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From: Richard Henderson <rth@twiddle.net>
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Date: Thu, 16 Jun 2016 12:07:40 -0700
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Subject: Re: [Qemu-devel] [PATCH] alpha: Fix build error for linux-user
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To: Pranith Kumar <bobby.prani@gmail.com>, "open list:All patches CC here" <qemu-devel@nongnu.org>

On 06/16/2016 11:56 AM, Pranith Kumar wrote:
> Using gcc 6.1 for alpha-linux-user target we see the following build
> error:
> 
> /mnt/devops/code/qemu/target-alpha/translate.c: In function ‘in_superpage’:
> /mnt/devops/code/qemu/target-alpha/translate.c:454:52: error: self-comparison always evaluates to true [-Werror=tautological-compare]
>              && addr >> TARGET_VIRT_ADDR_SPACE_BITS == addr >> 63);
> 
> Fix it by replacing (addr >> 63) by '1' which is what it evaluates to
> since addr is negative.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> ---
>  target-alpha/translate.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/target-alpha/translate.c b/target-alpha/translate.c
> index f9b2426..31da6ea 100644
> --- a/target-alpha/translate.c
> +++ b/target-alpha/translate.c
> @@ -451,7 +451,7 @@ static bool in_superpage(DisasContext *ctx, int64_t addr)
>      return ((ctx->tb->flags & TB_FLAGS_USER_MODE) == 0
>              && addr < 0
>              && ((addr >> 41) & 3) == 2
> -            && addr >> TARGET_VIRT_ADDR_SPACE_BITS == addr >> 63);
> +            && addr >> TARGET_VIRT_ADDR_SPACE_BITS == 1);
>  }

This fix is incorrect.

  (1) addr is not always negative.
  (2) in_superpage is only relevant for alpha-softmmu, where
      TARGET_VIRT_ADDR_SPACE_BITS is not 63.


r~