
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| | 138 | * machine status information in general. |
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| | 139 | * |
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