Re: [PATCH 7/7] linux-user: limit check to HOST_LONG_BITS < TARGET_ABI_BITS

From: "Alex Bennée" <alex.bennee@linaro.org>
To: Thomas Huth <thuth@redhat.com>
Cc: "Laurent Vivier" <laurent@vivier.eu>,
	"Wainer dos Santos Moschetta" <wainersm@redhat.com>,
	qemu-devel@nongnu.org, "Cleber Rosa" <crosa@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Richard Henderson" <rth@twiddle.net>
Subject: Re: [PATCH 7/7] linux-user: limit check to HOST_LONG_BITS < TARGET_ABI_BITS
Date: Thu, 28 May 2020 09:31:55 +0100	[thread overview]
Message-ID: <87y2pc4g04.fsf@linaro.org> (raw)
In-Reply-To: <037520b7-e17d-b516-a2da-a41ee8a1624a@redhat.com>

Thomas Huth <thuth@redhat.com> writes:

> On 27/05/2020 18.36, Alex Bennée wrote:
>> 
>> Thomas Huth <thuth@redhat.com> writes:
>> 
>>> On 27/05/2020 16.44, Laurent Vivier wrote:
>>>> Le 25/05/2020 à 15:18, Thomas Huth a écrit :
>>>>> From: Alex Bennée <alex.bennee@linaro.org>
>>>>>
>>>>> Newer clangs rightly spot that you can never exceed the full address
>>>>> space of 64 bit hosts with:
>>>>>
>>>>>   linux-user/elfload.c:2076:41: error: result of comparison 'unsigned
>>>>>   long' > 18446744073709551615 is always false
>>>>>   [-Werror,-Wtautological-type-limit-compare]
>>>>>   4685         if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>>>>>   4686             ~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
>>>>>   4687 1 error generated.
>>>>>
>>>>> So lets limit the check to 32 bit hosts only.
>>>>>
>>>>> Fixes: ee94743034bf
>>>>> Reported-by: Thomas Huth <thuth@redhat.com>
>>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>>> [thuth: Use HOST_LONG_BITS < TARGET_ABI_BITS instead of HOST_LONG_BITS == 32]
>>>>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>>>>> ---
>>>>>  linux-user/elfload.c | 2 ++
>>>>>  1 file changed, 2 insertions(+)
>>>>>
>>>>> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
>>>>> index 01a9323a63..ebc663ea0b 100644
>>>>> --- a/linux-user/elfload.c
>>>>> +++ b/linux-user/elfload.c
>>>>> @@ -2073,12 +2073,14 @@ static void pgb_have_guest_base(const char *image_name, abi_ulong guest_loaddr,
>>>>>              exit(EXIT_FAILURE);
>>>>>          }
>>>>>      } else {
>>>>> +#if HOST_LONG_BITS < TARGET_ABI_BITS
>>>>>          if ((guest_hiaddr - guest_base) > ~(uintptr_t)0) {
>>>>>              error_report("%s: requires more virtual address space "
>>>>>                           "than the host can provide (0x%" PRIx64 ")",
>>>>>                           image_name, (uint64_t)guest_hiaddr - guest_base);
>>>>>              exit(EXIT_FAILURE);
>>>>>          }
>>>>> +#endif
>>>>>      }
>>>>>  
>>>>>      /*
>>>>>
>>>>
>>>> Philippe sent the same patch:
>>>>
>>>> https://www.mail-archive.com/qemu-devel@nongnu.org/msg699796.html
>>>
>>> Indeed, but looking more closely, he's using slightly different
>>> locations for the #if and #endif ... not sure what's better though...?
>> 
>> Richard was more inclined to suppress the warning:
>> 
>>   Subject: Re: [PATCH v2] linux-user: limit check to HOST_LONG_BITS == 32
>>   From: Richard Henderson <richard.henderson@linaro.org>
>>   Message-ID: <3069bc1b-115d-f361-8271-c775bf6957ea@linaro.org>
>>   Date: Thu, 21 May 2020 20:15:51 -0700
>> 
>> One reason I dropped the f32 patch from my last PR was because this
>> wasn't the only warning the latest clang picks up.
>
> ... but this is currently the only spot that is required to get the
> gitlab CI going again, so I think we should include this patch until we
> have a final decision whether to disable the warning or not (and we can
> still revert this patch after we disabled the warning). Ok?

I'm certainly happy with that if it gets gitlab working.

My experience with make docker-test-vlang@fedora (with 32) was there
where more things to fix. I guess gitlab didn't trigger them.

-- 
Alex Bennée