2012/10/15 Mikael Pettersson <mikpe@xxxxxxxx>:
> 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.
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>
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");
--
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