Le 16/06/2016 à 21:15, Pranith Kumar a écrit :
> On Thu, Jun 16, 2016 at 3:07 PM, Richard Henderson <r...@twiddle.net> wrote:
>> 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.pr...@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.
>
> If you see line 2 of the condition you check for (addr < 0). Only if
> this evaluates to true do you check the right shift value of addr.
>
> Reg. (2), I think that is what gcc is erroring out for.
> TARGET_VIRT_ADDR_SPACE_BITS is 63 for linux-user and we are comparing
> (addr >> 63) with itself. GCC rightly says that it is a tautological
> compare and errors out. May be we can have a better work around.
Perhaps something like:
#ifndef CONFIG_USER_ONLY
static bool in_superpage(DisasContext *ctx, int64_t addr)
{
...
}
#endif
...
#ifdef CONFIG_USER_ONLY
pc_mask = ~TARGET_PAGE_MASK;
#else
if (in_superpage(&ctx, pc_start)) {
pc_mask = (1ULL << 41) - 1;
} else {
pc_mask = ~TARGET_PAGE_MASK;
}
#endif
Laurent
