Re: [PATCH] target/arm: Fix reads of CNTFRQ_EL0 in linux-user mode

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 13/10/25 18:10, Peter Maydell wrote:
> In commit bd8e9ddf6f6 ("target/arm: Refactor default generic timer
> frequency handling") we changed how we initialized the generic timer
> frequency as reported in the CNTFRQ_EL0 register.  As part of that,
> we chanegd the linux-user version of the CNTFRQ_EL0 sysreg from

"changed"

> having a constant value set at compile time through the .resetvalue
> field to having a reset value which we compute in a .resetfn.
> 
> This accidentally broke the reading of CNTFRQ_EL0 in linux-user mode,
> because the cpreg is marked as ARM_CP_CONST, which means we translate
> it as a read of the compile-time constant value in the .resetvalue
> field.  This is now zero, so userspace sees a 0 frequency value.
> 
> Fix the bug by dropping the ARM_CP_CONST marking.  This will cause us
> to translate the read as a load of the value from the CPU state
> struct cp15.c14_cntfrq field, which is where the real frequency value
> now lives.
> 
> Cc: qemu-stable@nongnu.org
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3159
> Fixes: bd8e9ddf6f6 ("target/arm: Refactor default generic timer frequency handling")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   target/arm/helper.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>