Re: [Qemu-devel] [PATCH] target/xtensa: linux-user: add call0 ABI support

[Laurent Vivier]

Le 26/08/2019 à 00:17, Max Filippov a écrit :
> Xtensa binaries built for call0 ABI don't rotate register window on
> function calls and returns. Invocation of signal handlers from the
> kernel is therefore different in windowed and call0 ABIs.
> There's currently no way to determine xtensa ELF binary ABI from the
> binary itself. Provide an environment variable QEMU_XTENSA_ABI_CALL0 and
> use it to initialize PS.WOE in xtensa_cpu_reset. Check this flag in
> setup_rt_frame to determine how a signal should be delivered.
> 
> Signed-off-by: Max Filippov <address@hidden>
> ---
>  linux-user/xtensa/signal.c | 25 +++++++++++++++++--------
>  target/xtensa/cpu.c        | 22 ++++++++++++++++++----
>  2 files changed, 35 insertions(+), 12 deletions(-)
> 
> diff --git a/linux-user/xtensa/signal.c b/linux-user/xtensa/signal.c
> index 8d54ef3ae34b..590f0313ffe9 100644
> --- a/linux-user/xtensa/signal.c
> +++ b/linux-user/xtensa/signal.c
> @@ -134,6 +134,8 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
>      abi_ulong frame_addr;
>      struct target_rt_sigframe *frame;
>      uint32_t ra;
> +    bool abi_call0;
> +    unsigned base;
>      int i;
>  
>      frame_addr = get_sigframe(ka, env, sizeof(*frame));
> @@ -182,20 +184,27 @@ void setup_rt_frame(int sig, struct target_sigaction 
> *ka,
>          __put_user(0x00, &frame->retcode[5]);
>  #endif
>      }
> -    env->sregs[PS] = PS_UM | (3 << PS_RING_SHIFT);
> -    if (xtensa_option_enabled(env->config, XTENSA_OPTION_WINDOWED_REGISTER)) 
> {
> -        env->sregs[PS] |= PS_WOE | (1 << PS_CALLINC_SHIFT);
> -    }
>      memset(env->regs, 0, sizeof(env->regs));
>      env->pc = ka->_sa_handler;
>      env->regs[1] = frame_addr;
>      env->sregs[WINDOW_BASE] = 0;
>      env->sregs[WINDOW_START] = 1;
>  
> -    env->regs[4] = (ra & 0x3fffffff) | 0x40000000;
> -    env->regs[6] = sig;
> -    env->regs[7] = frame_addr + offsetof(struct target_rt_sigframe, info);
> -    env->regs[8] = frame_addr + offsetof(struct target_rt_sigframe, uc);
> +    abi_call0 = (env->sregs[PS] & PS_WOE) == 0;

Is this safe to rely on content of sregs[PS]?
Why don't you use xtensa_abi_call0()?

> +    env->sregs[PS] = PS_UM | (3 << PS_RING_SHIFT);
> +
> +    if (abi_call0) {
> +        base = 0;
> +        env->regs[base] = ra;
> +    } else {
> +        env->sregs[PS] |= PS_WOE | (1 << PS_CALLINC_SHIFT);
> +        base = 4;
> +        env->regs[base] = (ra & 0x3fffffff) | 0x40000000;
> +    }
> +    env->regs[base + 2] = sig;
> +    env->regs[base + 3] = frame_addr + offsetof(struct target_rt_sigframe,
> +                                                info);
> +    env->regs[base + 4] = frame_addr + offsetof(struct target_rt_sigframe, 
> uc);
>      unlock_user_struct(frame, frame_addr, 1);
>      return;
>  
> diff --git a/target/xtensa/cpu.c b/target/xtensa/cpu.c
> index 76db1741a796..791c061880e7 100644
> --- a/target/xtensa/cpu.c
> +++ b/target/xtensa/cpu.c
> @@ -53,6 +53,18 @@ static bool xtensa_cpu_has_work(CPUState *cs)
>  #endif
>  }
>  
> +#ifdef CONFIG_USER_ONLY
> +static int xtensa_abi_call0(void)
> +{
> +    static int abi_call0 = -1;
> +
> +    if (abi_call0 == -1) {
> +        abi_call0 = getenv("QEMU_XTENSA_ABI_CALL0") != NULL;

Wouldn't it be cleaner to add this in the arg_table[] in
linux-user/main.c and then use directly the variable?

Thanks,
Laurent