diff options
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. |