[PATCH] vfwprintf.c

[Jeff Johnston]

Yufeng,

I'm having trouble verifying this patch.  I think there may possibly be 
another issue in newlib.  When I apply the patch and build both an 
x86-linux version of newlib and mn10300 version of newlib, neither pass 
the test.  They are both padding the result with zeroes.

Even weirder is that if I change the test to use sprintf, mn10300 gives 
the expected result whereas x86-linux is not.

I need to look at this a bit more.  It is currently Eclipse release 
train time so I haven't had a long time to look at why my results vary.

Were you able to verify this worked and what platform did you 
configure/test on?

-- Jeff J.

On 06/09/2011 08:50 AM, Yufeng Zhang wrote:
> Hi,
>
> This patch fixes a problem in the newlib vfwprintf implementation.
>
> For each conversion specifier in the format string that is [feEgG], the
> current vfwprintf implementation provides only a 40-length wide-char
> buffer for conversion. This causes code like the following to misbehave.
>
>    wchar_t largebuf[512];
>    double val = 1.7976931348623158e+308;
>    swprintf(largebuf, 512, L"%.*f", 3, val);
>
> Only the first 40 characters can be correctly converted due to the
> limited length of the buffer. This will cause junk in the rest of the
> converted wide-char sequence, and can potentially corrupt the memory
> immediately after 'largebuf'.
>
> The example code is a repro of the libstdc++-v3 test
> ./libstdc++-v3/testsuite/27_io/basic_ostream/inserters_arithmetic/wchar_t/44
> 02.cc
> which currently fails when newlib is used as the C library.
>
> The patch was prepared with the consideration of minimum code change.
> It is probably not worth a bigger surgery in the code since the
> conversion of extremely long wide char sequence is fairly rare.
>
> The 2nd attached patch adds a test to the testsuite.
>
> Thanks,
> Yufeng
>
>
> newlib/ChangeLog
> 2011-06-09  Yufeng Zhang<yufeng.zhang@arm.com>
>
>          * libc/stdio/vfwprintf.c (wcvt): Add new parameter 'len' of type
>          int.  Replace BUF with len.
>          (VFWPRINTF): Add extra call to wcvt with a malloced new buffer,
>          when the fixed-length buffer 'buf' is not large enough.