Re: [PATCH v2 1/3] tcg/sparc: Fix temp_allocate_frame vs sparc stack bias

[Philippe Mathieu-Daudé]

On 6/19/21 3:42 PM, Richard Henderson wrote:
> We should not be aligning the offset in temp_allocate_frame,
> because the odd offset produces an aligned address in the end.
> Instead, pass the logical offset into tcg_set_frame and add
> the stack bias last.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/tcg.c                  |  9 +++------
>  tcg/sparc/tcg-target.c.inc | 16 ++++++++++------
>  2 files changed, 13 insertions(+), 12 deletions(-)

LGTM but I'd rather have another review...

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

> diff --git a/tcg/tcg.c b/tcg/tcg.c
> index dd584f3bba..52e858523c 100644
> --- a/tcg/tcg.c
> +++ b/tcg/tcg.c
> @@ -3015,17 +3015,14 @@ static void check_regs(TCGContext *s)
>  
>  static void temp_allocate_frame(TCGContext *s, TCGTemp *ts)
>  {
> -#if !(defined(__sparc__) && TCG_TARGET_REG_BITS == 64)
> -    /* Sparc64 stack is accessed with offset of 2047 */
> -    s->current_frame_offset = (s->current_frame_offset +
> -                               (tcg_target_long)sizeof(tcg_target_long) - 1) 
> &
> -        ~(sizeof(tcg_target_long) - 1);
> -#endif
>      if (s->current_frame_offset + (tcg_target_long)sizeof(tcg_target_long) >
>          s->frame_end) {
>          tcg_abort();
>      }
>      ts->mem_offset = s->current_frame_offset;
> +#if defined(__sparc__)
> +    ts->mem_offset += TCG_TARGET_STACK_BIAS;
> +#endif
>      ts->mem_base = s->frame_temp;
>      ts->mem_allocated = 1;
>      s->current_frame_offset += sizeof(tcg_target_long);
> diff --git a/tcg/sparc/tcg-target.c.inc b/tcg/sparc/tcg-target.c.inc
> index ce39ac2d86..a6ec94a094 100644
> --- a/tcg/sparc/tcg-target.c.inc
> +++ b/tcg/sparc/tcg-target.c.inc
> @@ -984,14 +984,18 @@ static void tcg_target_qemu_prologue(TCGContext *s)
>  {
>      int tmp_buf_size, frame_size;
>  
> -    /* The TCG temp buffer is at the top of the frame, immediately
> -       below the frame pointer.  */
> +    /*
> +     * The TCG temp buffer is at the top of the frame, immediately
> +     * below the frame pointer.  Use the logical (aligned) offset here;
> +     * the stack bias is applied in temp_allocate_frame().
> +     */
>      tmp_buf_size = CPU_TEMP_BUF_NLONGS * (int)sizeof(long);
> -    tcg_set_frame(s, TCG_REG_I6, TCG_TARGET_STACK_BIAS - tmp_buf_size,
> -                  tmp_buf_size);
> +    tcg_set_frame(s, TCG_REG_I6, -tmp_buf_size, tmp_buf_size);
>  
> -    /* TCG_TARGET_CALL_STACK_OFFSET includes the stack bias, but is
> -       otherwise the minimal frame usable by callees.  */
> +    /*
> +     * TCG_TARGET_CALL_STACK_OFFSET includes the stack bias, but is
> +     * otherwise the minimal frame usable by callees.
> +     */
>      frame_size = TCG_TARGET_CALL_STACK_OFFSET - TCG_TARGET_STACK_BIAS;
>      frame_size += TCG_STATIC_CALL_ARGS_SIZE + tmp_buf_size;
>      frame_size += TCG_TARGET_STACK_ALIGN - 1;
>