Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] x86: work around clang IAS bug referencing __force_order | Date | Thu, 20 Aug 2020 12:44:06 +0200 |
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On Thu, Aug 13 2020 at 14:09, Arvind Sankar wrote: > On Thu, Aug 13, 2020 at 10:37:01AM -0700, Paul E. McKenney wrote: >> > 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? >> >> I would hope that the answer to both of these questions is "no"! >> >> But I freely confess that I have been disappointed before on this sort >> of thing. :-/ >> >> Thanx, Paul > > Ok, I found this, so gcc developers consider re-ordering volatile asm > wrt each other a bug at least. > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82602
Yes. It prevents reordering of volatiles, but it does not necessarily prevent reorder of something like this:
asm volatile(...); foo(); asm volatile(...);
it might turn that into
foo(); asm volatile(...); asm volatile(...);
if I understood their discussion correctly. So removing this magic is not really straight forward.
Thanks,
tglx
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