Re: [Qemu-devel] [5274] Add signed versions of save/load functions

[Anthony Liguori <anthony@codemonkey.ws>]

Blue Swirl wrote:
> -int qemu_get_byte(QEMUFile *f)
> +int8_t qemu_get_byte(QEMUFile *f)
>  {
>      if (f->buf_index >= f->buf_size) {
>          qemu_fill_buffer(f);
> @@ -6329,13 +6329,13 @@
>      return pos;
>  }
>   

So this is the problem.  While qemu_get_byte() returns an int, it 
returns f->buf[pos] and buf is a uint8_t *.  This means that it will 
always return a positive number whereas the new qemu_get_byte() may 
return a negative number.

When dealing with something like qemu_get_be32(), where you're shifting 
qemu_get_byte(), the int8_t is going to get promoted to an int and when 
the int8_t is negative, the result is that the combination is an OR of 
0xFFFFFFFX instead of 0x000000FX.

Which leads me to wonder, how much did you test this changeset?  Because 
I don't think any save/restore could possibly have worked.  Perhaps we 
should revert the whole patchset until it's a bit more flushed out?  I'm 
concerned that integer promotion isn't taken into account in a number of 
places.

Regards,

Anthony Liguori