On Wed, Sep 02, 2020 at 12:16:24PM -0500, Segher Boessenkool wrote: > On Wed, Sep 02, 2020 at 11:33:46AM -0400, Arvind Sankar wrote: > > The CRn accessor functions use __force_order as a dummy operand to > > prevent the compiler from reordering the inline asm. > > > > The fact that the asm is volatile should be enough to prevent this > > already, however older versions of GCC had a bug that could sometimes > > result in reordering. This was fixed in 8.1, 7.3 and 6.5. Versions prior > > to these, including 5.x and 4.9.x, may reorder volatile asm. > > Reordering them amongst themselves. Yes, that is bad. Reordering them > with "random" code is Just Fine.
Right, that's what I meant, but the text isn't clear. I will edit to clarify. > > Volatile asm should be executed on the real machine exactly as often as > on the C abstract machine, and in the same order. That is all. > > > + * The compiler should not reorder volatile asm, > > So, this comment needs work. And perhaps the rest of the patch as well? > > > Segher I think the patch itself is ok, we do only want to avoid reordering volatile asm vs volatile asm. But the comment needs clarification. Thanks.
