On 13 June 2016 at 23:38, Richard Henderson <r...@twiddle.net> wrote: > On 06/13/2016 03:28 PM, Peter Maydell wrote: >> glibc's syscall() takes the system parameter as an int and >> does a sign-extending move into x0 with an uxtw. >> safe_syscall() takes a long, so it's already 64 bits. > > > Well, uxtw is a zero-extending move. So...
Yeah 'sign-extending' was a thinko. But the point is that for syscall() the input is 32 bits and the value it feeds to the kernel is 64 bits, hence the extension. For safe_syscall() the input is 64 bits and the value fed to the kernel is also 64 bits, so the most 'natural' thing is just to move a 64 bit value (saves the reader looking up whether mov wX, wY clears the high half or not, if nothing else). thanks -- PMM
