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

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

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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