On Mon, Oct 14, 2013 at 11:57:29PM +0800, Jiang Liu wrote: > On 10/14/2013 11:40 PM, Russell King - ARM Linux wrote: > > On Sun, Oct 13, 2013 at 10:50:20PM +0800, Jiang Liu wrote: > >> To enable this feature, your toolchain must support "asm goto" extension > >> and "%c" constraint extesion. Current GCC for AARCH64 doesn't support > >> "%c", so you need a GCC patch similiar to this: > > > > Oh god, not that again. I've no idea why ARM stuff has such a problem with > > supporting this very useful "%c" GCC constraint. Aarch32 didn't for ages > > consequently we now have horrid hacks around it in the kernel source > > because our compilers suck. Seems Aarch64 is doomed to repeat the same > > stupid mistakes. :( > > > We need to do the same trick for ARM64 too:)
Just been locating it - it's part of the gcc internals documentation: | In the simplest case, a `%' followed by a digit N says to output | operand N at that point in the string. | | `%' followed by a letter and a digit says to output an operand in an | alternate fashion. Four letters have standard, built-in meanings | described below. The machine description macro `PRINT_OPERAND' can | define additional letters with nonstandard meanings. | | `%cDIGIT' can be used to substitute an operand that is a constant | value without the syntax that normally indicates an immediate operand. | ... | `%lDIGIT' is used to substitute a `label_ref' into a jump instruction. %lDIGIT is used (but not commented upon) in the gcc extended asm documentation where it talks about asm gotos, so there's probably a doc bug here too about whether these options should be described in the main doc as well. Nevertheness, this section is documenting the _internals_ of gcc, and it seems perverse for a gcc backend to ignore something that is documented as being a standard part of gcc. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
