Since kernel commit a86bd139f2 (arm64: arch_timer: Enable CNTVCT_EL0 trap..) user-space has been able to read this system register. This patch enables access to that register although currently it always returns 0 as we don't yet have a mechanism for managing timers in linux-user mode.
Signed-off-by: Alex Bennée <alex.ben...@linaro.org> --- target/arm/helper.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/target/arm/helper.c b/target/arm/helper.c index b14fdab140..8244badd63 100644 --- a/target/arm/helper.c +++ b/target/arm/helper.c @@ -2121,11 +2121,25 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[] = { }; #else -/* In user-mode none of the generic timer registers are accessible, - * and their implementation depends on QEMU_CLOCK_VIRTUAL and qdev gpio outputs, - * so instead just don't register any of them. + +/* In user-mode most of the generic timer registers are inaccessible + * however modern kernels (4.12+) allow access to cntvct_el0 */ + +static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri) +{ + /* Currently we have no support for QEMUTimer in linux-user so we + * can't call gt_get_countervalue(env). + */ + return 0; +} + static const ARMCPRegInfo generic_timer_cp_reginfo[] = { + { .name = "CNTVCT_EL0", .state = ARM_CP_STATE_AA64, + .opc0 = 3, .opc1 = 3, .crn = 14, .crm = 0, .opc2 = 2, + .access = PL0_R, .type = ARM_CP_NO_RAW | ARM_CP_IO, + .readfn = gt_virt_cnt_read, + }, REGINFO_SENTINEL }; -- 2.17.0