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

From: Thomas Huth <thuth@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
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 08:45:51 +0200	[thread overview]
Message-ID: <037520b7-e17d-b516-a2da-a41ee8a1624a@redhat.com> (raw)
In-Reply-To: <87imgh5o82.fsf@linaro.org>

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?

 Thomas