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

["Kinney, Michael D" <michael.d.kinney@intel.com>]

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.

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?

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
> >>>>>>
> >>>>>> _______________________________________________
> >>>>>> edk2-devel mailing list
> >>>>>> edk2-devel@lists.01.org
> >>>>>> https://lists.01.org/mailman/listinfo/edk2-devel
> >>>> _______________________________________________
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> >>>> edk2-devel@lists.01.org
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> >>>>
> >>>
> 
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