On Wed, Mar 4, 2020 at 3:27 AM Guido Falsi <madpi...@freebsd.org> wrote: > > On 02/03/20 18:13, Ryan Libby wrote: > > On Mon, Mar 2, 2020 at 12:45 AM Alexander V. Chernikov <melif...@ipfw.ru> > > wrote: > >> > >> 28.02.2020, 18:32, "Ryan Libby" <rli...@freebsd.org>: > >>> Author: rlibby > >>> Date: Fri Feb 28 18:32:36 2020 > >>> New Revision: 358439 > >>> URL: https://svnweb.freebsd.org/changeset/base/358439 > >>> > >>> Log: > >>> amd64 atomic.h: minor codegen optimization in flag access > >>> > >>> Previously the pattern to extract status flags from inline assembly > >>> blocks was to use setcc in the block to write the flag to a register. > >>> This was suboptimal in a few ways: > >>> - It would lead to code like: sete %cl; test %cl; jne, i.e. a flag > >>> would just be loaded into a register and then reloaded to a flag. > >>> - The setcc would force the block to use an additional register. > >>> - If the client code didn't care for the flag value then the setcc > >>> would be entirely pointless but could not be eliminated by the > >>> optimizer. > >>> > >>> A more modern inline asm construct (since gcc 6 and clang 9) allows for > >> This effectively restricts kernel builds by all older compilers. > >> Is there any chance of making it conditional depending on the compiler > >> version/features? > > > > Yes, it is possible to test for __GCC_ASM_FLAG_OUTPUTS__. It is more > > maintenance effort going forward. If building current with an old cross > > compiler is an important scenario, we can either revert this and the > > following revision or work up a patch to make it conditional. I'll see > > what that might look like. > > > > Actually this causes emulators/virtualbox-ose port to fail to build: > > In file included from /usr/src/sys/sys/systm.h:44: > /usr/include/machine/atomic.h:230:1: error: invalid output constraint > '=@cce' in asm > ATOMIC_CMPSET(char); > ^ > /usr/include/machine/atomic.h:205:4: note: expanded from macro > 'ATOMIC_CMPSET' > : "=@cce" (res), /* 0 */ \ > ^ > /usr/include/machine/atomic.h:230:1: error: invalid output constraint > '=@cce' in asm > > (and so on) > > > the virtualbox-ose port is forced to use an older clang version due to > crashes when compiled with newer ones. > > Not sure whose responsibility is to fix this. > > Should I file a bug report on bugzilla? > > -- > Guido Falsi <madpi...@freebsd.org>
We've discussed whether to provide compatibility code for older compilers here: https://reviews.freebsd.org/D23937 There's a bug tracking virtualbox-ose being pinned to an old compiler here: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236616 I see you have commented on that bug. _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
