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

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

On Wed, May 24, 2017 at 5:46 AM, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
> Sergey,
>
> We also need to do a full search for use of variadic parameters to make
> sure we have a solution for all of them and update the EDK II C coding
> standard to make sure the rules for use of variadic parameters for
> maximum compiler compatibility are captured correctly.

I've sent another patch for MdePkg with a similar change but there
might be more.

>
> Did you try Andrew Fish's suggestion to add -Wno-varargs to the components
> that have this issue to see if that is a temporary workaround for your
> specific build failures?

For my projects, using these 2 changes have been sufficient .

>
> Thanks,
>
> Mike
>
>> -----Original Message-----
>> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Gao, Liming
>> Sent: Tuesday, May 23, 2017 7:14 PM
>> To: 'Laszlo Ersek' <lersek@redhat.com>; Sergei Temerkhanov <s.temerkhanov@gmail.com>
>> Cc: edk2-devel@lists.01.org
>> Subject: Re: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic parameters
>>
>> Sergey:
>>   This patch updates API interface. I still need to verify its functionality on other
>> tool chain. I will give you feedback after I am done.
>>
>> Thanks
>> Liming
>> >-----Original Message-----
>> >From: Laszlo Ersek [mailto:lersek@redhat.com]
>> >Sent: Friday, May 19, 2017 4:16 PM
>> >To: Sergei Temerkhanov <s.temerkhanov@gmail.com>
>> >Cc: Gao, Liming <liming.gao@intel.com>; edk2-devel@lists.01.org
>> >Subject: Re: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic
>> >parameters
>> >
>> >On 05/19/17 04:45, Sergei Temerkhanov wrote:
>> >> On Thu, May 18, 2017 at 1:19 PM, Laszlo Ersek <lersek@redhat.com> wrote:
>> >>> 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.
>> >>
>> >> On 32-bit architectures, using 64-bit types here may change the ABI. Which
>> >might
>> >> affect some corner cases like linking precompiled object files to the
>> >> library in question.
>> >
>> >True.
>> >
>> >I missed the fact that in edk2 you can have binary-only library
>> >instances. I should have remembered, after all I had filed
>> ><https://bugzilla.tianocore.org/show_bug.cgi?id=463> :)
>> >
>> >So yes, UINTN is the best choice; it keeps binary compat beyond
>> >everything else.
>> >
>> >Thanks!
>> >Laszlo
>> >
>> >>
>> >>> 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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>> >>>>>> https://lists.01.org/mailman/listinfo/edk2-devel
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>> >>>>
>> >>>
>>
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