On Thu, Dec 01, 2011 at 03:42:19PM +0000, Arnd Bergmann wrote: > On Thursday 01 December 2011, Catalin Marinas wrote: > > Given the way register banking is done on AArch64, issuing an HVC on a > > 32-bit guest OS doesn't require translation on a 64-bit hypervisor. We > > have a similar implementation at the SVC level (for 32-bit user apps on > > a 64-bit kernel), the only modification was where a 32-bit SVC takes a > > 64-bit parameter in two separate 32-bit registers, so packing needs to > > be done in a syscall wrapper. > > How do you deal with signed integer arguments passed into SVC or HVC from > a caller? If I understand the architecture correctly, the upper > halves of the argument register end up zero-padded, while the callee > expects sign-extension.
If you treat it as an "int" (32-bit) and function prototype defined accordingly, then the generated code only accesses it as a W (rather than X) register and the top 32-bit part is ignored (no need for sign-extension). If it is defined as a "long" in the 32-bit world, then it indeed needs explicit conversion given the different sizes for long (for example sys_lseek, the second argument is a 'long' and we do explicit sign extension in the wrapper). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
