Re: [PATCH] MdePkg: Fix undefined behavior on variadic parameters

[Sergei Temerkhanov <s.temerkhanov@gmail.com>]

On Thu, May 18, 2017 at 6:06 AM, Andrew Fish <afish@apple.com> wrote:
> Sergei,
>
> We are hitting this too.
>
> Our temporary work around was to suppress the warning for the libraries via our platforms DSC file so we did not need to override things in edk2.
>
> You can override the library build options if you add them to the [Components] section.
>
> MdePkg/Library/UefiLib/UefiLib.inf {
>   <BuildOptions>
>     XCODE:*_*_*_CC_FLAGS  = -Wno-varargs

That would be GCC: *_CLANG38_*_CC_FLAGS at least

> }
>
> Thanks,
>
> Andrew Fish
>
>> On May 17, 2017, at 5:26 PM, Sergei Temerkhanov <s.temerkhanov@gmail.com> wrote:
>>
>> On Wed, May 17, 2017 at 6:30 PM, Gao, Liming <liming.gao@intel.com> wrote:
>>> Sergey:
>>>  Now, VS and GCC don't report such issue. How do you find them?
>>
>> Clang build for ARM64 revealed it.
>>
>>> And, this change modifies the function API, does it impact the consumer code?
>>
>> No changes to the consumer code are needed - integer promotions are
>> handled by the compilers. In fact, even the ABI remains the same b/c
>> full words are passed as function parameters.
>>
>> Regards,
>> Sergey
>>
>>>
>>> Thanks
>>> Liming
>>>> -----Original Message-----
>>>> From: Sergei Temerkhanov [mailto:s.temerkhanov@gmail.com]
>>>> Sent: Tuesday, May 16, 2017 8:11 PM
>>>> To: Gao, Liming <liming.gao@intel.com>
>>>> Cc: edk2-devel@lists.01.org
>>>> Subject: Re: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic parameters
>>>>
>>>> On Tue, May 16, 2017 at 8:10 AM, Gao, Liming <liming.gao@intel.com> wrote:
>>>>> Sergey:
>>>>>  Could you give more detail on the undefined behavior on variadic parameters?
>>>>>
>>>>>  I see https://bugzilla.tianocore.org/show_bug.cgi?id=410 describe this issues found in the latest CLANG tool chain. Do you find
>>>> other tool chain reports it?
>>>>
>>>> Yes, this is exactly the bug this patch fixes.
>>>>
>>>> As per the C99 standard:
>>>> "The parameter parmN is the identifier of the rightmost parameter in
>>>> the variable parameter list in the function definition (the one just
>>>> before the , ...). If the parameter parmN is declared with the
>>>> register storage class, with a function or array type, or with a type
>>>> that is not compatible with the type that results after application of
>>>> the default argument promotions, the behavior is undefined."
>>>>
>>>> That's exactly the case here since BOOLEAN is a typedef for unsigned
>>>> char. It undergoes a promotion to an unsigned int which is not a
>>>> compatible type for unsigned char. Correct me if I'm wrong.
>>>>
>>>> Regards,
>>>> Sergey
>>>>
>>>>>
>>>>> Thanks
>>>>> Liming
>>>>>> -----Original Message-----
>>>>>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Sergey Temerkhanov
>>>>>> Sent: Tuesday, May 16, 2017 10:57 AM
>>>>>> To: edk2-devel@lists.01.org
>>>>>> Subject: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic parameters
>>>>>>
>>>>>> Fix undefined behavior by avoiding parameter type promotion
>>>>>>
>>>>>> Signed-off-by: Sergey Temerkhanov <s.temerkhanov@gmail.com>
>>>>>> ---
>>>>>> MdePkg/Include/Library/UefiLib.h | 2 +-
>>>>>> MdePkg/Library/UefiLib/UefiLib.c | 2 +-
>>>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/MdePkg/Include/Library/UefiLib.h b/MdePkg/Include/Library/UefiLib.h
>>>>>> index 0b14792..4e4697c 100644
>>>>>> --- a/MdePkg/Include/Library/UefiLib.h
>>>>>> +++ b/MdePkg/Include/Library/UefiLib.h
>>>>>> @@ -818,7 +818,7 @@ CHAR8 *
>>>>>> EFIAPI
>>>>>> GetBestLanguage (
>>>>>>   IN CONST CHAR8  *SupportedLanguages,
>>>>>> -  IN BOOLEAN      Iso639Language,
>>>>>> +  IN UINTN      Iso639Language,
>>>>>>   ...
>>>>>>   );
>>>>>>
>>>>>> diff --git a/MdePkg/Library/UefiLib/UefiLib.c b/MdePkg/Library/UefiLib/UefiLib.c
>>>>>> index a7eee01..74528ec 100644
>>>>>> --- a/MdePkg/Library/UefiLib/UefiLib.c
>>>>>> +++ b/MdePkg/Library/UefiLib/UefiLib.c
>>>>>> @@ -1514,7 +1514,7 @@ CHAR8 *
>>>>>> EFIAPI
>>>>>> GetBestLanguage (
>>>>>>   IN CONST CHAR8  *SupportedLanguages,
>>>>>> -  IN BOOLEAN      Iso639Language,
>>>>>> +  IN UINTN      Iso639Language,
>>>>>>   ...
>>>>>>   )
>>>>>> {
>>>>>> --
>>>>>> 2.7.4
>>>>>>
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