Messages in this thread | | | Date | Thu, 2 Oct 2014 12:19:51 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH 08/24] Allow a 32bit ABI to use the naming of the 64bit ABI syscalls to avoid confusion of not splitting the registers |
| |
On Wed, Oct 01, 2014 at 03:00:54PM +0100, Arnd Bergmann wrote: > On Wednesday 01 October 2014 13:42:27 Catalin Marinas wrote: > > On Thu, Sep 04, 2014 at 11:11:04AM +0100, Arnd Bergmann wrote: > > > On Wednesday 03 September 2014 14:19:02 Andrew Pinski wrote: > > > > + * For 32bit abis where 64bit can be passed via one > > > > + * register, use the same naming as the 64bit ones > > > > + * as they will only have a 64 bit off_t. > > > > */ > > > > -#if __BITS_PER_LONG == 64 && !defined(__SYSCALL_COMPAT) > > > > +#if (__BITS_PER_LONG == 64 && !defined(__SYSCALL_COMPAT)) || \ > > > > + defined(__ARCH_WANT_64BIT_SYSCALLS) > > > > > > I'm not sure if __ARCH_WANT_64BIT_SYSCALLS is the best name for > > > this, since it's really only about off_t. It took me a while > > > to understand what you are doing here. > > > > I'm not sure I fully get it yet. So with this change, we avoid using > > syscall numbers like __NR_ftruncate64 in favour of __NR_ftruncate. Why? > > (maybe there's a valid reason, just not getting it). > > glibc depends on the name to decide which calling conventions it > uses. I assume this is the same on IPL32 ARM. > > The general rule is that on a 32-bit architecture, __NR_ftruncate refers > to the system call that takes a 32-bit off_t argument, while __NR_ftruncate64 > refers to the syscall that takes a 64-bit loff_t. > > I would assume that the new ABI does not actually allow using 32-bit off_t > in applications (that would be silly) and defaults to using 64-bit offsets, > but it still needs to generate the right system calls.
OK, so since ILP32 would have a 64-bit off_t, we want to use __NR_ftruncate and sys_ftruncate with the off_t argument (rather than loff_t).
> > Either way, ILP32 would still end up calling sys_ftruncate64() (rather > > than the native sys_ftruncate()). > > sys_ftruncate64 does not exist in 64-bit kernels, it can either call > compat_sys_ftruncate64_wrapper or sys_ftruncate. I'd assume it would > call the latter and pass a single 64-bit register, but that is another > matter.
I think I get it now. Just for the record, we define __NR_ftruncate to __NR3264_ftruncate. When we build the syscall table as per patch 21/24, given that the kernel is built with __LP64__, we get the following macros for the syscall function name:
#define __SC_3264(_nr, _32, _64) __SYSCALL(_nr, _64) #define __SC_COMP_3264(_nr, _32, _64, _comp) __SC_3264(_nr, _32, _64) ... __SC_COMP_3264(__NR3264_ftruncate, sys_ftruncate64, sys_ftruncate, \ compat_sys_ftruncate64)
Which would result in using sys_ftruncate rather than sys_ftruncate64.
I agree, maybe the name could be __ARCH_WANT_64BIT_OFF_T as that's the only reason for these definitions.
-- Catalin
| |