Re: [Qemu-devel] [PATCH] support >2TB SCSI disks

["M. Warner Losh" <imp@bsdimp.com>]

In message: <200901281230.29455.paul@codesourcery.com>
            Paul Brook <paul@codesourcery.com> writes:
: >      case 0:
: > -        lba = buf[3] | (buf[2] << 8) | ((buf[1] & 0x1f) << 16);
: > +        lba = (uint64_t) buf[3] | ((uint64_t) buf[2] << 8) |
: > +              (((uint64_t) buf[1] & 0x1f) << 16);
: 
: This is not required, though I guess it's harmless.

Actually, I think it is required.  ANSI-C promotion rules say that a
char or unsigned char is promoted to an int when used in an
expression.  This causes the result to be a 32-bit number which is
sign-extended to a 64-bit number before being assigned to lba.

I've hit this "bug" in C before many times, and the patch specifically
called it out as a problem.

Warner