On Tuesday 02 June 2009 20:17:48 matthieu castet wrote: > Hi Michael, > > Michael Buesch wrote: > > On Tuesday 02 June 2009 00:00:12 matthieu castet wrote: > >> matthieu castet wrote: > >>> Hi, > >>> > >>> b43_generate_plcp_hdr generate unaligned access on mips with gcc [1] > >>> from openwrt. > >>> > >>> A small testcase [2] show that &plcp->data is access as a 32 bit aligned > >>> variable (see the "lw $2,0($4)" and "sw $2,0($4)"). > >>> I don't know enough mips to know if it is a gcc bug (ignoring the packed > >>> attribute) or something missing in b43 code. > >> For example using "plcp->data" instead "*data" produce the correct code. > > > > Uhm, I'm not sure. This code has been in the driver as-is forever and I don't > > see any unaligned access issues on mips (I checked a month or so ago). > Where does this pointer come from ? May be other code change change this > pointer alignement? > Which toolchain did you use ? > Could you try to build the testcase I posted and see which code it > generate ? OpenWRT trunk. > > The plcp data structure is also __attribute__((packed)), so there can't be any > > unaligned accesses, as gcc is required to _expect_ unaligned accesses on structures > > with packed attribute. So it is required to do byte accesses on architectures where > > alignment matters. > > So I don't think there's an issue in the code. > > > But the code doesn't use the structure to access the data. > It use by an extra pointer "data", and I believe gcc loose the packed > info (use byte accesses) when we do the "u32 *data = &plcp->data". Ok, yeah. Maybe they changed semantics then. Can you send a patch please? I do actually prefer patches anyway instead of verbose explanations. I'd have immediately understood what you were talking about, if you'd just sent a patch. ;) -- Greetings, Michael. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
