On Thu, Dec 01, 2011 at 04:44:40PM +0000, Arnd Bergmann wrote:
On Thursday 01 December 2011, Catalin Marinas wrote:
On Thu, Dec 01, 2011 at 03:42:19PM +0000, Arnd Bergmann wrote:
On Thursday 01 December 2011, Catalin Marinas wrote: 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).
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What about unsigned long and pointer? Can we always rely on the upper half of the register to be zero-filled when we get an exception from 32 bit into 64 bit state, or do we also have to zero-extend those?
They are also fine, no need for zero-extension.