* Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-15 3:46 Yangfei (Felix)
2012-10-15 7:28 ` Mikael Pettersson
0 siblings, 1 reply; 6+ messages in thread
From: Yangfei (Felix) @ 2012-10-15 3:46 UTC (permalink / raw)
To: linux-assembly@vger.kernel.org; +Cc: linux-kernel@vger.kernel.org
Hi all,
I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness.
As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c:
/ *
* here's the WFI
*/
asm(".word 0xe320f003\n"
:
:
: "memory", "cc");
The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated.
Here the code should be:
/ *
* here's the WFI
*/
asm("WFI\n"
:
:
: "memory", "cc");
Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens.
Can anyone tell me who owns this part? I can prepare a patch then.
Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness 2012-10-15 3:46 Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Yangfei (Felix) @ 2012-10-15 7:28 ` Mikael Pettersson 2012-10-15 15:33 ` [PATCH] " Fei Yang 0 siblings, 1 reply; 6+ messages in thread From: Mikael Pettersson @ 2012-10-15 7:28 UTC (permalink / raw) To: Yangfei (Felix) Cc: linux-assembly@vger.kernel.org, linux-kernel@vger.kernel.org Yangfei (Felix) writes: > Hi all, > > I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness. > As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c: > / * > * here's the WFI > */ > asm(".word 0xe320f003\n" > : > : > : "memory", "cc"); > > The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated. > > Here the code should be: > / * > * here's the WFI > */ > asm("WFI\n" > : > : > : "memory", "cc"); > > Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens. > Can anyone tell me who owns this part? I can prepare a patch then. > Thanks. Questions regarding the ARM kernel should go to the linux-arm-kernel mailing list (see the MAINTAINERS file), with an optional cc: to the regular LKML. BE-8 is, if I recall correctly, ARMv7's broken format where code and data have different endianess. GAS supports an ".inst" directive which is like ".word" except the data is assumed to be code. This matters for disassembly, and may also be required for BE-8. That is, just s/.word/.inst/g above and report back if that works or not. ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness 2012-10-15 7:28 ` Mikael Pettersson @ 2012-10-15 15:33 ` Fei Yang 2012-10-16 12:49 ` Dave Martin 0 siblings, 1 reply; 6+ messages in thread From: Fei Yang @ 2012-10-15 15:33 UTC (permalink / raw) To: Mikael Pettersson, linux, lethal, magnus.damm, kgene.kim, linux-arm-kernel Cc: linux-hotplug, linux-assembly@vger.kernel.org, linux-kernel@vger.kernel.org, Yangfei (Felix) 2012/10/15 Mikael Pettersson <mikpe@it.uu.se>: > Yangfei (Felix) writes: > > Hi all, > > > > I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness. > > As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c: > > / * > > * here's the WFI > > */ > > asm(".word 0xe320f003\n" > > : > > : > > : "memory", "cc"); > > > > The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated. > > > > Here the code should be: > > / * > > * here's the WFI > > */ > > asm("WFI\n" > > : > > : > > : "memory", "cc"); > > > > Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens. > > Can anyone tell me who owns this part? I can prepare a patch then. > > Thanks. > > Questions regarding the ARM kernel should go to the linux-arm-kernel mailing list > (see the MAINTAINERS file), with an optional cc: to the regular LKML. > > BE-8 is, if I recall correctly, ARMv7's broken format where code and data have > different endianess. GAS supports an ".inst" directive which is like ".word" > except the data is assumed to be code. This matters for disassembly, and may > also be required for BE-8. > > That is, just s/.word/.inst/g above and report back if that works or not. > -- > 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/ > > Hi Mikael, Thanks for the reply. I modified the code as suggested and rebuilt the kernel, cpu-hotplug feature now works on big-endian(BE-8) ARM platform. Since the ARM core can be configured by system software to work in big-endian mode, it's necessary to fix this problem. And here is a small patch : diff -urN linux-3.6.2/arch/arm/mach-exynos/hotplug.c linux/arch/arm/mach-exynos/hotplug.c --- linux-3.6.2/arch/arm/mach-exynos/hotplug.c 2012-10-13 04:50:59.000000000 +0800 +++ linux/arch/arm/mach-exynos/hotplug.c 2012-10-15 23:05:44.000000000 +0800 @@ -72,7 +72,7 @@ /* * here's the WFI */ - asm(".word 0xe320f003\n" + asm(".inst 0xe320f003\n" : : : "memory", "cc"); diff -urN linux-3.6.2/arch/arm/mach-realview/hotplug.c linux/arch/arm/mach-realview/hotplug.c --- linux-3.6.2/arch/arm/mach-realview/hotplug.c 2012-10-13 04:50:59.000000000 +0800 +++ linux/arch/arm/mach-realview/hotplug.c 2012-10-15 23:05:00.000000000 +0800 @@ -66,7 +66,7 @@ /* * here's the WFI */ - asm(".word 0xe320f003\n" + asm(".inst 0xe320f003\n" : : : "memory", "cc"); diff -urN linux-3.6.2/arch/arm/mach-shmobile/hotplug.c linux/arch/arm/mach-shmobile/hotplug.c --- linux-3.6.2/arch/arm/mach-shmobile/hotplug.c 2012-10-13 04:50:59.000000000 +0800 +++ linux/arch/arm/mach-shmobile/hotplug.c 2012-10-15 23:05:25.000000000 +0800 @@ -53,7 +53,7 @@ /* * here's the WFI */ - asm(".word 0xe320f003\n" + asm(".inst 0xe320f003\n" : : : "memory", "cc"); ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness 2012-10-15 15:33 ` [PATCH] " Fei Yang @ 2012-10-16 12:49 ` Dave Martin 2012-10-16 16:33 ` Fei Yang 0 siblings, 1 reply; 6+ messages in thread From: Dave Martin @ 2012-10-16 12:49 UTC (permalink / raw) To: Fei Yang Cc: Mikael Pettersson, linux, lethal, magnus.damm, kgene.kim, linux-arm-kernel, linux-assembly@vger.kernel.org, linux-hotplug, linux-kernel@vger.kernel.org, Yangfei (Felix) On Mon, Oct 15, 2012 at 11:33:08PM +0800, Fei Yang wrote: > 2012/10/15 Mikael Pettersson <mikpe@it.uu.se>: > > Yangfei (Felix) writes: > > > Hi all, > > > > > > I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness. > > > As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c: > > > / * > > > * here's the WFI > > > */ > > > asm(".word 0xe320f003\n" > > > : > > > : > > > : "memory", "cc"); > > > > > > The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated. > > > > > > Here the code should be: > > > / * > > > * here's the WFI > > > */ > > > asm("WFI\n" > > > : > > > : > > > : "memory", "cc"); > > > > > > Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens. > > > Can anyone tell me who owns this part? I can prepare a patch then. > > > Thanks. > > > > Questions regarding the ARM kernel should go to the linux-arm-kernel mailing list > > (see the MAINTAINERS file), with an optional cc: to the regular LKML. > > > > BE-8 is, if I recall correctly, ARMv7's broken format where code and data have > > different endianess. GAS supports an ".inst" directive which is like ".word" > > except the data is assumed to be code. This matters for disassembly, and may > > also be required for BE-8. > > > > That is, just s/.word/.inst/g above and report back if that works or not. > > -- > > 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/ > > > > > > Hi Mikael, > > Thanks for the reply. I modified the code as suggested and rebuilt the > kernel, cpu-hotplug feature now works on big-endian(BE-8) ARM > platform. > Since the ARM core can be configured by system software to work in > big-endian mode, it's necessary to fix this problem. And here is a > small patch : > > diff -urN linux-3.6.2/arch/arm/mach-exynos/hotplug.c > linux/arch/arm/mach-exynos/hotplug.c > --- linux-3.6.2/arch/arm/mach-exynos/hotplug.c 2012-10-13 > 04:50:59.000000000 +0800 > +++ linux/arch/arm/mach-exynos/hotplug.c 2012-10-15 23:05:44.000000000 +0800 > @@ -72,7 +72,7 @@ > /* > * here's the WFI > */ > - asm(".word 0xe320f003\n" > + asm(".inst 0xe320f003\n" The cleanest fix would simply be to build these files with appropriate modified CFLAGS (-march=armv6k or -march=armv7-a), and use the proper "wfi" mnemonic. Failing that, you could use the facilities in <asm/opcodes.h> to declare a wrapper macro for injecting this opcode (see <asm/opcodes-virt.h> for an example). However, putting custom opcodes into the assembler should only be done if it's really necessary. Nowadays, I think we can consider tools which don't understand the WFI mnemonic to be obsolete, at least for platforms which only build for v7 and above. The relevant board maintainers would need to sign off on such a change, so we don't end up breaking their builds. If any of these boards needs to build for v6K, the custom opcode might be worth it -- some people might just possibly be relying on older tools for such platforms. Cheers ---Dave > : > : > : "memory", "cc"); > diff -urN linux-3.6.2/arch/arm/mach-realview/hotplug.c > linux/arch/arm/mach-realview/hotplug.c > --- linux-3.6.2/arch/arm/mach-realview/hotplug.c 2012-10-13 > 04:50:59.000000000 +0800 > +++ linux/arch/arm/mach-realview/hotplug.c 2012-10-15 23:05:00.000000000 +0800 > @@ -66,7 +66,7 @@ > /* > * here's the WFI > */ > - asm(".word 0xe320f003\n" > + asm(".inst 0xe320f003\n" > : > : > : "memory", "cc"); > diff -urN linux-3.6.2/arch/arm/mach-shmobile/hotplug.c > linux/arch/arm/mach-shmobile/hotplug.c > --- linux-3.6.2/arch/arm/mach-shmobile/hotplug.c 2012-10-13 > 04:50:59.000000000 +0800 > +++ linux/arch/arm/mach-shmobile/hotplug.c 2012-10-15 23:05:25.000000000 +0800 > @@ -53,7 +53,7 @@ > /* > * here's the WFI > */ > - asm(".word 0xe320f003\n" > + asm(".inst 0xe320f003\n" > : > : > : "memory", "cc"); > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness 2012-10-16 12:49 ` Dave Martin @ 2012-10-16 16:33 ` Fei Yang 2012-10-16 17:25 ` Dave Martin 0 siblings, 1 reply; 6+ messages in thread From: Fei Yang @ 2012-10-16 16:33 UTC (permalink / raw) To: Dave Martin Cc: Mikael Pettersson, linux, lethal, magnus.damm, kgene.kim, linux-arm-kernel, linux-assembly@vger.kernel.org, linux-hotplug, linux-kernel@vger.kernel.org, Yangfei (Felix) 2012/10/16 Dave Martin <dave.martin@linaro.org>: > On Mon, Oct 15, 2012 at 11:33:08PM +0800, Fei Yang wrote: >> 2012/10/15 Mikael Pettersson <mikpe@it.uu.se>: >> > Yangfei (Felix) writes: >> > > Hi all, >> > > >> > > I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness. >> > > As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c: >> > > / * >> > > * here's the WFI >> > > */ >> > > asm(".word 0xe320f003\n" >> > > : >> > > : >> > > : "memory", "cc"); >> > > >> > > The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated. >> > > >> > > Here the code should be: >> > > / * >> > > * here's the WFI >> > > */ >> > > asm("WFI\n" >> > > : >> > > : >> > > : "memory", "cc"); >> > > >> > > Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens. >> > > Can anyone tell me who owns this part? I can prepare a patch then. >> > > Thanks. >> > >> > Questions regarding the ARM kernel should go to the linux-arm-kernel mailing list >> > (see the MAINTAINERS file), with an optional cc: to the regular LKML. >> > >> > BE-8 is, if I recall correctly, ARMv7's broken format where code and data have >> > different endianess. GAS supports an ".inst" directive which is like ".word" >> > except the data is assumed to be code. This matters for disassembly, and may >> > also be required for BE-8. >> > >> > That is, just s/.word/.inst/g above and report back if that works or not. >> > -- >> > 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/ >> > >> > >> >> Hi Mikael, >> >> Thanks for the reply. I modified the code as suggested and rebuilt the >> kernel, cpu-hotplug feature now works on big-endian(BE-8) ARM >> platform. >> Since the ARM core can be configured by system software to work in >> big-endian mode, it's necessary to fix this problem. And here is a >> small patch : >> >> diff -urN linux-3.6.2/arch/arm/mach-exynos/hotplug.c >> linux/arch/arm/mach-exynos/hotplug.c >> --- linux-3.6.2/arch/arm/mach-exynos/hotplug.c 2012-10-13 >> 04:50:59.000000000 +0800 >> +++ linux/arch/arm/mach-exynos/hotplug.c 2012-10-15 23:05:44.000000000 +0800 >> @@ -72,7 +72,7 @@ >> /* >> * here's the WFI >> */ >> - asm(".word 0xe320f003\n" >> + asm(".inst 0xe320f003\n" > > The cleanest fix would simply be to build these files with appropriate > modified CFLAGS (-march=armv6k or -march=armv7-a), and use the proper > "wfi" mnemonic. > > Failing that, you could use the facilities in <asm/opcodes.h> to > declare a wrapper macro for injecting this opcode (see > <asm/opcodes-virt.h> for an example). However, putting custom > opcodes into the assembler should only be done if it's really > necessary. Nowadays, I think we can consider tools which don't > understand the WFI mnemonic to be obsolete, at least for platforms > which only build for v7 and above. > > The relevant board maintainers would need to sign off on such a > change, so we don't end up breaking their builds. > > If any of these boards needs to build for v6K, the custom opcode might > be worth it -- some people might just possibly be relying on older tools > for such platforms. > > Cheers > ---Dave > >> : >> : >> : "memory", "cc"); >> diff -urN linux-3.6.2/arch/arm/mach-realview/hotplug.c >> linux/arch/arm/mach-realview/hotplug.c >> --- linux-3.6.2/arch/arm/mach-realview/hotplug.c 2012-10-13 >> 04:50:59.000000000 +0800 >> +++ linux/arch/arm/mach-realview/hotplug.c 2012-10-15 23:05:00.000000000 +0800 >> @@ -66,7 +66,7 @@ >> /* >> * here's the WFI >> */ >> - asm(".word 0xe320f003\n" >> + asm(".inst 0xe320f003\n" >> : >> : >> : "memory", "cc"); >> diff -urN linux-3.6.2/arch/arm/mach-shmobile/hotplug.c >> linux/arch/arm/mach-shmobile/hotplug.c >> --- linux-3.6.2/arch/arm/mach-shmobile/hotplug.c 2012-10-13 >> 04:50:59.000000000 +0800 >> +++ linux/arch/arm/mach-shmobile/hotplug.c 2012-10-15 23:05:25.000000000 +0800 >> @@ -53,7 +53,7 @@ >> /* >> * here's the WFI >> */ >> - asm(".word 0xe320f003\n" >> + asm(".inst 0xe320f003\n" >> : >> : >> : "memory", "cc"); >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel Thanks for the suggestions. The ".inst" directive here may also bring us trouble if some older tools is used. In that situation, "wfi" mnemonic will not be recognized either. If we cannot suppose that newer tools is used, then how can we determine the endianness during the preprocessor/compile phase? Any ideas? BTW: I found this bug on my ARM V7-A Cortex-A9 board and the processor is configured to work in big-endian mode at boot stage (word and halfword data is interpreted as big-endian, but instruction is still little-endian) . The kernel is ported from arch/arm/mach-realview. And I think these boards(mach-realview/mach-shmobile/mach-exynos) should have the similar problems. ARM arch is Bi-endian since versions 3 and above. ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness 2012-10-16 16:33 ` Fei Yang @ 2012-10-16 17:25 ` Dave Martin 0 siblings, 0 replies; 6+ messages in thread From: Dave Martin @ 2012-10-16 17:25 UTC (permalink / raw) To: Fei Yang Cc: Mikael Pettersson, linux, lethal, magnus.damm, kgene.kim, linux-arm-kernel, linux-assembly@vger.kernel.org, linux-hotplug, linux-kernel@vger.kernel.org, Yangfei (Felix) On Wed, Oct 17, 2012 at 12:33:54AM +0800, Fei Yang wrote: > 2012/10/16 Dave Martin <dave.martin@linaro.org>: > > On Mon, Oct 15, 2012 at 11:33:08PM +0800, Fei Yang wrote: > >> 2012/10/15 Mikael Pettersson <mikpe@it.uu.se>: > >> > Yangfei (Felix) writes: > >> > > Hi all, > >> > > > >> > > I found that hardcoded instruction in inline asm can cause certains certain features fail to work on ARM platform due to endianness. > >> > > As an example, consider the following code snippet of platform_do_lowpower function from arch/arm/mach-realview/hotplug.c: > >> > > / * > >> > > * here's the WFI > >> > > */ > >> > > asm(".word 0xe320f003\n" > >> > > : > >> > > : > >> > > : "memory", "cc"); > >> > > > >> > > The instruction generated from this inline asm will not work on big-endian ARM platform, such as ARM BE-8 format. Instead, an exception will be generated. > >> > > > >> > > Here the code should be: > >> > > / * > >> > > * here's the WFI > >> > > */ > >> > > asm("WFI\n" > >> > > : > >> > > : > >> > > : "memory", "cc"); > >> > > > >> > > Seems the kernel doesn't support ARM BE-8 well. I don't know why this problem happens. > >> > > Can anyone tell me who owns this part? I can prepare a patch then. > >> > > Thanks. > >> > > >> > Questions regarding the ARM kernel should go to the linux-arm-kernel mailing list > >> > (see the MAINTAINERS file), with an optional cc: to the regular LKML. > >> > > >> > BE-8 is, if I recall correctly, ARMv7's broken format where code and data have > >> > different endianess. GAS supports an ".inst" directive which is like ".word" > >> > except the data is assumed to be code. This matters for disassembly, and may > >> > also be required for BE-8. > >> > > >> > That is, just s/.word/.inst/g above and report back if that works or not. > >> > -- > >> > 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/ > >> > > >> > > >> > >> Hi Mikael, > >> > >> Thanks for the reply. I modified the code as suggested and rebuilt the > >> kernel, cpu-hotplug feature now works on big-endian(BE-8) ARM > >> platform. > >> Since the ARM core can be configured by system software to work in > >> big-endian mode, it's necessary to fix this problem. And here is a > >> small patch : > >> > >> diff -urN linux-3.6.2/arch/arm/mach-exynos/hotplug.c > >> linux/arch/arm/mach-exynos/hotplug.c > >> --- linux-3.6.2/arch/arm/mach-exynos/hotplug.c 2012-10-13 > >> 04:50:59.000000000 +0800 > >> +++ linux/arch/arm/mach-exynos/hotplug.c 2012-10-15 23:05:44.000000000 +0800 > >> @@ -72,7 +72,7 @@ > >> /* > >> * here's the WFI > >> */ > >> - asm(".word 0xe320f003\n" > >> + asm(".inst 0xe320f003\n" > > > > The cleanest fix would simply be to build these files with appropriate > > modified CFLAGS (-march=armv6k or -march=armv7-a), and use the proper > > "wfi" mnemonic. > > > > Failing that, you could use the facilities in <asm/opcodes.h> to > > declare a wrapper macro for injecting this opcode (see > > <asm/opcodes-virt.h> for an example). However, putting custom > > opcodes into the assembler should only be done if it's really > > necessary. Nowadays, I think we can consider tools which don't > > understand the WFI mnemonic to be obsolete, at least for platforms > > which only build for v7 and above. > > > > The relevant board maintainers would need to sign off on such a > > change, so we don't end up breaking their builds. > > > > If any of these boards needs to build for v6K, the custom opcode might > > be worth it -- some people might just possibly be relying on older tools > > for such platforms. > > > > Cheers > > ---Dave > > > >> : > >> : > >> : "memory", "cc"); > >> diff -urN linux-3.6.2/arch/arm/mach-realview/hotplug.c > >> linux/arch/arm/mach-realview/hotplug.c > >> --- linux-3.6.2/arch/arm/mach-realview/hotplug.c 2012-10-13 > >> 04:50:59.000000000 +0800 > >> +++ linux/arch/arm/mach-realview/hotplug.c 2012-10-15 23:05:00.000000000 +0800 > >> @@ -66,7 +66,7 @@ > >> /* > >> * here's the WFI > >> */ > >> - asm(".word 0xe320f003\n" > >> + asm(".inst 0xe320f003\n" > >> : > >> : > >> : "memory", "cc"); > >> diff -urN linux-3.6.2/arch/arm/mach-shmobile/hotplug.c > >> linux/arch/arm/mach-shmobile/hotplug.c > >> --- linux-3.6.2/arch/arm/mach-shmobile/hotplug.c 2012-10-13 > >> 04:50:59.000000000 +0800 > >> +++ linux/arch/arm/mach-shmobile/hotplug.c 2012-10-15 23:05:25.000000000 +0800 > >> @@ -53,7 +53,7 @@ > >> /* > >> * here's the WFI > >> */ > >> - asm(".word 0xe320f003\n" > >> + asm(".inst 0xe320f003\n" > >> : > >> : > >> : "memory", "cc"); > >> > >> _______________________________________________ > >> linux-arm-kernel mailing list > >> linux-arm-kernel@lists.infradead.org > >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > Thanks for the suggestions. The ".inst" directive here may also bring > us trouble if some older tools is used. > In that situation, "wfi" mnemonic will not be recognized either. If we > cannot suppose that newer tools is used, then how can we determine the > endianness during the preprocessor/compile phase? Any ideas? The endianness is controlled by the build-time configuration of the kernel. A single kernel image cannot be bi-endian. The __inst_*() macros in <asm/opcodes.h> take care of this based on which CONFIG_CPU_ENDIAN_* option is selected by the board in the kernel config. For compatibility with old tools, this is done instead of using the ".inst" directive. > BTW: I found this bug on my ARM V7-A Cortex-A9 board and the processor > is configured to work in big-endian mode at boot stage (word and > halfword data is interpreted as big-endian, but instruction is still > little-endian) . The kernel is ported from arch/arm/mach-realview. And > I think these boards(mach-realview/mach-shmobile/mach-exynos) should > have the similar problems. ARM arch is Bi-endian since versions 3 and > above. I believe that shmobile and exynos are v7-only, so it may be better to just use "wfi" and override the CFLAGS for those files. As you can see, those were just created by copy-pasting the code from mach-realview. realview itself can be used with ARMv6 based core-tiles, so there may be an argument for a custom opcode in this case: #include <asm/opcodes.h> #define __WFI __inst_arm_thumb16(0xE320F003, 0xBF30) Not handling the Thumb case is a definite bug for any file which may run on v7, since the kernel could be built in Thumb for that case. For example, the existing code is mach-realview/hotplug.c is broken when building an SMP Thumb-2 kernel for the Realview PBX-A9. Cheers ---Dave ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2012-10-16 17:25 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2012-10-15 3:46 Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Yangfei (Felix) 2012-10-15 7:28 ` Mikael Pettersson 2012-10-15 15:33 ` [PATCH] " Fei Yang 2012-10-16 12:49 ` Dave Martin 2012-10-16 16:33 ` Fei Yang 2012-10-16 17:25 ` Dave Martin
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