From 05115a77e012331b6ff5e24bab40e75848447c62 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?R=C3=A9mi=20Denis-Courmont?= Date: Tue, 15 Aug 2023 18:16:42 +0300 Subject: [PATCH] lavu/timer: use time for AV_READ_TIME on RISC-V So far, AV_READ_TIME would return the cycle counter. This posed two problems: 1) On recent systems, it would just raise an illegal instruction exception. Indeed RDCYCLE is blocked in user space to ward off some side channel attacks. In particular, this would cause the random number generator to crash. 2) It does not match the x86 behaviour and the apparent original intent of AV_READ_TIME in the functional code base (outside test cases). So this replaces the cycle counter with the time counter. The unit is a platform-dependent constant fraction of time, and the value should be stable across harts (RISC-V lingo for physical CPU thread). --- libavutil/riscv/timer.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/libavutil/riscv/timer.h b/libavutil/riscv/timer.h index a34157a566..c2465a4524 100644 --- a/libavutil/riscv/timer.h +++ b/libavutil/riscv/timer.h @@ -24,21 +24,21 @@ #if HAVE_INLINE_ASM #include -static inline uint64_t rdcycle64(void) +static inline uint64_t ff_read_time(void) { #if (__riscv_xlen >= 64) uintptr_t cycles; - __asm__ volatile ("rdcycle %0" : "=r"(cycles)); + __asm__ volatile ("rdtime %0" : "=r" (cycles)); #else uint64_t cycles; uint32_t hi, lo, check; __asm__ volatile ( - "1: rdcycleh %0\n" - " rdcycle %1\n" - " rdcycleh %2\n" + "1: rdtimeh %0\n" + " rdtime %1\n" + " rdtimeh %2\n" " bne %0, %2, 1b\n" : "=r" (hi), "=r" (lo), "=r" (check)); cycles = (((uint64_t)hi) << 32) | lo; @@ -47,7 +47,7 @@ static inline uint64_t rdcycle64(void) return cycles; } -#define AV_READ_TIME rdcycle64 +#define AV_READ_TIME ff_read_time #endif #endif /* AVUTIL_RISCV_TIMER_H */