Date: Sun, 21 Aug 2016 13:52:07 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Ed Schouten <ed@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r304555 - head/sys/compat/cloudabi Message-ID: <20160821105207.GS22212@zxy.spb.ru> In-Reply-To: <201608210741.u7L7fBnN075023@repo.freebsd.org> References: <201608210741.u7L7fBnN075023@repo.freebsd.org>
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On Sun, Aug 21, 2016 at 07:41:11AM +0000, Ed Schouten wrote: > Author: ed > Date: Sun Aug 21 07:41:11 2016 > New Revision: 304555 > URL: https://svnweb.freebsd.org/changeset/base/304555 > > Log: > Use memcpy() to copy 64-bit timestamps into the syscall return values. > > On 32-bit platforms, our 64-bit timestamps need to be split up across > two registers. A simple assignment to td_retval[0] will cause the top 32 > bits to get lost. By using memcpy(), we will automatically either use 1 > or 2 registers depending on the size of register_t. > > Modified: > head/sys/compat/cloudabi/cloudabi_clock.c > > Modified: head/sys/compat/cloudabi/cloudabi_clock.c > ============================================================================== > --- head/sys/compat/cloudabi/cloudabi_clock.c Sun Aug 21 07:28:38 2016 (r304554) > +++ head/sys/compat/cloudabi/cloudabi_clock.c Sun Aug 21 07:41:11 2016 (r304555) > @@ -117,7 +117,7 @@ cloudabi_sys_clock_res_get(struct thread > error = cloudabi_convert_timespec(&ts, &cts); > if (error != 0) > return (error); > - td->td_retval[0] = cts; > + memcpy(td->td_retval, &cts, sizeof(cts)); > return (0); > } > > @@ -129,6 +129,6 @@ cloudabi_sys_clock_time_get(struct threa > int error; > > error = cloudabi_clock_time_get(td, uap->clock_id, &ts); > - td->td_retval[0] = ts; > + memcpy(td->td_retval, &ts, sizeof(ts)); > return (error); Why do not use more simple solution: *(cloudabi_timestamp_t *)td->td_retval = cts; This is eliminate call to memcpy and allow compiler to use most effeicient way.
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