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Re: [PATCH] Allocate extra 16 bytes for -fsanitize=address


On Fri, Nov 23, 2012 at 10:08:11AM -0800, H.J. Lu wrote:
> > to also change the caller, read_file_guts, where it does
> >   buf = XNEWVEC (uchar, size + 1);
> > and
> >           buf = XRESIZEVEC (uchar, buf, size + 1);
> 
> I don't think it is necessary since there is no real data in
> those extra 16 bytes.  They can have garbage and libcpp still
> functions correctly.  They are purely used to silence ASAN.

The thing is, if the buf from the caller has such size/total
combination that if (to.len + 4096 < to.asize || to.len >= to.asize)
isn't true, there won't be any reallocation and the buffer passed
in from the caller will be used instead.  And, if it doesn't have those
extra 16 bytes, it will still result in asan warning...
Guess you need to read file from stdin instead of a file for that
to trigger that.

For valgrind I bet just clearing those 16 bytes might still be cheap enough
not to worry about it.

> > I'll defer the review to Tom though.
> >
> >> 2012-11-21  H.J. Lu  <hongjiu.lu@intel.com>
> >>
> >>       PR bootstrap/55380
> >>       * charset.c (_cpp_convert_input): Allocate extra 16 bytes for
> >>       -fsanitize=address if __SANITIZE_ADDRESS__ is defined.
> >>
> >> diff --git a/libcpp/charset.c b/libcpp/charset.c
> >> index cba19a6..dea8bb1 100644
> >> --- a/libcpp/charset.c
> >> +++ b/libcpp/charset.c
> >> @@ -1729,9 +1729,16 @@ _cpp_convert_input (cpp_reader *pfile, const char *input_charset,
> >>      iconv_close (input_cset.cd);
> >>
> >>    /* Resize buffer if we allocated substantially too much, or if we
> >> -     haven't enough space for the \n-terminator.  */
> >> +     haven't enough space for the \n-terminator.  Allocate extra 16
> >> +     bytes for -fsanitize=address.  */
> >>    if (to.len + 4096 < to.asize || to.len >= to.asize)
> >> -    to.text = XRESIZEVEC (uchar, to.text, to.len + 1);
> >> +    {
> >> +#ifdef __SANITIZE_ADDRESS__
> >> +      to.text = XRESIZEVEC (uchar, to.text, to.len + 17);
> >> +#else
> >> +      to.text = XRESIZEVEC (uchar, to.text, to.len + 1);
> >> +#endif
> >> +    }
> >>
> >>    /* If the file is using old-school Mac line endings (\r only),
> >>       terminate with another \r, not an \n, so that we do not mistake

	Jakub


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