[PATCH 0/4] Consistently enter the kernel in ARM state

[PATCH 0/4] Consistently enter the kernel in ARM state

[Dave Martin]

This series rationalises the kernel entry requirements so that
Image is entered in ARM state, just like zImage.

This should enable Image to be booted reliably for Thumb-2 kernels,
just like zImage.

The Booting documentation is updated to describe the requirement:
this resolves the ARM/Thumb ambiguity for Thumb-2 kernels; for ARM
kernels there is no implied change.

Dave Martin (4):
  ARM: head: Always Enter the kernel in ARM state
  ARM: head-nommu: Always enter the kernel in ARM state
  ARM: zImage: Jump to the decompressed kernel entry point in ARM state
  ARM: Documentation: clarify entry requirements for ARM versus Thumb-2

 Documentation/arm/Booting       |    5 +++++
 arch/arm/boot/compressed/head.S |    3 ++-
 arch/arm/kernel/head-nommu.S    |    8 ++++++++
 arch/arm/kernel/head.S          |    8 ++++++++
 4 files changed, 23 insertions(+), 1 deletions(-)

-- 
1.7.4.1

[PATCH 1/4] ARM: head: Always Enter the kernel in ARM state

[Dave Martin]

This makes Image directly bootable; otherwise the kernel is reliant
on the zImage decompressor to switch to the correct instruction
set.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
---
 arch/arm/kernel/head.S |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 278c1b0..742b610 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -71,8 +71,16 @@
  * crap here - that's what the boot loader (or in extreme, well justified
  * circumstances, zImage) is for.
  */
+	.arm
+
 	__HEAD
 ENTRY(stext)
+
+ THUMB(	adr	r9, BSYM(1f)	)	@ Kernel is always entered in ARM.
+ THUMB(	bx	r9		)	@ If this is a Thumb-2 kernel,
+ THUMB(	.thumb			)	@ switch to Thumb now.
+ THUMB(1:			)
+
 	setmode	PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
 						@ and irqs disabled
 	mrc	p15, 0, r9, c0, c0		@ get processor id
-- 
1.7.4.1

[PATCH 2/4] ARM: head-nommu: Always enter the kernel in ARM state

[Dave Martin]

This makes Image directly bootable; otherwise the kernel is reliant
on the zImage decompressor to switch to the correct instruction
set.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
---
 arch/arm/kernel/head-nommu.S |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index 6b1e0ad..d46f259 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -32,8 +32,16 @@
  * numbers for r1.
  *
  */
+	.arm
+
 	__HEAD
 ENTRY(stext)
+
+ THUMB(	adr	r9, BSYM(1f)	)	@ Kernel is always entered in ARM.
+ THUMB(	bx	r9		)	@ If this is a Thumb-2 kernel,
+ THUMB(	.thumb			)	@ switch to Thumb now.
+ THUMB(1:			)
+
 	setmode	PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
 						@ and irqs disabled
 #ifndef CONFIG_CPU_CP15
-- 
1.7.4.1

[PATCH 3/4] ARM: zImage: Jump to the decompressed kernel entry point in ARM state

[Dave Martin]

This change is required in order to enter the kernel correctly
now that the main kernel entry point expects to be called in
ARM state.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
---
 arch/arm/boot/compressed/head.S |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index f9da419..51af709 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -353,7 +353,8 @@ not_relocated:	mov	r0, #0
 		mov	r0, #0			@ must be zero
 		mov	r1, r7			@ restore architecture number
 		mov	r2, r8			@ restore atags pointer
-		mov	pc, r4			@ call kernel
+ ARM(		mov	pc, r4	)		@ call kernel
+ THUMB(		bx	r4	)		@ entry point is always ARM
 
 		.align	2
 		.type	LC0, #object
-- 
1.7.4.1

[PATCH 4/4] ARM: Documentation: clarify entry requirements for ARM versus Thumb-2

[Dave Martin]

Currently, the kernel entry requirements are not explicit about
whether the kernel should be entered in ARM or Thumb-2.

Now that the boot protocol consistently requires the kernel Image
or zImage to be entered in ARM state, document this requirement
explicitly.

A different rule will be needed for Cortex-M class CPUs as and when
support for these lands upstream, since these CPUs don't support
the ARM instruction set at all: a note is added to the effect that
the kernel must be entered in Thumb on such systems.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
---
 Documentation/arm/Booting |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting
index 4e686a2..a341d87 100644
--- a/Documentation/arm/Booting
+++ b/Documentation/arm/Booting
@@ -164,3 +164,8 @@ In either case, the following conditions must be met:
 - The boot loader is expected to call the kernel image by jumping
   directly to the first instruction of the kernel image.
 
+  On CPUs supporting the ARM instruction set, the entry must be
+  made in ARM state, even for a Thumb-2 kernel.
+
+  On CPUs supporting only the Thumb instruction set such as
+  Cortex-M class CPUs, the entry must be made in Thumb state.
-- 
1.7.4.1

[PATCH 0/4] Consistently enter the kernel in ARM state

[Nicolas Pitre]

On Mon, 20 Jun 2011, Dave Martin wrote:

> This series rationalises the kernel entry requirements so that
> Image is entered in ARM state, just like zImage.
> 
> This should enable Image to be booted reliably for Thumb-2 kernels,
> just like zImage.
> 
> The Booting documentation is updated to describe the requirement:
> this resolves the ARM/Thumb ambiguity for Thumb-2 kernels; for ARM
> kernels there is no implied change.
> 
> Dave Martin (4):
>   ARM: head: Always Enter the kernel in ARM state
>   ARM: head-nommu: Always enter the kernel in ARM state
>   ARM: zImage: Jump to the decompressed kernel entry point in ARM state

I'm afraid the above 3 patches will have to be folded together, 
otherwise a Thumb2 kernel won't boot if the last patch is not applied, 
which might cause problems with git bisect.

Otherwise you can add "Acked-by Nicolas Pitre <nicolas.pitre@linaro.org>"
to all of them.


Nicolas

[PATCH 0/4] Consistently enter the kernel in ARM state

[Dave Martin]

On Mon, Jun 20, 2011 at 10:01:11AM -0400, Nicolas Pitre wrote:
> On Mon, 20 Jun 2011, Dave Martin wrote:
> 
> > This series rationalises the kernel entry requirements so that
> > Image is entered in ARM state, just like zImage.
> > 
> > This should enable Image to be booted reliably for Thumb-2 kernels,
> > just like zImage.
> > 
> > The Booting documentation is updated to describe the requirement:
> > this resolves the ARM/Thumb ambiguity for Thumb-2 kernels; for ARM
> > kernels there is no implied change.
> > 
> > Dave Martin (4):
> >   ARM: head: Always Enter the kernel in ARM state
> >   ARM: head-nommu: Always enter the kernel in ARM state
> >   ARM: zImage: Jump to the decompressed kernel entry point in ARM state
> 
> I'm afraid the above 3 patches will have to be folded together, 
> otherwise a Thumb2 kernel won't boot if the last patch is not applied, 
> which might cause problems with git bisect.

Hmm, I was wondering about that.

> Otherwise you can add "Acked-by Nicolas Pitre <nicolas.pitre@linaro.org>"
> to all of them.

I'll fold the patches together.  It's a small series, so that shouldn't
cause trouble for people.

Thanks for the feedback.

Cheers
---Dave