On 21/12/15 13:37, Will Deacon wrote: > On Mon, Dec 21, 2015 at 01:58:30PM +0100, Ard Biesheuvel wrote: >> On 21 December 2015 at 13:51, Will Deacon <will.dea...@arm.com> wrote: >>> On Mon, Dec 21, 2015 at 01:46:22PM +0100, Ard Biesheuvel wrote: >>>> On 21 December 2015 at 13:38, Will Deacon <will.dea...@arm.com> wrote: >>>>> On Fri, Dec 18, 2015 at 08:17:35PM -0800, Andrew Pinski wrote: >>>>>> The problem here is that GCC 6 and above emits .arch now >>>>>> for each function so now the global .arch_extension has >>>>>> no effect. This fixes the problem by putting >>>>>> .arch_extension inside ARM64_LSE_ATOMIC_INSN so >>>>>> it is enabled for each place where LSE is used. >>>>> >>>>> Hmm, this is going to affect arch/arm/ much more heavily than arch/arm64. >>>>> .arch_extension is used for virt, mp and sec over there, and it may be >>>>> tricky to isolate the actual instruction usage (at least, virt looks >>>>> lost in kvm/arm.c). >>>>> >>>>> Why can't gas have an option to accept all instruction encodings that it >>>>> knows about, inspite of any .arch directives? >>>>> >>>> >>>> Modern GAS supports things like -march=armv7-a+mp+sec+virt, so it >>>> probably makes sense to pass that on the command line when building >>>> for v7 (or +sec only for v6) if the assembler is found to support it >>>> at build time. >>> >>> Does that override a more restrictive .arch directive emitted by the >>> compiler? >>> >> >> It seems to be additive: -march=armv7-a+mp+sec allows a .S file >> containing a virt arch_extension + both hvc and smc instructions to be >> assembled. > > The problem I'm seeing is if I have something like: > > .arch_extension lse > > before something like: > > .cpu cortex-a57+fp+simd+crc > > -or- > > .arch armv8-a+fp+simd+crc > > then I can no longer assemble lse instructions. So the .cpu/.arch > directive is undoing the .arch_extension. We can fix this by following > Andrew's suggestion to have .arch_extension before every point of use, > but the whole thing would be much simpler if we could just tell gas to > assemble harder. > > Maybe we just need to construct the mother of all -march options based > on build-time checks in the Makefile? >
Since I've been bitten by this I'm curious what was conclusion on this topic? Thanks Vladimir > Will > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-ker...@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > >
