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27 lines
1.2 KiB
27 lines
1.2 KiB
Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE) |
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ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommeds |
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moving to the load-locked/store-conditional instructions LDREX and STREX. |
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ARMv7 multiprocessing extensions introduce the ability to disable these |
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instructions, triggering an undefined instruction exception when executed. |
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Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB |
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sequence. If a memory access fault (an abort) occurs, a segmentation fault is |
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signalled to the triggering process. |
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/proc/cpu/swp_emulation holds some statistics/information, including the PID of |
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the last process to trigger the emulation to be invocated. For example:: |
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Emulated SWP: 12 |
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Emulated SWPB: 0 |
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Aborted SWP{B}: 1 |
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Last process: 314 |
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NOTE: |
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when accessing uncached shared regions, LDREX/STREX rely on an external |
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transaction monitoring block called a global monitor to maintain update |
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atomicity. If your system does not implement a global monitor, this option can |
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cause programs that perform SWP operations to uncached memory to deadlock, as |
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the STREX operation will always fail.
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