On Tue, 2006-12-19 at 18:30 +0200, Momchil Velikov wrote: > Ming Zhang wrote: > > On Tue, 2006-12-19 at 18:00 +0200, Momchil Velikov wrote: > >> Ming Zhang wrote: > >>> On Tue, 2006-12-19 at 12:56 +0200, Momchil Velikov wrote: > >>>> Arjan van de Ven wrote: > >>>>> On Mon, 2006-12-18 at 17:12 -0500, Ming Zhang wrote: > >>>>>> See this code piece > >>>>>> > >>>>>> http://lxr.linux.no/source/drivers/scsi/libata-scsi.c?v=2.6.18#L1049 > >>>>>> > >>>>>> 1056 lba |= ((u64)scsicmd[2]) << 24; > >>>>>> 1057 lba |= ((u64)scsicmd[3]) << 16; > >>>>>> 1058 lba |= ((u64)scsicmd[4]) << 8; > >>>>>> 1059 lba |= ((u64)scsicmd[5]); > >>>>>> > >>>>>> it can also be written as > >>>>>> > >>>>>> lba = be32_to_cpu(*(u32 *)(&scsicmd[2]) > >>>> ISO/IEC 9899:1999(E) "6.5 Expressions" [#7] > >>> read but still can not understand why u list this here. > >> Because this code > >> > >> ba = be32_to_cpu(*(u32 *)(&scsicmd[2]) > >> > >> violates this requirement > >> > >> ISO/IEC 9899:1999(E) "6.5 Expressions" [#7] > >> > >> unless you have checked in all callers of ``scsi_10_lba_len'' (and > >> transitively in their callers, if necessary) that the first parameter in > >> fact does refer to an object of type ``u32'', in which case the above > >> code becomes simply non-robust instead of outright non-conforming. > >> > > > > scsicmd is u8*, so scsicmd + 2 is also u8*, why can not cast it to u32*? > > u* is a unsigned char so a character type" right? > > Who said you cannot cast it? The referred to text in the standard > speaks about *access* to object's stored value, not casts. so although the code can cast, the original value in that memory area is a series of u8. not u32. so this is the problem? > > ~velco -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
