Re: [Qemu-devel] [PATCH 10/10] armv7m: R14 should reset to 0xffffffff

[Alex Bennée]

Peter Maydell <address@hidden> writes:

> For M profile (unlike A profile) the reset value of R14 is specified
> as 0xffffffff.  (The rationale is that this is an illegal exception
> return value, so if guest code tries to return to it it will result
> in a helpful exception.)
>
> Registers r0 to r12 and the flags are architecturally UNKNOWN on
> reset, so we leave those at zero.
>
> Signed-off-by: Peter Maydell <address@hidden>

Reviewed-by: Alex Bennée <address@hidden>

> ---
>  target/arm/cpu.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
> index 0814f73..e9f10f7 100644
> --- a/target/arm/cpu.c
> +++ b/target/arm/cpu.c
> @@ -196,6 +196,9 @@ static void arm_cpu_reset(CPUState *s)
>           */
>          env->v7m.ccr = R_V7M_CCR_STKALIGN_MASK;
>
> +        /* Unlike A/R profile, M profile defines the reset LR value */
> +        env->regs[14] = 0xffffffff;
> +
>          /* Load the initial SP and PC from the vector table at address 0 */
>          rom = rom_ptr(0);
>          if (rom) {


--
Alex Bennée