On 28 January 2015 at 19:27, Alex Elder <el...@linaro.org> wrote: > On 01/28/2015 01:17 PM, Ard Biesheuvel wrote: >> On 28 January 2015 at 17:20, Ard Biesheuvel <ard.biesheu...@linaro.org> >> wrote: >>> On 28 January 2015 at 17:08, Alex Elder <el...@linaro.org> wrote: >>>> On 01/28/2015 10:17 AM, Ard Biesheuvel wrote: >>>>> On 28 January 2015 at 14:11, Alex Elder <el...@linaro.org> wrote: >>>>>> On 01/28/2015 05:15 AM, Ard Biesheuvel wrote: >>>>>>> On 28 January 2015 at 05:18, Behan Webster <beh...@converseincode.com> >>>>>>> wrote: >>>>>>>> From: Alex Elder <el...@linaro.org> >>>>>>>> >>>>>>>> My GCC-based build environment likes to call register r12 by the >>>>>>>> name "ip" in inline asm. Behan Webster informed me that his Clang- >>>>>>>> based build environment likes "r12" instead. >>>>>>>> >>>>>>>> Try to make them both happy. >>>>>>>> >>>>>>>> Signed-off-by: Alex Elder <el...@linaro.org> >>>>>>>> Signed-off-by: Behan Webster <beh...@converseincode.com> >>>>>>>> --- >>>>>>>> arch/arm/mach-bcm/bcm_kona_smc.c | 9 +++++++-- >>>>>>>> 1 file changed, 7 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/arch/arm/mach-bcm/bcm_kona_smc.c >>>>>>>> b/arch/arm/mach-bcm/bcm_kona_smc.c >>>>>>>> index a55a7ec..3937bd5 100644 >>>>>>>> --- a/arch/arm/mach-bcm/bcm_kona_smc.c >>>>>>>> +++ b/arch/arm/mach-bcm/bcm_kona_smc.c >>>>>>>> @@ -106,9 +106,14 @@ int __init bcm_kona_smc_init(void) >>>>>>>> * request result appropriately. This result value is found in r0 >>>>>>>> * when the "smc" request completes. >>>>>>>> */ >>>>>>>> +#ifdef __clang__ >>>>>>>> +#define R12 "r12" >>>>>>>> +#else /* !__clang__ */ >>>>>>>> +#define R12 "ip" /* gcc calls r12 "ip" */ >>>>>>>> +#endif /* !__clang__ */ >>>>>>> >>>>>>> Why not just use r12 for both? >>>>>> >>>>>> Yes, that would have been an obvious fix. But the >>>>>> assembler (in the GCC environment) doesn't accept that. >>>>>> >>>>> >>>>> Mine has no problems with it at all >>>>> >>>>> $ echo 'mov r12, #0' | arm-linux-gnueabihf-gcc -c -x assembler-with-cpp - >>>>> >>>>> and grepping for r12 under arch/arm suggests the same >>>> >>>> The use of "r12" is fine. But it's not just the assembler, >>>> I believe it also involves gcc. >>>> >>>> The problem is with the use of the __asmeq(x, y) macro. >>>> >>> >>> Ah right. Apologies for assuming that you had missed something obvious here. >>> But __asmeq is not the toolchain, it is a local construct #define'd in >>> compiler.h >>> >>>> If I assign the "ip" variable with "r12": >>>> register u32 ip asm("r12"); /* Also called ip */ >>>> >>>> Then that's fine. However, this line then causes an error: >>>> __asmeq("%0", "r12") >>>> >>>> Apparently gcc uses register "ip" when it sees asm("r12"). So >>>> attempting to verify the desired register got used with __asmeq() >>>> causes a string mismatch--"ip" is not equal to "r12". >>>> >>>> So I could use: >>>> >>>> register u32 ip asm("r12"); /* Also called ip */ >>>> ... >>>> __asmeq("%0", "ip") >>>> >>>> And that will build. But it's a little non-intuitive, and >>>> I suspect that clang might (rightfully) have a failure in >>>> this __asmeq() call. >>>> >>> >>> In that case, I would strongly suggest fixing the __asmeq () macro >>> instead, and teach it that ("r12","ip") and ("ip","r12") are fine too. >>> >>> The thing is, inline asm is a dodgy area to begin with in terms of >>> clang-to-gcc compatibility. On arm64, we have been seeing issues where >>> the width of the register -which is fixed on gcc- is selected based on >>> the size of that variable, i.e., an int32 gets a w# register and int64 >>> gets a x# register. Imagine debugging that, e.g., a str %0, [xx] that >>> writes 8 bytes on GCC suddenly only writing 4 bytes when built with >>> clang. >>> >>> If we also start using the preprocessor to conditionalise what is >>> emitted by inline asm, the waters get even murkier and it becomes even >>> harder to claim parity between the two. >>> >> >> Something like this perhaps? > > So __asmeq() yields true if the register names (strings) are > equal, or if one is "ip" and the other is "r12" (in either order). > > I can't comment on whether it's right in all build environments but > this looks OK to me, to handle this special case. > > I would much rather you generate that patch. Is that OK? >
Sure, I can cook up a patch if you guys can confirm that it fixes your use case. (I tested GCC myself but I don't have clang installed) -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/