> On 18 Dec 2015, at 13:47, Arnd Bergmann <a...@arndb.de> wrote: > >> 3. Follow the PCS up to glibc but always pass syscall arguments in W >> registers, like AArch32 compat support (the least preferred option, >> the only advantage is a single wrapper for all syscalls but it would >> be doing unnecessary zeroing even for syscalls where it isn't needed) > > This would mean we cannot pass 64-bit arguments in registers, right?
Note that there’s no 32bit registers (the ‘w’-form always refers to the lower 32bits of a 64bit register, with implicit zero-extension)… and load/store instructions always use the full base-register (‘x’-form) for address calculation. I.e. a load/store would inadvertently pickup “random garbage” in the upper 32bits, if no explicit zero-extension is applied. In other words: all zero-extensions for 32bit arguments should be explicit on the kernel side. Regards, Philipp. -- 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/