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

["Alex Bennée" <alex.bennee@linaro.org>]

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.

-- 
Alex Bennée