On Thu, May 18, 2017 at 1:19 PM, Laszlo Ersek <[email protected]> wrote: > On 05/16/17 14:10, Sergei Temerkhanov wrote: >> On Tue, May 16, 2017 at 8:10 AM, Gao, Liming <[email protected]> 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. > 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:[email protected]] On Behalf Of >>>> Sergey Temerkhanov >>>> Sent: Tuesday, May 16, 2017 10:57 AM >>>> To: [email protected] >>>> Subject: [edk2] [PATCH] MdePkg: Fix undefined behavior on variadic >>>> parameters >>>> >>>> Fix undefined behavior by avoiding parameter type promotion >>>> >>>> Signed-off-by: Sergey Temerkhanov <[email protected]> >>>> --- >>>> 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 >>>> [email protected] >>>> https://lists.01.org/mailman/listinfo/edk2-devel >> _______________________________________________ >> edk2-devel mailing list >> [email protected] >> https://lists.01.org/mailman/listinfo/edk2-devel >> > _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
