* 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; 15+ messages in thread
From: Yangfei (Felix) @ 2012-10-15 3:46 UTC (permalink / raw)
To: linux-assembly; +Cc: linux-kernel
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] 15+ 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 10:30 ` 答复: " Yangfei (Felix)
2012-10-15 15:33 ` Fei Yang
0 siblings, 2 replies; 15+ messages in thread
From: Mikael Pettersson @ 2012-10-15 7:28 UTC (permalink / raw)
To: Yangfei (Felix); +Cc: linux-assembly, linux-kernel
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] 15+ messages in thread
* 答复: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
2012-10-15 7:28 ` Mikael Pettersson
@ 2012-10-15 10:30 ` Yangfei (Felix)
2012-10-15 15:33 ` Fei Yang
1 sibling, 0 replies; 15+ messages in thread
From: Yangfei (Felix) @ 2012-10-15 10:30 UTC (permalink / raw)
To: linux-arm-kernel
Hi Mikael & Russell,
Thanks for the suggestions. I tried to replace ".word" with ".inst" and the cpu-hotplug feature now works on big-endian (BE-8) ARM platform. And illegal instruction exception disappears.
And the following is my small patch to fix the problem,
diff -urN linux-3.7-rc1/arch/arm/mach-exynos/hotplug.c linux/arch/arm/mach-exynos/hotplug.c
--- linux-3.7-rc1/arch/arm/mach-exynos/hotplug.c 2012-10-15 05:41:04.000000000 +0800
+++ linux/arch/arm/mach-exynos/hotplug.c 2012-10-15 17:47:28.177103266 +0800
@@ -72,7 +72,7 @@
/*
* here's the WFI
*/
- asm(".word 0xe320f003\n"
+ asm(".inst 0xe320f003\n"
:
:
: "memory", "cc");
diff -urN linux-3.7-rc1/arch/arm/mach-realview/hotplug.c linux/arch/arm/mach-realview/hotplug.c
--- linux-3.7-rc1/arch/arm/mach-realview/hotplug.c 2012-10-15 05:41:04.000000000 +0800
+++ linux/arch/arm/mach-realview/hotplug.c 2012-10-15 17:44:55.915942976 +0800
@@ -64,7 +64,7 @@
/*
* here's the WFI
*/
- asm(".word 0xe320f003\n"
+ asm(".inst 0xe320f003\n"
:
:
: "memory", "cc");
diff -urN linux-3.7-rc1/arch/arm/mach-shmobile/hotplug.c linux/arch/arm/mach-shmobile/hotplug.c
--- linux-3.7-rc1/arch/arm/mach-shmobile/hotplug.c 2012-10-15 05:41:04.000000000 +0800
+++ linux/arch/arm/mach-shmobile/hotplug.c 2012-10-15 17:45:20.509879863 +0800
@@ -39,7 +39,7 @@
/*
* here's the WFI
*/
- asm(".word 0xe320f003\n"
+ asm(".inst 0xe320f003\n"
:
:
: "memory", "cc");
Since ARM processor can be configured to work in BE-8 big-endian, I thinks this patch is necessary. Any suggestions is welcomed.
Thanks
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 at vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
^ permalink raw reply [flat|nested] 15+ 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 10:30 ` 答复: " Yangfei (Felix)
@ 2012-10-15 15:33 ` Fei Yang
1 sibling, 0 replies; 15+ 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, linux-kernel, 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] 15+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-15 15:33 ` Fei Yang
0 siblings, 0 replies; 15+ messages in thread
From: Fei Yang @ 2012-10-15 15:33 UTC (permalink / raw)
To: linux-arm-kernel
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 at 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] 15+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-15 15:33 ` Fei Yang
0 siblings, 0 replies; 15+ 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, linux-kernel, 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] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
2012-10-15 15:33 ` Fei Yang
(?)
@ 2012-10-16 12:49 ` Dave Martin
-1 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-16 12:49 ` Dave Martin
0 siblings, 0 replies; 15+ messages in thread
From: Dave Martin @ 2012-10-16 12:49 UTC (permalink / raw)
To: linux-arm-kernel
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 at 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 at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann
@ 2012-10-16 12:49 ` Dave Martin
0 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
2012-10-16 12:49 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Dave Martin
(?)
@ 2012-10-16 16:33 ` Fei Yang
-1 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-16 16:33 ` Fei Yang
0 siblings, 0 replies; 15+ messages in thread
From: Fei Yang @ 2012-10-16 16:33 UTC (permalink / raw)
To: linux-arm-kernel
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 at 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 at 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] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann
@ 2012-10-16 16:33 ` Fei Yang
0 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
2012-10-16 16:33 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Fei Yang
(?)
@ 2012-10-16 17:25 ` Dave Martin
-1 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
* [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness
@ 2012-10-16 17:25 ` Dave Martin
0 siblings, 0 replies; 15+ messages in thread
From: Dave Martin @ 2012-10-16 17:25 UTC (permalink / raw)
To: linux-arm-kernel
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 at 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 at 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] 15+ messages in thread
* Re: [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann
@ 2012-10-16 17:25 ` Dave Martin
0 siblings, 0 replies; 15+ 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, linux-hotplug, linux-kernel,
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] 15+ messages in thread
end of thread, other threads:[~2012-10-16 17:25 UTC | newest]
Thread overview: 15+ 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 10:30 ` 答复: " Yangfei (Felix)
2012-10-15 15:33 ` [PATCH] " Fei Yang
2012-10-15 15:33 ` Fei Yang
2012-10-15 15:33 ` Fei Yang
2012-10-16 12:49 ` Dave Martin
2012-10-16 12:49 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann Dave Martin
2012-10-16 12:49 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Dave Martin
2012-10-16 16:33 ` Fei Yang
2012-10-16 16:33 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann Fei Yang
2012-10-16 16:33 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Fei Yang
2012-10-16 17:25 ` Dave Martin
2012-10-16 17:25 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endiann Dave Martin
2012-10-16 17:25 ` [PATCH] Re: Hardcoded instruction causes certain features to fail on ARM platfrom due to endianness Dave Martin
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