Messages in this thread |  | | Date | Mon, 20 Nov 2017 12:22:35 +0000 | From | Mark Rutland <> | Subject | Re: [RFC PATCH 1/2] arm64: write __range_ok() in C |
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On Thu, Nov 16, 2017 at 03:28:19PM +0000, Will Deacon wrote: > On Thu, Oct 26, 2017 at 10:09:41AM +0100, Mark Rutland wrote: > > +static bool __range_ok_c(unsigned long addr, unsigned long size) > > +{ > > + unsigned long result; > > + > > + if (__builtin_uaddl_overflow(addr, size, &result)) > > I'm not sure if you're planning to revisit this series, but thought I'd > give you a heads up that apparently GCC 4.x doesn't have support for this > builtin, so we'll need to carry the asm at least for that toolchain.
Thanks for the heads-up. I see my Linaro 14.09 GCC 4.9 generates an out-of-line call to a __builtin_uaddl_overflow helper.
We can avoid the builtin, and write the test in C instead, e.g.
static inline bool __range_ok_c(unsigned long addr, unsigned long size) { unsigned long end = addr + size;
if (end < addr) return false;
return end <= current_thread_info()->addr_limit; }
... in my standalone test-case, that generates code that's almost identical to the builtin, except that the compiler chooses to look at a different flag.
Thanks, Mark.
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