| Message ID | CAKv+Gu9fc_F1iC5NAwaG_ed3RRhYnxEBLbuLgW0Oa_qJ96j-gA@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 01/28/2015 01:17 PM, Ard Biesheuvel wrote: > On 28 January 2015 at 17:20, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >> On 28 January 2015 at 17:08, Alex Elder <elder@linaro.org> wrote: >>> On 01/28/2015 10:17 AM, Ard Biesheuvel wrote: >>>> On 28 January 2015 at 14:11, Alex Elder <elder@linaro.org> wrote: >>>>> On 01/28/2015 05:15 AM, Ard Biesheuvel wrote: >>>>>> On 28 January 2015 at 05:18, Behan Webster <behanw@converseincode.com> wrote: >>>>>>> From: Alex Elder <elder@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 <elder@linaro.org> >>>>>>> Signed-off-by: Behan Webster <behanw@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? -Alex > -------->8---------- > diff --git a/arch/arm/include/asm/compiler.h b/arch/arm/include/asm/compiler.h > index 8155db2f7fa1..f99c674b3751 100644 > --- a/arch/arm/include/asm/compiler.h > +++ b/arch/arm/include/asm/compiler.h > @@ -9,7 +9,8 @@ > * will cause compilation to stop on mismatch. > * (for details, see gcc PR 15089) > */ > -#define __asmeq(x, y) ".ifnc " x "," y " ; .err ; .endif\n\t" > +#define __asmeq(x, y) ".ifnc " x "," y " ; .ifnc " x y ",ipr12 ; " \ > + ".ifnc " x y ",r12ip ; .err ; .endif ; .endif ; .endif\n\t" > > > #endif /* __ASM_ARM_COMPILER_H */ > -------->8---------- >
On 28 January 2015 at 19:27, Alex Elder <elder@linaro.org> wrote: > On 01/28/2015 01:17 PM, Ard Biesheuvel wrote: >> On 28 January 2015 at 17:20, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >>> On 28 January 2015 at 17:08, Alex Elder <elder@linaro.org> wrote: >>>> On 01/28/2015 10:17 AM, Ard Biesheuvel wrote: >>>>> On 28 January 2015 at 14:11, Alex Elder <elder@linaro.org> wrote: >>>>>> On 01/28/2015 05:15 AM, Ard Biesheuvel wrote: >>>>>>> On 28 January 2015 at 05:18, Behan Webster <behanw@converseincode.com> wrote: >>>>>>>> From: Alex Elder <elder@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 <elder@linaro.org> >>>>>>>> Signed-off-by: Behan Webster <behanw@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)
On 28 January 2015 at 19:38, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > On 28 January 2015 at 19:27, Alex Elder <elder@linaro.org> wrote: >> On 01/28/2015 01:17 PM, Ard Biesheuvel wrote: >>> On 28 January 2015 at 17:20, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: >>>> On 28 January 2015 at 17:08, Alex Elder <elder@linaro.org> wrote: >>>>> On 01/28/2015 10:17 AM, Ard Biesheuvel wrote: >>>>>> On 28 January 2015 at 14:11, Alex Elder <elder@linaro.org> wrote: >>>>>>> On 01/28/2015 05:15 AM, Ard Biesheuvel wrote: >>>>>>>> On 28 January 2015 at 05:18, Behan Webster <behanw@converseincode.com> wrote: >>>>>>>>> From: Alex Elder <elder@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 <elder@linaro.org> >>>>>>>>> Signed-off-by: Behan Webster <behanw@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) > Actually, if clang is guaranteed to emit the correct register name inside the inline asm for register asm variables used in input or output constraints, I think it makes sense to #define __asmeq as a nop if __clang__ is defined. (Note that __asmeq only exists to work around a specific GCC bug)
On 01/28/2015 02:11 PM, Ard Biesheuvel wrote: > Actually, if clang is guaranteed to emit the correct register name > inside the inline asm for register asm variables used in input or > output constraints, I think it makes sense to #define __asmeq as a nop > if __clang__ is defined. (Note that __asmeq only exists to work around > a specific GCC bug) I agree completely. Behan, what do you think? -Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/arch/arm/include/asm/compiler.h b/arch/arm/include/asm/compiler.h index 8155db2f7fa1..f99c674b3751 100644 --- a/arch/arm/include/asm/compiler.h +++ b/arch/arm/include/asm/compiler.h @@ -9,7 +9,8 @@ * will cause compilation to stop on mismatch. * (for details, see gcc PR 15089) */ -#define __asmeq(x, y) ".ifnc " x "," y " ; .err ; .endif\n\t" +#define __asmeq(x, y) ".ifnc " x "," y " ; .ifnc " x y ",ipr12 ; " \ + ".ifnc " x y ",r12ip ; .err ; .endif ; .endif ; .endif\n\t" #endif /* __ASM_ARM_COMPILER_H */