path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2014-12-09 13:12:47 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-09 13:12:47 -0800
commitb64bb1d758163814687eb3b84d74e56f04d0c9d1 (patch)
tree59f1db8b718e98d13c6cf9d3486221cfff6e7eef /Documentation
parentMerge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/geert/linux-m68k (diff)
parentarm64: remove the unnecessary arm64_swiotlb_init() (diff)
Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull arm64 updates from Will Deacon: "Here's the usual mixed bag of arm64 updates, also including some related EFI changes (Acked by Matt) and the MMU gather range cleanup (Acked by you). Changes include: - support for alternative instruction patching from Andre - seccomp from Akashi - some AArch32 instruction emulation, required by the Android folks - optimisations for exception entry/exit code, cmpxchg, pcpu atomics - mmu_gather range calculations moved into core code - EFI updates from Ard, including long-awaited SMBIOS support - /proc/cpuinfo fixes to align with the format used by arch/arm/ - a few non-critical fixes across the architecture" * tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (70 commits) arm64: remove the unnecessary arm64_swiotlb_init() arm64: add module support for alternatives fixups arm64: perf: Prevent wraparound during overflow arm64/include/asm: Fixed a warning about 'struct pt_regs' arm64: Provide a namespace to NCAPS arm64: bpf: lift restriction on last instruction arm64: Implement support for read-mostly sections arm64: compat: align cacheflush syscall with arch/arm arm64: add seccomp support arm64: add SIGSYS siginfo for compat task arm64: add seccomp syscall for compat task asm-generic: add generic seccomp.h for secure computing mode 1 arm64: ptrace: allow tracer to skip a system call arm64: ptrace: add NT_ARM_SYSTEM_CALL regset arm64: Move some head.text functions to executable section arm64: jump labels: NOP out NOP -> NOP replacement arm64: add support to dump the kernel page tables arm64: Add FIX_HOLE to permanent fixed addresses arm64: alternatives: fix pr_fmt string for consistency arm64: vmlinux.lds.S: don't discard .exit.* sections at link-time ...
Diffstat (limited to 'Documentation')
1 files changed, 45 insertions, 0 deletions
diff --git a/Documentation/arm64/legacy_instructions.txt b/Documentation/arm64/legacy_instructions.txt
new file mode 100644
index 000000000000..a3b3da2ec6ed
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+++ b/Documentation/arm64/legacy_instructions.txt
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+The arm64 port of the Linux kernel provides infrastructure to support
+emulation of instructions which have been deprecated, or obsoleted in
+the architecture. The infrastructure code uses undefined instruction
+hooks to support emulation. Where available it also allows turning on
+the instruction execution in hardware.
+The emulation mode can be controlled by writing to sysctl nodes
+(/proc/sys/abi). The following explains the different execution
+behaviours and the corresponding values of the sysctl nodes -
+* Undef
+ Value: 0
+ Generates undefined instruction abort. Default for instructions that
+ have been obsoleted in the architecture, e.g., SWP
+* Emulate
+ Value: 1
+ Uses software emulation. To aid migration of software, in this mode
+ usage of emulated instruction is traced as well as rate limited
+ warnings are issued. This is the default for deprecated
+ instructions, .e.g., CP15 barriers
+* Hardware Execution
+ Value: 2
+ Although marked as deprecated, some implementations may support the
+ enabling/disabling of hardware support for the execution of these
+ instructions. Using hardware execution generally provides better
+ performance, but at the loss of ability to gather runtime statistics
+ about the use of the deprecated instructions.
+The default mode depends on the status of the instruction in the
+architecture. Deprecated instructions should default to emulation
+while obsolete instructions must be undefined by default.
+Supported legacy instructions
+* SWP{B}
+Node: /proc/sys/abi/swp
+Status: Obsolete
+Default: Undef (0)
+* CP15 Barriers
+Node: /proc/sys/abi/cp15_barrier
+Status: Deprecated
+Default: Emulate (1)