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

["Gao, Liming" <liming.gao@intel.com>]

Laszlo:
  Based on your analysis, the parameter type should be changed from BOOLEAN to INT32 to match its promotion type. Right?

Thanks
Liming
>-----Original Message-----
>From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
>Laszlo Ersek
>Sent: Thursday, May 18, 2017 6:20 PM
>To: Sergei Temerkhanov <s.temerkhanov@gmail.com>; Gao, Liming
><liming.gao@intel.com>
>Cc: edk2-devel@lists.01.org
>Subject: Re: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic
>parameters
>
>On 05/16/17 14:10, Sergei Temerkhanov wrote:
>> 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
>
>Side topic:
>
>It is promoted, but not to "unsigned int".
>
>The standard says, in "6.3.1.1 Boolean, characters, and integers",
>paragraph 2,
>
>    The following may be used in an expression wherever an /int/ or
>    /unsigned int/ may be used:
>
>    — An object or expression with an integer type whose integer
>      conversion rank is less than or equal to the rank of /int/ and
>      /unsigned int/.
>    — A bit-field of type /_Bool/, /int/, /signed int/, or
>      /unsigned int/.
>
>    If an /int/ can represent all values of the original type, the value
>    is converted to an /int/; otherwise, it is converted to an
>    /unsigned int/. These are called the /integer promotions/. [...]
>
>On all supported edk2 platforms, "unsigned char"'s range is 0..255
>inclusive, which can be represented by "int" (again on all supported
>edk2 platforms). So the promotion occurs to "int", not "unsigned int"
>
>
>Furthermore, in place of the suggested UINTN type (which is fine), the
>following further types would be correct: INT32, UINT32, INT64, UINT64,
>INTN. The reason is that all of these map to standard C types, on all
>edk2 platforms, whose integer conversion ranks are not less than that of
>"int" and "unsigned int". Hence they are all unaffected by the integer
>promotions.
>
>(This digression does not affect your main point, which remains correct;
>I just wanted to be precise here, since we're quoting the standard.)
>
>Thanks
>Laszlo
>
>> 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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