Messages in this thread | | | From | Arvind Sankar <> | Date | Tue, 25 Aug 2020 11:19:10 -0400 | Subject | Re: [PATCH] x86/asm: Replace __force_order with memory clobber |
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On Mon, Aug 24, 2020 at 09:13:34PM +0200, Miguel Ojeda wrote: > Hi Arvind, > > On Sun, Aug 23, 2020 at 11:25 PM Arvind Sankar <nivedita@alum.mit.edu> wrote: > > > > - Using a dummy input operand with an arbitrary constant address for the > > read functions, instead of a global variable. This will prevent reads > > from being reordered across writes, while allowing memory loads to be > > cached/reordered across CRn reads, which should be safe. > > Assuming no surprises from compilers, this looks better than dealing > with different code for each compiler. > > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> > > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602 > > A lore link to the other discussion would be nice here for context. >
Ok.
> > + * The compiler should not reorder volatile asm, however older versions of GCC > > + * had a bug (which was fixed in 8.1, 7.3 and 6.5) where they could sometimes > > I'd mention the state of GCC 5 here. >
Ok.
> > + * reorder volatile asm. The write functions are not a problem since they have > > + * memory clobbers preventing reordering. To prevent reads from being reordered > > + * with respect to writes, use a dummy memory operand. > > */ > > -extern unsigned long __force_order; > > + > > Spurious newline? >
This was intentional, but I can remove it if people don't like the extra whitespace.
I'll wait a few days for additional review comments before sending v2.
Thanks.
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