Hi, On 17/01/18 15:42, Jaromír Mikeš wrote: > Hi, > > giada unfortunately fail to build on some archs ... I already informed > upstream but not answer yet. > Can someone look if fixing this is rather trivial or complicated. > > https://buildd.debian.org/status/package.php?p=giada
The entire function for reference:
> std::string gu_format(const char* format, ...)
> {
> va_list args;
>
> /* Compute the size of the new expanded string (i.e. with replacement
> taken
> into account). */
>
> size_t size = vsnprintf(nullptr, 0, format, args);
>
> /* Create a new temporary char array to hold the new expanded string. */
>
> std::unique_ptr<char[]> tmp(new char[size]);
>
> /* Fill the temporary string with the formatted data. */
>
> va_start(args, format);
> vsprintf(tmp.get(), format, args);
> va_end(args);
>
> return string(tmp.get(), tmp.get() + size - 1);
> }
This line (the one the error complains about) reads the uninitialized
args and invokes undefined behavior:
> size_t size = vsnprintf(nullptr, 0, format, args);
It needs to be surrounded in va_start, va_end block.
The second subtle error is that vsnprintf returns the size _excluding
the null byte_. This will cause the vsprintf call to overflow the buffer
by 1 byte.
This might work (untested):
va_start(args, format);
size_t size = vsnprintf(nullptr, 0, format, args) + 1;
va_end(args);
Some alternative implementations. The varardic template solution (the
third one) is similar to this code (and the one I like the most):
https://stackoverflow.com/questions/2342162/stdstring-formatting-like-sprintf
James
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