diff options
| author | Cherry Zhang <cherryyz@google.com> | 2018-02-12 15:27:02 -0500 |
|---|---|---|
| committer | Cherry Zhang <cherryyz@google.com> | 2018-05-03 21:35:01 +0000 |
| commit | 1b6fec862cbe890ef0abea99827a587ffbe2e0f1 (patch) | |
| tree | 89f6499fff153fc963057b04efce44d9c65829ca /src/runtime/internal/atomic/sys_linux_arm.s | |
| parent | 4a1baf8bd11c8804a22aa8364028ce8d81b6e1f3 (diff) | |
| download | go-1b6fec862cbe890ef0abea99827a587ffbe2e0f1.tar.xz | |
sync/atomic: redirect many functions to runtime/internal/atomic
The implementation of atomics are inherently tricky. It would
be good to have them implemented in a single place, instead of
multiple copies.
Mostly a simple redirect.
On 386, some functions in sync/atomic have better implementations,
which are moved to runtime/internal/atomic.
On ARM, some functions in sync/atomic have better implementations.
They are dropped by this CL, but restored with an improved
version in a follow-up CL. On linux/arm, 64-bit CAS kernel helper
is dropped, as we're trying to move away from kernel helpers.
Fixes #23778.
Change-Id: Icb9e1039acc92adbb2a371c34baaf0b79551c3ea
Reviewed-on: https://go-review.googlesource.com/93637
Reviewed-by: Austin Clements <austin@google.com>
Diffstat (limited to 'src/runtime/internal/atomic/sys_linux_arm.s')
| -rw-r--r-- | src/runtime/internal/atomic/sys_linux_arm.s | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/src/runtime/internal/atomic/sys_linux_arm.s b/src/runtime/internal/atomic/sys_linux_arm.s index 1d6439a6ba..60f28e7216 100644 --- a/src/runtime/internal/atomic/sys_linux_arm.s +++ b/src/runtime/internal/atomic/sys_linux_arm.s @@ -4,8 +4,23 @@ #include "textflag.h" -// Use kernel version instead of native armcas in asm_arm.s. -// See ../../../sync/atomic/asm_linux_arm.s for details. +// Linux/ARM atomic operations. + +// Because there is so much variation in ARM devices, +// the Linux kernel provides an appropriate compare-and-swap +// implementation at address 0xffff0fc0. Caller sets: +// R0 = old value +// R1 = new value +// R2 = addr +// LR = return address +// The function returns with CS true if the swap happened. +// http://lxr.linux.no/linux+v2.6.37.2/arch/arm/kernel/entry-armv.S#L850 +// On older kernels (before 2.6.24) the function can incorrectly +// report a conflict, so we have to double-check the compare ourselves +// and retry if necessary. +// +// http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=b49c0f24cf6744a3f4fd09289fe7cade349dead5 +// TEXT cas<>(SB),NOSPLIT,$0 MOVW $0xffff0fc0, R15 // R15 is hardware PC. |