| // Copyright 2016 The Fuchsia Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "private.h" |
| |
| #ifdef __x86_64__ |
| #include <x86intrin.h> |
| #endif |
| |
| __EXPORT zx_ticks_t _zx_ticks_get(void) { |
| #if __aarch64__ |
| // read the virtual counter |
| zx_ticks_t ticks; |
| __asm__ volatile("mrs %0, cntvct_el0" : "=r"(ticks)); |
| return ticks; |
| #elif __x86_64__ |
| return __rdtsc(); |
| #else |
| #error Unsupported architecture |
| #endif |
| } |
| |
| #if __aarch64__ |
| // This is a specialized version of zx_ticks_get used to work around Cortex-A73 |
| // erratum 858921 described in: |
| // |
| // https://static.docs.arm.com/epm086451/120/Cortex-A73_MPCore_Software_Developers_Errata_Notice.pdf |
| // |
| // This 2x read technique is the same technique currently being used in the |
| // kernel to mitigate the errata. It will be selected by the kernel during VDSO |
| // construction if needed. |
| VDSO_KERNEL_EXPORT zx_ticks_t CODE_ticks_get_arm_a73(void) { |
| zx_ticks_t ticks1, ticks2; |
| __asm__ volatile("mrs %0, cntvct_el0" : "=r"(ticks1)); |
| __asm__ volatile("mrs %0, cntvct_el0" : "=r"(ticks2)); |
| return (((ticks1 ^ ticks2) >> 32) & 1) ? ticks1 : ticks2; |
| } |
| #endif |
| |
| VDSO_INTERFACE_FUNCTION(zx_ticks_get); |
| |
| // Note: See alternates.ld for a definition of CODE_ticks_get_via_kernel, which |
| // is an alias for SYSCALL_zx_ticks_get_via_kernel. This is a version of |
| // zx_ticks_get which goes through a forced syscall. It is selected by the vDSO |
| // builder at runtime for use on platforms where the hardware tick counter is |
| // not directly accessible by user mode code. |
