Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] x86: work around clang IAS bug referencing __force_order | Date | Thu, 13 Aug 2020 19:28:57 +0200 |
| |
Nick Desaulniers <ndesaulniers@google.com> writes: > On Thu, Aug 6, 2020 at 3:11 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> > + * >> > + * Clang sometimes fails to kill the reference to the dummy variable, so >> > + * provide an actual copy. >> >> Can that compiler be fixed instead? > > I don't think so. The logic in the compiler whether to emit an
Forget that I asked. Heat induced brain damaged.
> I'd much rather remove all of __force_order.
Right.
> Not sure about the comment in arch/x86/include/asm/special_insns.h > either; smells fishy like a bug with a compiler from a long time ago. > It looks like it was introduced in: > commit d3ca901f94b32 ("x86: unify paravirt parts of system.h") > Lore has this thread: > https://lore.kernel.org/lkml/4755A809.4050305@qumranet.com/ > Patch 4: https://lore.kernel.org/lkml/11967844071346-git-send-email-gcosta@redhat.com/ > It seems like there was a discussion about %cr8, but no one asked > "what's going on here with __force_order, is that right?"
Correct and the changelog is uselss in this regard.
> Quick boot test of the below works for me, though I should probably > test hosting a virtualized guest since d3ca901f94b32 refers to > paravirt. Thoughts?
Let me ask (hopefully) useful questions this time:
Is a compiler allowed to reorder two 'asm volatile()'?
Are there compilers (gcc >= 4.9 or other supported ones) which do that?
Thanks,
tglx
| |