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

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

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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