Messages in this thread | | | From | Arnd Bergmann <> | 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 | Date | Wed, 01 Oct 2014 16:00:54 +0200 |
| |
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.
> 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.
Arnd
| |