[R-pkg-devel] truncating strings on purpose

[Brad Eck]

Hi Ivan, List,

Thanks for the suggestion, and for the pointer on duplicating the error.
The good news is that I am able to trigger the warning locally now. The bad
news is that following the gcc docs on avoid the warning did not seem to
work:


gcc -std=gnu99 -fsanitize=undefined -fno-omit-frame-pointer -std=gnu11
-I"/usr/local/lib/R/include" -DNDEBUG   -I/usr/local/include
-fsanitize=address
-O2 -Wstringop-truncation -fPIC  -g -O2  -c input2.c -o input2.o

input2.c: In function ‘inperrmsg’:

input2.c:863:5: warning: ‘strncpy’ output may be truncated copying 225
bytes from a string of length 255 [-Wstringop-truncation]

  863 |     strncpy(trunc_tok, tok, sizeof trunc_tok - 1);

      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




I could also try memcpy, but i don't so much like the idea of going away
from string functions for string handling.


Other suggestions are also welcome.


Brad



On Wed, Dec 11, 2024 at 1:29 PM Ivan Krylov <ikrylov using disroot.org> wrote:

> В Wed, 11 Dec 2024 12:12:11 +0000
> Brad Eck <bradleyjeck using gmail.com> пишет:
>
> > Found the following significant warnings:
> >     input2.c:863:5: warning: ‘__builtin_strncpy’ output may be
> > truncated copying 225 bytes from a string of length 255
> > [-Wstringop-truncation]
>
> > Where the truncation warnings appear, I am truncating on purpose
> > using `strncpy` to avoid overflows later.  I believe this works fine
> > from an application point of view but the warnings remain.
>
> GCC documentation suggests setting the length argument to _one less_
> than sizeof destination buffer in addition to terminating the string:
>
> https://gcc.gnu.org/onlinedocs/gcc-14.2.0/gcc/Warning-Options.html#index-Wstringop-truncation
>
>         strncpy(trunc_s1, s1, sizeof trunc_s1 - 1);
>         trunc_s1[sizeof trunc_s1 - 1] = '\0';
>
> --
> Best regards,
> Ivan
>

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