[cfe-dev] printf: invalid conversion specifier: 'I' when using "I64d" on Windows

[Ruben Van Boxem]

2012/8/8 Jordan Rose <jordan_rose at apple.com>

> Interesting. Shouldn't be too hard to add support here (conditioned on
> -fms-compatibility, perhaps?), and PrintfFormatString is probably the right
> place to do this. If you don't feel comfortable writing a patch yourself,
> please file a bug at http://llvm.org/bugs/ and eventually someone will
> get to it. (Perhaps Hans, since he's been doing a number of format string
> fixes lately?)
>

If -fms-compatibility is enabled by default on Windows, this is fine by me.
But I noticed the glibc and objc stuff is just "in plain sight" too, is
this intended or just "easier to implement"?

I can take a look tomorrow and based on my findings/trials I'll submit a
bug report and/or patch ;-) Unless someone beats me to it of course...

Ruben


>
> Thanks for catching this!
> Jordan
>
>
> On Aug 8, 2012, at 13:48 , Ruben Van Boxem <vanboxem.ruben at gmail.com>
> wrote:
>
> Hi,
>
> Windows' msvcrt.dll has weird printf format strings that aren't used
> anywhere else.
>
> For example this code with Clang 3.1 on MinGW-w64 using GCC 4.6.3
> libstdc++ headers:
> #define __STDC_FORMAT_MACROS
> #include <inttypes.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <stdint.h>
> #include <fstream>
> int main(int argc,char **argv)
> {
>    uint64_t val=1234567890;
>    printf("%" PRId64"\n",val);
>    exit(0);
> }
>
> produces this warning:
> M:\Development\x64\test>clang++ -std=c++11 test.cpp -c -Wall
> test.cpp:11:15: warning: invalid conversion specifier 'I'
>       [-Wformat-invalid-specifier]
>    printf("%" PRId64"\n",val);
>            ~~~^
> M:/Development/mingw64/bin/../lib/clang/3.1/../../../x86_64-w64-mingw32/include\inttypes.h:42:17:
> note:
>       expanded from macro 'PRId64'
> #define PRId64 "I64d"
>                 ^
> 1 warning generated.
>
> The "I64d" form is the "correct" msvcrt printf format string for this
> case, and the define in the mingw-w64 header inttypes.h is used to make the
> code correct and thus work around the msvcrt limitations.
>
> Clang (and don't worry, GCC too) warns on this use, while it really
> shouldn't, as this is correct on Windows. I understand from a MinGW-w64 dev
> that they annotate their printf prototype correctly, but the compiler's
> builtin definition conflicts with this, and hence the warning. So I think
> the right solution here is to allow the MS printf format strings as well.
> This should work for both Visual Studio based and MinGW-w64 based Clang.
>
> I was looking through the code, and found:
>
> http://llvm.org/svn/llvm-project/cfe/trunk/lib/Analysis/PrintfFormatString.cpp
> where I think the format string is handled, because printf is defined in
> http://llvm.org/svn/llvm-project/cfe/trunk/include/clang/Basic/Builtins.def
> as a builtin.
> The warning is thrown from
> http://llvm.org/svn/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp
> as "diag::warn_format_invalid_conversion" I *think*.
>
> Am I right that there should be a modification to PrintfFormatString.cpp
> (and maybe ScanfFormatString.cpp as well?) to allow the MS specific format
> specifiers as defined here
> http://msdn.microsoft.com/en-us/library/56e442dc.aspx ?
>
> I would prepare a patch, but I have no idea if the above is correct and
> what exactly (and how) I'd have to add this.
>
> Therefore: any help is much appreciated!
>
> Thanks,
>
> Ruben
>
> PS: please reply to my email directly as well, I'm not subscribed to
> cfe-dev
>
>
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>
>
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