xnu-4570.1.46.tar.gz

[apple/xnu.git] / libsyscall / wrappers / mach_continuous_time.c

diff --git a/libsyscall/wrappers/mach_continuous_time.c b/libsyscall/wrappers/mach_continuous_time.c
index 4f20664f8c12924c371d30fb40073432b80b76a1..61b996de70fac6ff24abfa669eddf8a6460f125f 100644 (file)
--- a/libsyscall/wrappers/mach_continuous_time.c
+++ b/libsyscall/wrappers/mach_continuous_time.c
@@ -36,7 +36,9 @@ _mach_continuous_time_base(void)
                volatile uint64_t *base_ptr = (volatile uint64_t*)_COMM_PAGE_CONT_TIMEBASE;
                uint64_t read1, read2;
                read1 = *base_ptr;
-#if   defined(__i386__)
+#if defined(__arm__)
+               __asm__ volatile("dsb sy" ::: "memory");
+#elif defined(__i386__)
                __asm__ volatile("lfence" ::: "memory");
 #else
 #error "unsupported arch"
@@ -51,6 +53,21 @@ _mach_continuous_time_base(void)
 #endif // 64-bit
 }
 
+__attribute__((visibility("hidden")))
+kern_return_t
+_mach_continuous_hwclock(uint64_t *cont_time __unused)
+{
+#if defined(__arm64__)
+       uint8_t cont_hwclock = *((uint8_t*)_COMM_PAGE_CONT_HWCLOCK);
+       uint64_t timebase;
+       if (cont_hwclock) {
+               __asm__ volatile("isb\n" "mrs %0, CNTPCT_EL0" : "=r"(timebase));
+               *cont_time = timebase;
+               return KERN_SUCCESS;
+       }
+#endif
+       return KERN_NOT_SUPPORTED;
+}
 
 __attribute__((visibility("hidden")))
 kern_return_t
@@ -63,6 +80,13 @@ _mach_continuous_time(uint64_t* absolute_time, uint64_t* cont_time)
        do {
         read1 = *base_ptr;
         absolute = mach_absolute_time();
+#if    defined(__arm__) || defined(__arm64__)
+            /*
+             * mach_absolute_time() contains an instruction barrier which will
+             * prevent the speculation of read2 above this point, so we don't
+             * need another barrier here.
+             */
+#endif
                read2 = *base_ptr;
        } while (__builtin_expect((read1 != read2), 0));
 
@@ -76,17 +100,18 @@ uint64_t
 mach_continuous_time(void)
 {
        uint64_t cont_time;
-    _mach_continuous_time(NULL, &cont_time);
+       if (_mach_continuous_hwclock(&cont_time) != KERN_SUCCESS)
+               _mach_continuous_time(NULL, &cont_time);
        return cont_time;
 }
 
 uint64_t
 mach_continuous_approximate_time(void)
 {
-    /*
-     * No retry loop here because if we use a slightly too old timebase that's
-     * okay, we are approximate time anyway.
-     */
-    volatile register uint64_t time_base = _mach_continuous_time_base();
-    return time_base + mach_approximate_time();
+       /*
+        * No retry loop here because if we use a slightly too old timebase that's
+        * okay, we are approximate time anyway.
+       */
+       volatile register uint64_t time_base = _mach_continuous_time_base();
+       return time_base + mach_approximate_time();
 }