[Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Joel Fernandes]

Loading kernel at offset 0x10000 works only for zImage, but not for Image,
because the kernel expect the start of decompressed kernel (.head.text) to be
at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
offset Qemu loads it at is 0x10000.

With zImage, this need is met because zImage loads the uncompressed Image
correctly, however when loading an Image and executing directly Qemu is
required it to load it at the correct location. Doing so, doesn't break Qemu's
zImage loading. With this patch, both zImage and Image work correctly.

Signed-off-by: Joel Fernandes <joelf@ti.com>
---
 hw/arm/boot.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index dc62918..566b5c2 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -23,7 +23,7 @@
  * They have different preferred image load offsets from system RAM base.
  */
 #define KERNEL_ARGS_ADDR 0x100
-#define KERNEL_LOAD_ADDR 0x00010000
+#define KERNEL_LOAD_ADDR 0x00008000
 #define KERNEL64_LOAD_ADDR 0x00080000
 
 typedef enum {
-- 
1.7.9.5

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Christopher Covington]

Hi Joel,

On 03/24/2014 11:34 PM, Joel Fernandes wrote:
> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
> because the kernel expect the start of decompressed kernel (.head.text) to be

Nit: expects

> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in

Nit: enforced

> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
> offset Qemu loads it at is 0x10000.
> 
> With zImage, this need is met because zImage loads the uncompressed Image
> correctly, however when loading an Image and executing directly Qemu is
> required it to load it at the correct location. Doing so, doesn't break Qemu's
> zImage loading. With this patch, both zImage and Image work correctly.

I had just been playing with my own version of this change. Glad to see it
going upstream.

Tested-by: Christopher Covington <cov@codeaurora.org>

Thanks,
Christopher

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by the Linux Foundation.

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Peter Maydell]

On 25 March 2014 03:34, Joel Fernandes <joelf@ti.com> wrote:
> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
> because the kernel expect the start of decompressed kernel (.head.text) to be
> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
> offset Qemu loads it at is 0x10000.
>
> With zImage, this need is met because zImage loads the uncompressed Image
> correctly, however when loading an Image and executing directly Qemu is
> required it to load it at the correct location. Doing so, doesn't break Qemu's
> zImage loading. With this patch, both zImage and Image work correctly.
>
> Signed-off-by: Joel Fernandes <joelf@ti.com>
> ---
>  hw/arm/boot.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index dc62918..566b5c2 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -23,7 +23,7 @@
>   * They have different preferred image load offsets from system RAM base.
>   */
>  #define KERNEL_ARGS_ADDR 0x100
> -#define KERNEL_LOAD_ADDR 0x00010000
> +#define KERNEL_LOAD_ADDR 0x00008000
>  #define KERNEL64_LOAD_ADDR 0x00080000

The patch and rationale seem plausible, but I'm a bit
reluctant to apply this this close to 2.0 release, because
QEMU has loaded images at this address for 8 years without
anybody complaining, and I worry that we might accidentally
break some other use case somehow.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Joel Fernandes]

On Tue, Mar 25, 2014 at 7:29 AM, Christopher Covington
<cov@codeaurora.org> wrote:
> Hi Joel,
>
> On 03/24/2014 11:34 PM, Joel Fernandes wrote:
>> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
>> because the kernel expect the start of decompressed kernel (.head.text) to be
>
> Nit: expects
>
>> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
>> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
>
> Nit: enforced
>
>> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
>> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
>> offset Qemu loads it at is 0x10000.
>>
>> With zImage, this need is met because zImage loads the uncompressed Image
>> correctly, however when loading an Image and executing directly Qemu is
>> required it to load it at the correct location. Doing so, doesn't break Qemu's
>> zImage loading. With this patch, both zImage and Image work correctly.
>
> I had just been playing with my own version of this change. Glad to see it
> going upstream.
>
> Tested-by: Christopher Covington <cov@codeaurora.org>
>

Thanks, I updated the patch with these changes.

-Joel

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Joel Fernandes]

On 03/25/2014 08:13 AM, Peter Maydell wrote:
> On 25 March 2014 03:34, Joel Fernandes <joelf@ti.com> wrote:
>> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
>> because the kernel expect the start of decompressed kernel (.head.text) to be
>> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
>> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
>> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
>> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
>> offset Qemu loads it at is 0x10000.
>>
>> With zImage, this need is met because zImage loads the uncompressed Image
>> correctly, however when loading an Image and executing directly Qemu is
>> required it to load it at the correct location. Doing so, doesn't break Qemu's
>> zImage loading. With this patch, both zImage and Image work correctly.
>>
>> Signed-off-by: Joel Fernandes <joelf@ti.com>
>> ---
>>  hw/arm/boot.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
>> index dc62918..566b5c2 100644
>> --- a/hw/arm/boot.c
>> +++ b/hw/arm/boot.c
>> @@ -23,7 +23,7 @@
>>   * They have different preferred image load offsets from system RAM base.
>>   */
>>  #define KERNEL_ARGS_ADDR 0x100
>> -#define KERNEL_LOAD_ADDR 0x00010000
>> +#define KERNEL_LOAD_ADDR 0x00008000
>>  #define KERNEL64_LOAD_ADDR 0x00080000
> 
> The patch and rationale seem plausible, but I'm a bit
> reluctant to apply this this close to 2.0 release, because
> QEMU has loaded images at this address for 8 years without
> anybody complaining, and I worry that we might accidentally
> break some other use case somehow.

I understand.
FWIW, I also tested with a15-vexpress and zImage.

thanks,

-Joel

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Peter Maydell]

On 25 March 2014 03:34, Joel Fernandes <joelf@ti.com> wrote:
> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
> because the kernel expect the start of decompressed kernel (.head.text) to be
> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
> offset Qemu loads it at is 0x10000.
>
> With zImage, this need is met because zImage loads the uncompressed Image
> correctly, however when loading an Image and executing directly Qemu is
> required it to load it at the correct location. Doing so, doesn't break Qemu's
> zImage loading. With this patch, both zImage and Image work correctly.
>
> Signed-off-by: Joel Fernandes <joelf@ti.com>

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

I'll put this in target-arm.next after 2.0 has released.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Peter Crosthwaite]

On Wed, Apr 2, 2014 at 3:10 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 25 March 2014 03:34, Joel Fernandes <joelf@ti.com> wrote:
>> Loading kernel at offset 0x10000 works only for zImage, but not for Image,
>> because the kernel expect the start of decompressed kernel (.head.text) to be
>> at an address that's a distance that's 16MB aligned from  PAGE_OFFSET +
>> TEXT_OFFSET (see vmlinux.lds.S). This check is enfornced in __fixup_pv_table in
>> arch/arm/kernel/head.S TEXT_OFFSET is 0x00008000, so a 16MB alignment needs to
>> have a "0x8000" in the lower 16 bits so that they cancel out. Currently the
>> offset Qemu loads it at is 0x10000.
>>
>> With zImage, this need is met because zImage loads the uncompressed Image
>> correctly, however when loading an Image and executing directly Qemu is
>> required it to load it at the correct location. Doing so, doesn't break Qemu's
>> zImage loading. With this patch, both zImage and Image work correctly.
>>
>> Signed-off-by: Joel Fernandes <joelf@ti.com>
>
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>

Like others, I have been carrying this change locally. Good to see it up!

Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Tested-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>

> I'll put this in target-arm.next after 2.0 has released.
>
> thanks
> -- PMM
>

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Peter Maydell]

On 2 April 2014 13:11, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
> Like others, I have been carrying this change locally. Good to see it up!

Why are you all booting raw Images anyway (just out of curiosity)? All my
test cases boot either a zImage or a uImage, or occasionally a full SD card
image, or I'd have noticed this earlier...

thanks
-- PMM

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Peter Crosthwaite]

On Wed, Apr 2, 2014 at 10:47 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 2 April 2014 13:11, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
>> Like others, I have been carrying this change locally. Good to see it up!
>
> Why are you all booting raw Images anyway (just out of curiosity)? All my
> test cases boot either a zImage or a uImage, or occasionally a full SD card
> image, or I'd have noticed this earlier...
>

Simplicity more than anything. It is much easier to debug against
head.S (esp. with the -d in_asm option), when you can see the head.s
asm as the very first thing the CPU executes. Otherwise you gotta
filter out the zImage stuffs. There have also been occasions where I
have broken QEMU locally as part of some random work-in-progress
development such that the zImage head doesnt work and i'd rather just
move my debug efforts to kernel proper. None of them are fantastic
reasons from a user perspective but it's just a little easier on
developing.

Regards,
Peter

> thanks
> -- PMM
>

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Christopher Covington]

[On 04/02/2014 08:47 AM, Peter Maydell wrote:
> On 2 April 2014 13:11, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
>> Like others, I have been carrying this change locally. Good to see it up!
> 
> Why are you all booting raw Images anyway (just out of curiosity)? All my
> test cases boot either a zImage or a uImage, or occasionally a full SD card
> image, or I'd have noticed this earlier...

I do it in part for uniformity with arm64 kernels.

Christopher

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by the Linux Foundation.

Re: [Qemu-devel] [PATCH] QEMU: ARM: boot: Load kernel at an Image friendly address

[Joel Fernandes]

On Wed, Apr 2, 2014 at 7:47 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 2 April 2014 13:11, Peter Crosthwaite <peter.crosthwaite@xilinx.com> wrote:
>> Like others, I have been carrying this change locally. Good to see it up!
>
> Why are you all booting raw Images anyway (just out of curiosity)? All my
> test cases boot either a zImage or a uImage, or occasionally a full SD card
> image, or I'd have noticed this earlier...

zImage fails for me on OMAP1, which I'm debugging, the errors have
more to do with writing out of memory limits. But I was not sure if
the problem was with decompression or something else, so I wanted to
boot the basic case (Image) first.

Thanks,
-Joel