Re: [PATCH 3/4] linux-user/arm: Handle invalid arm-specific syscalls correctly

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Mon, Apr 20, 2020 at 10:22:05PM +0100, Peter Maydell wrote:
> The kernel has different handling for syscalls with invalid
> numbers that are in the "arm-specific" range 0x9f0000 and up:
>  * 0x9f0000..0x9f07ff return -ENOSYS if not implemented
>  * other out of range syscalls cause a SIGILL
> (see the kernel's arch/arm/kernel/traps.c:arm_syscall())
> 
> Implement this distinction. (Note that our code doesn't look
> quite like the kernel's, because we have removed the
> 0x900000 prefix by this point, whereas the kernel retains
> it in arm_syscall().)
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/arm/cpu_loop.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/linux-user/arm/cpu_loop.c b/linux-user/arm/cpu_loop.c
> index 025887d6b86..f042108b0be 100644
> --- a/linux-user/arm/cpu_loop.c
> +++ b/linux-user/arm/cpu_loop.c
> @@ -332,10 +332,32 @@ void cpu_loop(CPUARMState *env)
>                              env->regs[0] = cpu_get_tls(env);
>                              break;
>                          default:
> -                            qemu_log_mask(LOG_UNIMP,
> -                                          "qemu: Unsupported ARM syscall: 0x%x\n",
> -                                          n);
> -                            env->regs[0] = -TARGET_ENOSYS;
> +                            if (n < 0xf0800) {
> +                                /*
> +                                 * Syscalls 0xf0000..0xf07ff (or 0x9f0000..
> +                                 * 0x9f07ff in OABI numbering) are defined
> +                                 * to return -ENOSYS rather than raising
> +                                 * SIGILL. Note that we have already
> +                                 * removed the 0x900000 prefix.
> +                                 */
> +                                qemu_log_mask(LOG_UNIMP,
> +                                    "qemu: Unsupported ARM syscall: 0x%x\n",
> +                                              n);
> +                                env->regs[0] = -TARGET_ENOSYS;
> +                            } else {
> +                                /* Otherwise SIGILL */
> +                                info.si_signo = TARGET_SIGILL;
> +                                info.si_errno = 0;
> +                                info.si_code = TARGET_ILL_ILLTRP;
> +                                info._sifields._sigfault._addr = env->regs[15];
> +                                if (env->thumb) {
> +                                    info._sifields._sigfault._addr -= 2;
> +                                } else {
> +                                    info._sifields._sigfault._addr -= 2;
> +                                }


Am I missing some detail or are both branches of the if-else doing the
same thing?

Cheers,
Edgar



> +                                queue_signal(env, info.si_signo,
> +                                             QEMU_SI_FAULT, &info);
> +                            }
>                              break;
>                          }
>                      } else {
> -- 
> 2.20.1
> 
>