David Miller <davem@xxxxxxxxxxxxx> writes: > From: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> > Date: Wed, 2 Feb 2011 16:37:02 +0000 > >> 1. there's no way to tell GCC that the inline assembly is a load >> instruction and therefore it needs to schedule the following >> instructions appropriately. > > Just add a dummy '"m" (pointer)' asm input argument to the inline asm > statement. Just make sure "typeof(pointer)" has a size matching the > size of the load your are performing. That should be "m"(*pointer). >> 2. GCC will needlessly reload pointers from structures and other such >> behaviour because it can't be told clearly what the inline assembly >> is doing, so the inline asm needs to have a "memory" clobber. > > This behavior is correct, and in fact needed. Writing to chip registers > can trigger changes to arbitrary main memory locations. > >> 3. It seems to misses out using the pre-index addressing, prefering to >> create add/sub instructions prior to each inline assembly load/store. > > Yes, this is indeed a problem. GCC has trouble doing anything more complicated than simple indexing. Load/store instructions with writeback seem not to be in its vocabulary at all. > But you really need that memory clobber there whether you like it or > not, see above. I don't know of any device where the side-effects are not explicitly indicated by other means in the code triggering them, so it probably is safe without the clobber as Russel says. -- Måns Rullgård mans@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
