Messages in this thread | | | Date | Mon, 13 May 2024 07:06:19 -0700 | From | Boqun Feng <> | Subject | Re: [PATCH 2/2] rust: time: Use wrapping_sub() for Ktime::sub() |
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On Thu, May 09, 2024 at 02:14:16PM +0200, Thomas Gleixner wrote: > On Tue, Apr 23 2024 at 14:11, Boqun Feng wrote: > > On Thu, Apr 11, 2024 at 04:08:01PM -0700, Boqun Feng wrote: > >> Currently since Rust code is compiled with "-Coverflow-checks=y", so a > >> normal substraction may be compiled as an overflow checking and panic > >> if overflow happens: > >> > >> subq %rsi, %rdi > >> jo .LBB0_2 > >> movq %rdi, %rax > >> retq > >> .LBB0_2: > >> pushq %rax > >> leaq str.0(%rip), %rdi > >> leaq .L__unnamed_1(%rip), %rdx > >> movl $33, %esi > >> callq *core::panicking::panic::h59297120e85ea178@GOTPCREL(%rip) > >> > >> although overflow detection is nice to have, however this makes > >> `Ktime::sub()` behave differently than `ktime_sub()`, moreover it's not > >> clear that the overflow checking is helpful, since for example, the > >> current binder usage[1] doesn't have the checking. > > > > Ping. Thomas, John and Stepthen. Could you take a look at this, and the > > discussion between Miguel and me? The key question is the behavior when > > ktime_sub() hits a overflow, I think. Thanks! > > In principle ktime_sub() should not overflow for regular use cases. > > If the binder example overflows the substraction, then something is > seriously wrong. Though in that case as it's only for debug purposes > panicing would be totally counter productive. A warning might be > appropriate though. >
Thanks! Looks to me, a reasonable implementation would be calling `overflowing_sub`[1] and print a warning if overflow happens:
<in the implementation of Sub trait of Ktime>
let (ret, overflow) = self.inner.overflowing_sub(other.inner);
if overflow { pr_err!("Overflow on Ktime: {} - {}\n", self.inner, other.inner); }
return ret;
I will use this as a new version for more reviews.
[1]: https://doc.rust-lang.org/std/primitive.i64.html#method.overflowing_sub
Regards, Boqun
> Thanks, > > tglx > >
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