Re: [PATCH v4 07/43] tcg: Add in_code_gen_buffer

[Philippe Mathieu-Daudé]

On 12/14/20 3:02 PM, Richard Henderson wrote:
> Create a function to determine if a pointer is within the buffer.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  include/tcg/tcg.h         |  6 ++++++
>  accel/tcg/translate-all.c | 26 ++++++++------------------
>  2 files changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/include/tcg/tcg.h b/include/tcg/tcg.h
> index bb1e97b13b..e4d0ace44b 100644
> --- a/include/tcg/tcg.h
> +++ b/include/tcg/tcg.h
> @@ -680,6 +680,12 @@ extern __thread TCGContext *tcg_ctx;
>  extern void *tcg_code_gen_epilogue;
>  extern TCGv_env cpu_env;
>  
> +static inline bool in_code_gen_buffer(const void *p)
> +{
> +    const TCGContext *s = &tcg_init_ctx;
> +    return (size_t)(p - s->code_gen_buffer) <= s->code_gen_buffer_size;

If 'p == s->code_gen_buffer + s->code_gen_buffer_size',
is it really "in" the buffer?

> +}
> +
>  static inline size_t temp_idx(TCGTemp *ts)
>  {
>      ptrdiff_t n = ts - tcg_ctx->temps;
> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
> index 4572b4901f..744f97a717 100644
> --- a/accel/tcg/translate-all.c
> +++ b/accel/tcg/translate-all.c
> @@ -392,27 +392,18 @@ void tb_destroy(TranslationBlock *tb)
>  
>  bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc, bool will_exit)
>  {
> -    TranslationBlock *tb;
> -    bool r = false;
> -    uintptr_t check_offset;
> -
> -    /* The host_pc has to be in the region of current code buffer. If
> -     * it is not we will not be able to resolve it here. The two cases
> -     * where host_pc will not be correct are:
> +    /*
> +     * The host_pc has to be in the region of the code buffer.
> +     * If it is not we will not be able to resolve it here.
> +     * The two cases where host_pc will not be correct are:
>       *
>       *  - fault during translation (instruction fetch)
>       *  - fault from helper (not using GETPC() macro)
>       *
>       * Either way we need return early as we can't resolve it here.
> -     *
> -     * We are using unsigned arithmetic so if host_pc <
> -     * tcg_init_ctx.code_gen_buffer check_offset will wrap to way
> -     * above the code_gen_buffer_size
>       */
> -    check_offset = host_pc - (uintptr_t) tcg_init_ctx.code_gen_buffer;
> -
> -    if (check_offset < tcg_init_ctx.code_gen_buffer_size) {
> -        tb = tcg_tb_lookup(host_pc);
> +    if (in_code_gen_buffer((const void *)host_pc)) {
> +        TranslationBlock *tb = tcg_tb_lookup(host_pc);
>          if (tb) {
>              cpu_restore_state_from_tb(cpu, tb, host_pc, will_exit);
>              if (tb_cflags(tb) & CF_NOCACHE) {
> @@ -421,11 +412,10 @@ bool cpu_restore_state(CPUState *cpu, uintptr_t 
> host_pc, bool will_exit)
>                  tcg_tb_remove(tb);
>                  tb_destroy(tb);
>              }
> -            r = true;
> +            return true;
>          }
>      }
> -
> -    return r;
> +    return false;
>  }
>  
>  static void page_init(void)
>