On Fri, Aug 21, 2020 at 02:37:48AM +0200, Thomas Gleixner wrote: > On Thu, Aug 20 2020 at 09:06, Arvind Sankar wrote: > > I don't think that's an issue, or at least, not one where force_order > > helps. > > > > If the source for foo() is not visible to the compiler, the only reason > > force_order prevents the reordering is because foo() might have > > references to it, but equally foo() might have volatile asm, so the > > reordering isn't possible anyway. > > > > If the source is visible, force_order won't prevent any reordering > > except across references to force_order, but the only references are > > from the volatile asm's which already prevent reordering. > > > > I think force_order can only help with buggy compilers, and for those it > > should really have been an input-output operand -- it wouldn't currently > > do anything to prevent cr writes from being reordered. > > Fair enough. Care to provide a patch which has the collected wisdom of > this thread in the changelog? > > Thanks, > > tglx
The gcc bug I linked to earlier is only fixed in gcc-6 onwards. Is that good enough to remove force_order? I can test gcc-4.9 and gcc-5 to check if it would currently have any impact. CBL guys, can you confirm that clang also will not reorder volatile asm? Thanks.
