Re: [Qemu-devel] [PATCH] mttcg: Set jmp_env to handle exit from tb_gen_code

[Alex Bennée]

Pranith Kumar <address@hidden> writes:

> tb_gen_code() can exit execution using cpu_exit_loop() when it cannot
> allocate new tb's. To handle this, we need to properly set the jmp_env
> pointer ahead of calling tb_gen_code().
>
> CC:Alex Bennée <address@hidden>
> CC: Richard Henderson <address@hidden>
> Signed-off-by: Pranith Kumar <address@hidden>
> ---
>  cpu-exec.c | 23 +++++++++++------------
>  1 file changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/cpu-exec.c b/cpu-exec.c
> index 97d79612d9..4b70988b24 100644
> --- a/cpu-exec.c
> +++ b/cpu-exec.c
> @@ -236,23 +236,22 @@ static void cpu_exec_step(CPUState *cpu)
>
>      cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
>      tb_lock();
> -    tb = tb_gen_code(cpu, pc, cs_base, flags,
> -                     1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
> -    tb->orig_tb = NULL;
> -    tb_unlock();
> -
> -    cc->cpu_exec_enter(cpu);
> -

It occurs to me we are also diverging in our locking pattern from
tb_find which takes mmap_lock first. This is a NOP for system emulation
but needed for user-emulation (for which we can do cpu_exec_step but not
cpu_exec_nocache).

>      if (sigsetjmp(cpu->jmp_env, 0) == 0) {
> +        tb = tb_gen_code(cpu, pc, cs_base, flags,
> +                         1 | CF_NOCACHE | CF_IGNORE_ICOUNT);
> +        tb->orig_tb = NULL;
> +        tb_unlock();
> +
> +        cc->cpu_exec_enter(cpu);
>          /* execute the generated code */
>          trace_exec_tb_nocache(tb, pc);
>          cpu_tb_exec(cpu, tb);
> -    }
> +        cc->cpu_exec_exit(cpu);
>
> -    cc->cpu_exec_exit(cpu);
> -    tb_lock();
> -    tb_phys_invalidate(tb, -1);
> -    tb_free(tb);
> +        tb_lock();
> +        tb_phys_invalidate(tb, -1);
> +        tb_free(tb);
> +    }
>      tb_unlock();
>  }


--
Alex Bennée