Messages in this thread | | | Date | Sat, 27 Feb 2016 23:53:56 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread |
| |
----- On Feb 27, 2016, at 1:35 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Sat, Feb 27, 2016 at 6:58 AM, Peter Zijlstra <peterz@infradead.org> wrote: >> >> Paul's patches have the following structure: >> >> struct thread_local_abi { >> union { >> struct { >> u32 cpu_id; >> u32 seq; >> }; >> u64 cpu_seq; >> }; >> unsigned long post_commit_ip; >> }; > > Please don't do "unsigned long" in ABI structures any more. > > Make it u64, and make sure it is 64-bit aligned (which it would be in > this case). Make it so that we don't have to have separate compat > paths.
AFAIU, this "post_commit_ip" field is expected to be updated with a single-copy-store by user-space. If we want to handle both 32-bit and 64-bit processes, how do you recommend doing this without an unsigned long type ?
A 64-bit integer would not be a single-copy store for 32-bit processes, but a 32-bit integer would not be large enough for 64-bit processes.
Would a
union { uint32_t val32; uint64_t val64; } field;
be an acceptable option ? Then the kernel could use one field or the other depending on the process bitness.
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
| |