e72e9355e3
git: https://android.googlesource.com/kernel/common branch: android-4.9 commit: 03fcc2fe71308c2d164b4e6cbfc738c63e670444
28 lines
1.2 KiB
Plaintext
28 lines
1.2 KiB
Plaintext
Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
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---------------------------------------------------------------------
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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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---
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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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---
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NOTE: 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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