Re: [Qemu-devel] [PATCH] linux-user: Handle new ARM breakpoint instruction

[Peter Maydell <peter.maydell@linaro.org>]

On 25 June 2014 05:08, Hunter Laux <hunterlaux@gmail.com> wrote:
> This instruction space is guaranteed to be undefined.
> ARM:   xxxx 0111 1111 xxxx xxxx xxxx 1111 xxxx
> Thumb: 1101 1110 xxxx xxxx
>
> The breakpoint instructions were selected from this instruction space.
> Linux traps the illegal instruction and sends a SIGTRAP if it is a breakpoint.
>
> Here is the Linux implementation:
> http://lxr.free-electrons.com/source/arch/arm/kernel/ptrace.c#L221
>
> Signed-off-by: Hunter Laux <hunterlaux@gmail.com>
> ---
>  linux-user/main.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/linux-user/main.c b/linux-user/main.c
> index 900a17f..91f2681 100644
> --- a/linux-user/main.c
> +++ b/linux-user/main.c
> @@ -688,11 +688,29 @@ void cpu_loop(CPUARMState *env)
>                  uint32_t opcode;
>                  int rc;
>
> +                const uint32_t arm_bkpt_mask        = 0x0FFFFFFF;
> +                const uint32_t arm_bkpt             = 0x07F001F0;
> +                const uint32_t arm_bkpt_thumb_mask  = 0x0000FFFF;
> +                const uint32_t arm_bkpt_thumb       = 0x0000DE01;
> +                const uint32_t arm_bkpt_thumb2_mask = 0xFFFFFFFF;
> +                const uint32_t arm_bkpt_thumb2      = 0xF7F0A000;
> +
>                  /* we handle the FPU emulation here, as Linux */
>                  /* we get the opcode */
>                  /* FIXME - what to do if get_user() fails? */
>                  get_user_code_u32(opcode, env->regs[15], env->bswap_code);
>
> +                if (env->thumb) {
> +                    if ((opcode & arm_bkpt_thumb_mask) == arm_bkpt_thumb
> +                        || (opcode & arm_bkpt_thumb2_mask) == arm_bkpt_thumb2) {
> +                        goto excp_debug;
> +                    }
> +                } else {
> +                    if ((opcode & arm_bkpt_mask) == arm_bkpt) {
> +                        goto excp_debug;
> +                    }
> +                }
> +
>                  rc = EmulateAll(opcode, &ts->fpa, env);
>                  if (rc == 0) { /* illegal instruction */
>                      info.si_signo = SIGILL;

This shouldn't be necessary, because our instruction decoder
causes the BKPT instructions to generate an EXCP_BKPT
(see target-arm/translate.c). So we should never go through
this code path for these instructions...

thanks
-- PMM