Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Daniel Thompson 
On 17/04/14 21:35, Jason Gunthorpe wrote:
 The above is useful for loading the raw uncompressed Image without 
 carrying the full ELF baggage.

 What exactly is the full ELF baggage? Aren't there existing mechanisms to 
 omit
 debugging symbols, for example, if size is of concern?
 
 FWIW, it is a small non-intrusive change to produce ELFs with the
 proper LMA, if it is useful for specialized tooling, here is the 3.14
 version of the patch I created (I see it needs a bit of cleanup..)
 You must also force PATCH_PHYS_VIRT off.
 
 The ELF also has the correct entry point address, so ELF tooling can
 just jump into it, after setting the proper register values according
 to the boot protocol.

That might be a useful approach for single platform kernels but I don't
think such an approach can work for multi-arch kernels since, because
the RAM can be located anywhere in the address map, the physical load
address is platform dependant.


Daniel.

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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Daniel Thompson 
On 22/04/14 11:40, Russell King - ARM Linux wrote:
 On Tue, Apr 22, 2014 at 11:26:53AM +0100, Daniel Thompson wrote:
 On 18/04/14 05:34, Nicolas Pitre wrote:
 I'm not suggesting to break anything or changing existing platforms,
 but how do we improve the Image format in a compatible way. If
 bootloaders want to support booting Image files or vmlinux directly,
 then we should support that including any compatible changes to make
 things work better.
 And why would bootloaders want that?  Just to create confusion with 
 the established boot protocol?

 I'd say that they don't. My original concern was how the different
 architectures negotiate if more than one arch wants a special text
 offset, not how to write a correct bootloader.

 The existing uImage files already provide sufficient information to load
 the kernel regardless of the TEXT_OFFSET chosen by negotiation among the
 enabled architectures.
 
 No.  uImage merely specifies the address at which to load/execute the
 zImage, and more often than not this is a step which has to be done
 after kernel build as the kernel build does not have the information
 to be able to generate a uImage on its own.  Also, a uImage generated
 for one platform will not necessarily boot on a different platform
 even though the contents of the uImage may be 100% identical apart
 from the header.

You were right about the typo but I'm afraid the location was much
earlier. Sorry! Replace uImage with the vmlinux ELF image and my last
post is not quite such nonsense.


 The entry point is PAGE_OFFSET + TEXT_OFFSET and, although only
 implicitly defined, the entry point cannot be set to any other value
 without making a backward incompatible to arm/Booting:
 The boot loader is expected to call the kernel image by jumping
 directly to the first instruction of the kernel image.

Although for this bit probably will always be nonsense.


 Therefore providing PAGE_OFFSET remains 1G aligned and the hardware
 meets the not-unreasonably-stupid test (i.e. TEXT_OFFSET  1G) then
 deriving the right value for TEXT_OFFSET is a trivial mask operation on
 the entry point.
 
 PAGE_OFFSET doesn't have to be 1G aligned.  As I've already pointed out
 in previous replies, PAGE_OFFSET is totally irrelevant in this discussion.
 PAGE_OFFSET is the *virtual* address of the RAM, and has no bearing what
 so ever on where you load the kernel image.

When trying to directly load an ELF image, where by default vaddr ==
paddr, its actually PAGE_OFFSET we're looking for. Combining that with
some platform specific knowledge about RAM (i.e. typical PHYS_OFFSET for
the platform) and we can derive sensible paddr values.

At the start of last week the loader I used assumed TEXT_OFFSET would be
0x8000 and used it to calculate PAGE_OFFSET from the ELF entry point.

So I guess what I have now is still broken just, not quite as obviously...
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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Michal Simek 
On 04/17/2014 10:35 PM, Jason Gunthorpe wrote:
 On Thu, Apr 17, 2014 at 02:33:43PM -0400, Christopher Covington wrote:
 On 04/16/2014 07:21 PM, Nicolas Pitre wrote:
 On Wed, 16 Apr 2014, Christopher Covington wrote:

 Thank you for the suggestion. This approach also came to mind, but it would
 require new documentation and tooling in the JTAG scripts or simulator
 equivalent. That's another aspect of the ELF-based approaches that I
 like--hopefully existing documentation and tool support could be reused.

 The above is useful for loading the raw uncompressed Image without 
 carrying the full ELF baggage.

 What exactly is the full ELF baggage? Aren't there existing mechanisms to 
 omit
 debugging symbols, for example, if size is of concern?
 
 FWIW, it is a small non-intrusive change to produce ELFs with the
 proper LMA, if it is useful for specialized tooling, here is the 3.14
 version of the patch I created (I see it needs a bit of cleanup..)
 You must also force PATCH_PHYS_VIRT off.
 
 The ELF also has the correct entry point address, so ELF tooling can
 just jump into it, after setting the proper register values according
 to the boot protocol.
 
 From ca9763668eed2eaaf0c0c2640f1502c22b68a739 Mon Sep 17 00:00:00 2001
 From: Jason Gunthorpe jguntho...@obsidianresearch.com
 Date: Fri, 14 Sep 2012 11:27:17 -0600
 Subject: [PATCH] [ARM] Use AT() in the linker script to create correct program
  headers
 
 The standard linux asm-generic/vmlinux.lds.h already supports this,
 and it seems other architectures do as well.
 
 The goal is to create an ELF file that has correct program headers. We
 want to see the VirtAddr be the runtime address of the kernel with the
 MMU turned on, and PhysAddr be the physical load address for the section
 with no MMU.
 
 This allows ELF based boot loaders to properly load vmlinux:
 
 $ readelf -l vmlinux
 Entry point 0x8000
   Type   Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
   LOAD   0x008000 0xc0008000 0x8000 0x372244 0x3a4310 RWE 0x8000
 
 Signed-off-by: Jason Gunthorpe jguntho...@obsidianresearch.com
 ---
  arch/arm/include/asm/memory.h |  2 +-
  arch/arm/kernel/vmlinux.lds.S | 51 
 +--
  2 files changed, 31 insertions(+), 22 deletions(-)
 
 diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
 index 8756e4b..551e971 100644
 --- a/arch/arm/include/asm/memory.h
 +++ b/arch/arm/include/asm/memory.h
 @@ -350,7 +350,7 @@ static inline __deprecated void *bus_to_virt(unsigned 
 long x)
  #define virt_addr_valid(kaddr)   (((unsigned long)(kaddr) = PAGE_OFFSET 
  (unsigned long)(kaddr)  (unsigned long)high_memory) \
pfn_valid(__pa(kaddr)  PAGE_SHIFT) 
 )
  
 -#endif
 +#endif /* __ASSEMBLY__ */


This is unrelated change.

  
  #include asm-generic/memory_model.h
  
 diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
 index 7bcee5c..15353d2 100644
 --- a/arch/arm/kernel/vmlinux.lds.S
 +++ b/arch/arm/kernel/vmlinux.lds.S
 @@ -3,6 +3,13 @@
   * Written by Martin Mares m...@atrey.karlin.mff.cuni.cz
   */
  
 +/* If we have a known, fixed physical load address then set LOAD_OFFSET
 +   and generate an ELF that has the physical load address in the program
 +   headers. */
 +#ifndef CONFIG_ARM_PATCH_PHYS_VIRT
 +#define LOAD_OFFSET (PAGE_OFFSET - PLAT_PHYS_OFFSET)
 +#endif
 +
  #include asm-generic/vmlinux.lds.h
  #include asm/cache.h
  #include asm/thread_info.h
 @@ -43,7 +50,7 @@
  #endif
  
  OUTPUT_ARCH(arm)
 -ENTRY(stext)
 +ENTRY(phys_start)
  
  #ifndef __ARMEB__
  jiffies = jiffies_64;
 @@ -86,11 +93,13 @@ SECTIONS
  #else
   . = PAGE_OFFSET + TEXT_OFFSET;
  #endif
 - .head.text : {
 + .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {
   _text = .;
 + phys_start = . - LOAD_OFFSET;
   HEAD_TEXT
   }

I am not quite about these changes above but Russell can comment it.

 - .text : {   /* Real text segment*/
 + /* Real text segment */
 + .text :  AT(ADDR(.text) - LOAD_OFFSET) {

The rest is just fine. It is exactly what I have written some months
ago when I want to get ELF with correct addresses for qemu.
It is the same what it is written in asm-generic/vmlinux.lds.h
and ARM should also use it.

Thanks,
Michal

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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Jason Gunthorpe 
  index 8756e4b..551e971 100644
  +++ b/arch/arm/include/asm/memory.h
  @@ -350,7 +350,7 @@ static inline __deprecated void *bus_to_virt(unsigned 
  long x)
   #define virt_addr_valid(kaddr) (((unsigned long)(kaddr) = PAGE_OFFSET 
   (unsigned long)(kaddr)  (unsigned long)high_memory) \
   pfn_valid(__pa(kaddr)  PAGE_SHIFT) 
  )
   
  -#endif
  +#endif /* __ASSEMBLY__ */

 This is unrelated change.

Right, as I said it needs some cleanup :) This is left overs from
rebasing to 3.14 - the original had to carry some small changes to
memory.h as well, but now that we have PLAT_PHYS_OFFSET that isn't
necessary.
 
  @@ -43,7 +50,7 @@
   #endif
   
   OUTPUT_ARCH(arm)
  -ENTRY(stext)
  +ENTRY(phys_start)
   
   #ifndef __ARMEB__
   jiffies = jiffies_64;
  @@ -86,11 +93,13 @@ SECTIONS
   #else
  . = PAGE_OFFSET + TEXT_OFFSET;
   #endif
  -   .head.text : {
  +   .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {
  _text = .;
  +   phys_start = . - LOAD_OFFSET;
  HEAD_TEXT
  }
 
 I am not quite about these changes above but Russell can comment it.

This is adjusting the entry point address in the ELF.

I have copied what other arch's are doing and used the physical
address as the entry address (see x86, ia64).

Jason
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Jason Gunthorpe 
On Tue, Apr 22, 2014 at 10:44:14AM +0100, Daniel Thompson wrote:
 On 17/04/14 21:35, Jason Gunthorpe wrote:
  The above is useful for loading the raw uncompressed Image without 
  carrying the full ELF baggage.
 
  What exactly is the full ELF baggage? Aren't there existing mechanisms to 
  omit
  debugging symbols, for example, if size is of concern?
  
  FWIW, it is a small non-intrusive change to produce ELFs with the
  proper LMA, if it is useful for specialized tooling, here is the 3.14
  version of the patch I created (I see it needs a bit of cleanup..)
  You must also force PATCH_PHYS_VIRT off.
  
  The ELF also has the correct entry point address, so ELF tooling can
  just jump into it, after setting the proper register values according
  to the boot protocol.
 
 That might be a useful approach for single platform kernels but I don't
 think such an approach can work for multi-arch kernels since, because
 the RAM can be located anywhere in the address map, the physical load
 address is platform dependant.

Right, I think everyone realizes that.

What this patch does is make kernels that are built with
PLAT_PHYS_OFFSET set and CONFIG_ARM_PATCH_PHYS_VIRT disabled produce
an ELF that reflects the build configuration.

Based on comments from others in the thread this is looking useful for
a variety of cases.

I'm not sure who would need to ack this patch? I can clean it up of course.

Thanks,
Jason
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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Russell King - ARM Linux 
On Tue, Apr 22, 2014 at 04:50:12PM +0200, Michal Simek wrote:
 On 04/17/2014 10:35 PM, Jason Gunthorpe wrote:
  +/* If we have a known, fixed physical load address then set LOAD_OFFSET
  +   and generate an ELF that has the physical load address in the program
  +   headers. */
  +#ifndef CONFIG_ARM_PATCH_PHYS_VIRT
  +#define LOAD_OFFSET (PAGE_OFFSET - PLAT_PHYS_OFFSET)
  +#endif
  +
...
  -   .head.text : {
  +   .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {
  _text = .;
  +   phys_start = . - LOAD_OFFSET;
  HEAD_TEXT
  }
 
 I am not quite about these changes above but Russell can comment it.

I don't think /anyone/ is seriously proposing that we should merge this
patch... because that won't happen.  It should be clear enough from the
discussion why that is, but in case it isn't, take a look above.

What is that ifdef saying.  It's saying that if you enable
ARM_PATCH_PHYS_VIRT, which is an absolute requirement for multi-
platform kernels, then you get the proper LMA addresses.  If you don't,
then you don't get proper LMA addresses.

Put another way, if your platform is part of the multi-platform kernel
then you are *excluded* from being able to use this... unless you hack
the Kconfig, and then also provide a constant value for PHYS_OFFSET,
thereby _tying_ the kernel you built to a _single_ platform.

You can't do this _and_ have a multi-platform kernel.

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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Jason Gunthorpe 
On Tue, Apr 22, 2014 at 06:11:42PM +0100, Russell King - ARM Linux wrote:

 Put another way, if your platform is part of the multi-platform kernel
 then you are *excluded* from being able to use this... unless you hack
 the Kconfig, and then also provide a constant value for PHYS_OFFSET,
 thereby _tying_ the kernel you built to a _single_ platform.

That is exactly right. To get a fixed LMA you must commit to a
non-relocatable kernel image.

Realistically this patch would need to be accompanied by something
that makes ARM_PATCH_PHYS_VIRT optional for multiplatform based on
EXPERT or similar.

The best usecase seems to be to support ELF tooling for low level
debugging activities, a non-relocatable image isn't a blocker for that
case.

Since the patch is a no-op if LOAD_OFFSET isn't set, is there a
downside I don't see?

Thanks,
Jason
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Nicolas Pitre 
On Tue, 22 Apr 2014, Jason Gunthorpe wrote:

 On Tue, Apr 22, 2014 at 10:44:14AM +0100, Daniel Thompson wrote:
  On 17/04/14 21:35, Jason Gunthorpe wrote:
   The above is useful for loading the raw uncompressed Image without 
   carrying the full ELF baggage.
  
   What exactly is the full ELF baggage? Aren't there existing mechanisms 
   to omit
   debugging symbols, for example, if size is of concern?
   
   FWIW, it is a small non-intrusive change to produce ELFs with the
   proper LMA, if it is useful for specialized tooling, here is the 3.14
   version of the patch I created (I see it needs a bit of cleanup..)
   You must also force PATCH_PHYS_VIRT off.
   
   The ELF also has the correct entry point address, so ELF tooling can
   just jump into it, after setting the proper register values according
   to the boot protocol.
  
  That might be a useful approach for single platform kernels but I don't
  think such an approach can work for multi-arch kernels since, because
  the RAM can be located anywhere in the address map, the physical load
  address is platform dependant.
 
 Right, I think everyone realizes that.
 
 What this patch does is make kernels that are built with
 PLAT_PHYS_OFFSET set and CONFIG_ARM_PATCH_PHYS_VIRT disabled produce
 an ELF that reflects the build configuration.
 
 Based on comments from others in the thread this is looking useful for
 a variety of cases.

Well...

We do not want people in general to have PLAT_PHYS_OFFSET defined and
CONFIG_ARM_PATCH_PHYS_VIRT disabled.  In fact a huge effort has been 
deployed to go the exact opposite way over the last few years.

There are special cases where CONFIG_ARM_PATCH_PHYS_VIRT needs to be 
turned off for example.  But those are specialized configurations and 
they should be the exception not the norm.  And you should be knowing 
what you're doing in those cases.

So I doubt it is worth complexifying the linker script for something 
that is meant to be the exception, _especially_ if this is for some 
debugging environment purposes.  You may just adjust some setting in 
your environment or do a quick kernel modification locally instead.  
And if you don't know what to modify then you're probably lacking the 
necessary qualifications to perform that kind of kernel debugging in the 
first place.

Making the patch available on a mailing list is fine.  If it is useful 
to someone else then it'll be found.  But I don't think this is useful 
upstream.


Nicolas
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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Russell King - ARM Linux 
On Tue, Apr 22, 2014 at 11:53:25AM -0600, Jason Gunthorpe wrote:
 On Tue, Apr 22, 2014 at 06:11:42PM +0100, Russell King - ARM Linux wrote:
 
  Put another way, if your platform is part of the multi-platform kernel
  then you are *excluded* from being able to use this... unless you hack
  the Kconfig, and then also provide a constant value for PHYS_OFFSET,
  thereby _tying_ the kernel you built to a _single_ platform.
 
 That is exactly right. To get a fixed LMA you must commit to a
 non-relocatable kernel image.
 
 Realistically this patch would need to be accompanied by something
 that makes ARM_PATCH_PHYS_VIRT optional for multiplatform based on
 EXPERT or similar.
 
 The best usecase seems to be to support ELF tooling for low level
 debugging activities, a non-relocatable image isn't a blocker for that
 case.

Let's not forget that if you want to debug, it's because you've hit a
problem in the kernel you're running.  To get an ELF image you can debug,
you have to turn ARM_PATCH_PHYS_VIRT off, which changes the generated
code - which can in itself cause bugs to hide themselves.

Unfortunately, those kinds of bugs are not as rare as you might think.

 Since the patch is a no-op if LOAD_OFFSET isn't set, is there a
 downside I don't see?

It leads people into thinking that we support booting an ELF file.
We don't.

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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Russell King - ARM Linux 
On Tue, Apr 22, 2014 at 01:55:16PM -0400, Nicolas Pitre wrote:
 We do not want people in general to have PLAT_PHYS_OFFSET defined and
 CONFIG_ARM_PATCH_PHYS_VIRT disabled.  In fact a huge effort has been 
 deployed to go the exact opposite way over the last few years.
 
 There are special cases where CONFIG_ARM_PATCH_PHYS_VIRT needs to be 
 turned off for example.  But those are specialized configurations and 
 they should be the exception not the norm.  And you should be knowing 
 what you're doing in those cases.
 
 So I doubt it is worth complexifying the linker script for something 
 that is meant to be the exception, _especially_ if this is for some 
 debugging environment purposes.  You may just adjust some setting in 
 your environment or do a quick kernel modification locally instead.  
 And if you don't know what to modify then you're probably lacking the 
 necessary qualifications to perform that kind of kernel debugging in the 
 first place.
 
 Making the patch available on a mailing list is fine.  If it is useful 
 to someone else then it'll be found.  But I don't think this is useful 
 upstream.

Also, let's not forget that it the ELF file can be modified after the
kernel build:

$ vmlinux=your-vmlinux-file
$ newlma=lma-for-your-platform
$ arm-linux-objcopy $(
  arm-linux-objdump -h ${vmlinux} |
  grep -B1 'LOAD' | \
  sed -nr 's/^[ 0-9]*[0-9] ([^ ]*).*/--change-section-lma \1+${newlma}/p') \
  ${vmlinux} ${vmlinux}-${newlma}

(It would be nice if objcopy could be told change any section with _this_
attribute.)

The nice thing about this is that you can keep ARM_PATCH_PHYS_VIRT enabled
and not have to change the code in any way - you just fix up the headers on
the ELF file.

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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Russell King - ARM Linux 
On Tue, Apr 22, 2014 at 08:32:10PM +0200, Arnd Bergmann wrote:
 @@ -1943,6 +1953,7 @@ config DEPRECATED_PARAM_STRUCT
  # TEXT and BSS so we preserve their values in the config files.
  config ZBOOT_ROM_TEXT
   hex Compressed ROM boot loader base address
 + depends on BROKEN_MULTIPLATFORM
   default 0
   help
 The physical address at which the ROM-able zImage is to be
 @@ -1954,6 +1965,7 @@ config ZBOOT_ROM_TEXT
  
  config ZBOOT_ROM_BSS
   hex Compressed ROM boot loader BSS address
 + depends on BROKEN_MULTIPLATFORM
   default 0
   help
 The base address of an area of read/write memory in the target

Please get rid of the above changes.

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Re: [Qemu-devel] Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-22 Thread Arnd Bergmann 
On Tuesday 22 April 2014 19:38:55 Russell King - ARM Linux wrote:
 On Tue, Apr 22, 2014 at 08:32:10PM +0200, Arnd Bergmann wrote:
  @@ -1943,6 +1953,7 @@ config DEPRECATED_PARAM_STRUCT
   # TEXT and BSS so we preserve their values in the config files.
   config ZBOOT_ROM_TEXT
hex Compressed ROM boot loader base address
  + depends on BROKEN_MULTIPLATFORM
default 0
help
  The physical address at which the ROM-able zImage is to be
  @@ -1954,6 +1965,7 @@ config ZBOOT_ROM_TEXT
   
   config ZBOOT_ROM_BSS
hex Compressed ROM boot loader BSS address
  + depends on BROKEN_MULTIPLATFORM
default 0
help
  The base address of an area of read/write memory in the target
 
 Please get rid of the above changes.

Good point, fixed now.

Arnd
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-17 Thread Rob Herring 
On Wed, Apr 16, 2014 at 2:14 PM, Nicolas Pitre nicolas.pi...@linaro.org wrote:
 On Wed, 16 Apr 2014, Christopher Covington wrote:

 On 04/15/2014 06:44 AM, Daniel Thompson wrote:
  Hi Folks

[snip]

 Or could we patch up the linker script to set zero-based ELF load
 memory addresses (LMAs) [4] so that the physical addresses are almost right,
 you just might have to add a system-specific RAM offset, perhaps pulled out 
 of
 the device tree? If that won't work, we could generate some kind of
 vmlinux-phys with physical addresses. The latter two options might also
 simplify external debugging before __turn_mmu_on(). I like the sound of the
 LMA approach best, assuming it doesn't break existing stuff (I notice a few 
 AT
 directives in vmlinux.lds.S). Some of this might transfer to arm64 as well.
 What do you all think?

 If you really really want to get at the TEXT_OFFSET value in the
 uncompressed image, the simplest way would be:

 diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
 index f8c08839ed..de84d0635a 100644
 --- a/arch/arm/kernel/head.S
 +++ b/arch/arm/kernel/head.S
 @@ -78,6 +78,11 @@

 __HEAD
  ENTRY(stext)
 +
 +   b   1f
 +   .word   TEXT_OFFSET @ located at a 4-byte offset in Image
 +1:
 +
   ARM_BE8(setendbe )@ ensure we are in BE8 mode

   THUMB(adr r9, BSYM(1f))   @ Kernel is always entered in 
 ARM.

 This way the first word for Image would always be 0xea00 and the
 second one would be TEXT_OFFSET.  No other kernel Image binaries ever
 had 0xea00 as their first word so that also let you validate whether
 or not the TEXT_OFFSET value is there.

Better yet, we should adopt the arm64 Image header which has this and
other fields for arm Image files. We're going to have to deal with raw
Image (and Image.gz) in bootloaders for arm64, so we might as well
align things.

Rob
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-17 Thread Jason Gunthorpe 
On Thu, Apr 17, 2014 at 02:33:43PM -0400, Christopher Covington wrote:
 On 04/16/2014 07:21 PM, Nicolas Pitre wrote:
  On Wed, 16 Apr 2014, Christopher Covington wrote:
 
  Thank you for the suggestion. This approach also came to mind, but it would
  require new documentation and tooling in the JTAG scripts or simulator
  equivalent. That's another aspect of the ELF-based approaches that I
  like--hopefully existing documentation and tool support could be reused.
  
  The above is useful for loading the raw uncompressed Image without 
  carrying the full ELF baggage.
 
 What exactly is the full ELF baggage? Aren't there existing mechanisms to omit
 debugging symbols, for example, if size is of concern?

FWIW, it is a small non-intrusive change to produce ELFs with the
proper LMA, if it is useful for specialized tooling, here is the 3.14
version of the patch I created (I see it needs a bit of cleanup..)
You must also force PATCH_PHYS_VIRT off.

The ELF also has the correct entry point address, so ELF tooling can
just jump into it, after setting the proper register values according
to the boot protocol.

From ca9763668eed2eaaf0c0c2640f1502c22b68a739 Mon Sep 17 00:00:00 2001
From: Jason Gunthorpe jguntho...@obsidianresearch.com
Date: Fri, 14 Sep 2012 11:27:17 -0600
Subject: [PATCH] [ARM] Use AT() in the linker script to create correct program
 headers

The standard linux asm-generic/vmlinux.lds.h already supports this,
and it seems other architectures do as well.

The goal is to create an ELF file that has correct program headers. We
want to see the VirtAddr be the runtime address of the kernel with the
MMU turned on, and PhysAddr be the physical load address for the section
with no MMU.

This allows ELF based boot loaders to properly load vmlinux:

$ readelf -l vmlinux
Entry point 0x8000
  Type   Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD   0x008000 0xc0008000 0x8000 0x372244 0x3a4310 RWE 0x8000

Signed-off-by: Jason Gunthorpe jguntho...@obsidianresearch.com
---
 arch/arm/include/asm/memory.h |  2 +-
 arch/arm/kernel/vmlinux.lds.S | 51 +--
 2 files changed, 31 insertions(+), 22 deletions(-)

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 8756e4b..551e971 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -350,7 +350,7 @@ static inline __deprecated void *bus_to_virt(unsigned long 
x)
 #define virt_addr_valid(kaddr) (((unsigned long)(kaddr) = PAGE_OFFSET  
(unsigned long)(kaddr)  (unsigned long)high_memory) \
 pfn_valid(__pa(kaddr)  PAGE_SHIFT) 
)
 
-#endif
+#endif /* __ASSEMBLY__ */
 
 #include asm-generic/memory_model.h
 
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 7bcee5c..15353d2 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -3,6 +3,13 @@
  * Written by Martin Mares m...@atrey.karlin.mff.cuni.cz
  */
 
+/* If we have a known, fixed physical load address then set LOAD_OFFSET
+   and generate an ELF that has the physical load address in the program
+   headers. */
+#ifndef CONFIG_ARM_PATCH_PHYS_VIRT
+#define LOAD_OFFSET (PAGE_OFFSET - PLAT_PHYS_OFFSET)
+#endif
+
 #include asm-generic/vmlinux.lds.h
 #include asm/cache.h
 #include asm/thread_info.h
@@ -43,7 +50,7 @@
 #endif
 
 OUTPUT_ARCH(arm)
-ENTRY(stext)
+ENTRY(phys_start)
 
 #ifndef __ARMEB__
 jiffies = jiffies_64;
@@ -86,11 +93,13 @@ SECTIONS
 #else
. = PAGE_OFFSET + TEXT_OFFSET;
 #endif
-   .head.text : {
+   .head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {
_text = .;
+   phys_start = . - LOAD_OFFSET;
HEAD_TEXT
}
-   .text : {   /* Real text segment*/
+   /* Real text segment */
+   .text :  AT(ADDR(.text) - LOAD_OFFSET) {
_stext = .; /* Text and read-only data  */
__exception_text_start = .;
*(.exception.text)
@@ -128,12 +137,12 @@ SECTIONS
 * Stack unwinding tables
 */
. = ALIGN(8);
-   .ARM.unwind_idx : {
+   .ARM.unwind_idx : AT(ADDR(.ARM.unwind_idx) - LOAD_OFFSET) {
__start_unwind_idx = .;
*(.ARM.exidx*)
__stop_unwind_idx = .;
}
-   .ARM.unwind_tab : {
+   .ARM.unwind_tab : AT(ADDR(.ARM.unwind_tab) - LOAD_OFFSET) {
__start_unwind_tab = .;
*(.ARM.extab*)
__stop_unwind_tab = .;
@@ -153,49 +162,49 @@ SECTIONS
 * only thing that matters is their relative offsets
 */
__vectors_start = .;
-   .vectors 0 : AT(__vectors_start) {
+   .vectors 0 : AT(__vectors_start - LOAD_OFFSET) {
*(.vectors)
}
. = __vectors_start + SIZEOF(.vectors);
__vectors_end = .;
 
__stubs_start = .;
-   .stubs

Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-17 Thread Rob Herring 
On Thu, Apr 17, 2014 at 4:35 PM, Russell King - ARM Linux
li...@arm.linux.org.uk wrote:
 On Thu, Apr 17, 2014 at 04:18:45PM -0500, Rob Herring wrote:
 The problem here is more than just the TEXT_OFFSET changed. From what
 I've heard, there are some QC chips which need much more reserved RAM
 than the 2MB discussed here. Changing the TEXT_OFFSET is a hack that
 doesn't scale.

 You may think it's a hack, but we really can't get around this.  There
 really are platforms out there where we must do this kind of stuff.  I
 invite you next time you meet up to talk to Michal Simek.  There's no
 way they can load the kernel at 32K into RAM.

In fact, I have discussed this with him. If we're having discussions
about it, then obviously some problems remain.

 A simple issue is you are now wasting 2MB of low memory on every
 platform. Not such a big deal I guess. But what if more is needed?

 Why do you think it's wasted in the general case?  Do you think the
 first 16K is ignored by Linux?  All memory will be freed to the Linux
 page allocator unless it has an explicit reservation in memblock.  So
 the 2MB won't be wasted - it will be freed as before to the page
 allocator.

Okay, my mistake.

 The zImage requires that the kernel be placed at a 128M aligned
 address plus TEXT_OFFSET. The v2p patching then requires the kernel to
 be located within the first 16MB of RAM. So the Image can only ever be
 placed at 0x8000 - 15.?MB from a 128MB aligned address. You can never
 have the first 16-127MB of RAM reserved.

 Wrong.  You can have as much RAM as you want reserved, you just can't
 manage it with Linux memory allocators if you go over 16MB.

 Remember that the virtual address space PAGE_OFFSET...kernel corresponds
 with PHYS_OFFSET...kernel.  So, if you have 16MB between PHYS_OFFSET and
 the kernel, then you have 16MB between PAGE_OFFSET and the kernel.  Your
 modules are looking very distant, and PCREL24 relocations become
 troublesome.

For the reasons you give here, doesn't that mean you want to have
TEXT_OFFSET be as small as possible? And (ab)using TEXT_OFFSET to
reserve 16, 32, 64MB, etc, would be a bad idea. Also, that only gives
us a compile time memory reservation.

Here's a simple test of what I was trying to point out. I took a
working kernel with TEXT_OFFSET of 0x8000 and booted it on QEMU using
the virt machine which RAM normally starts at 0x4000. Then
varying the RAM base, I get these results:

0x4000 - boots
0x4100 - no output because the decompressor will still put the
Image at 0x40008000.
0x4800 - boots

So without changing TEXT_OFFSET, you can only vary the PHYS_OFFSET in
128MB steps. For anything in between you have to use TEXT_OFFSET. Is
that really the right solution?

BTW, a TEXT_OFFSET of 0x408000 or more doesn't work either due to the
limits in immediate values, but that problem could be easily fixed.

 The only way to have reserved
 memory (in chucks of 16MB) is by loading an Image file directly
 instead. The bootloaders will know the start of RAM and any reserved
 memory size because they can simply parse DT.

 Bootloaders are going to have to change for arm64 Image support
 anyway, so we should have an aligned solution here.

 No.  You simply can't eliminate any of the above - each one has been
 negotiated through quite an amount of discussion with relevant parties
 and/or due to technical requirements and they just can't be magic'd
 away.

 Plus the ARM64 image format is different from our zImage format.  It
 would make far *more* sense to align our Image format with our zImage
 format so existing boot loaders which look for the zImage magic numbers
 can boot plain Image files too.

 Moreover, since we could *never* align zImage with the ARM64 format,
 why on earth would we want to start using the ARM64 format for the
 Image format?

I'm not talking about zImage. I'm talking about Image files only. The
arm64 Image header could be added to ARM Image files and that would
not hurt or change a thing for existing users. The cost is 64 bytes.

 If you say, we should just break the existing zImage format, my response
 will be: who the hell are you to decide to break 20 odd years of boot
 ABI in a way which *stops* platforms from booting on such a pathetic
 whim.

I'm not suggesting to break anything or changing existing platforms,
but how do we improve the Image format in a compatible way. If
bootloaders want to support booting Image files or vmlinux directly,
then we should support that including any compatible changes to make
things work better.

Rob
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-16 Thread Nicolas Pitre 
On Wed, 16 Apr 2014, Christopher Covington wrote:

 On 04/15/2014 06:44 AM, Daniel Thompson wrote:
  Hi Folks
  
  I've just been rebasing some of my development branches against v3.15rc1
  and observed some boot regressions due to TEXT_OFFSET changing from
  0x8000 to 0x208000.
  
  Now the boot regression turned out to be fault in the JTAG boot tools I
  was using (it had internally hardcoded to TEXT_OFFSET to 0x8000 when
  calculating what physical load address to use). I've fixed the JTAG
  loader and my own boards now boots fine.
 
 Your tools are not alone in being affected by this change. QEMU is considering
 changing their hard-coded value to 0x8000 [1], which I was eager to see until
 being reminded of this (that patch would still be an improvement, but not
 enough for users of new multiplatform kernels).
 
 The boot-wrapper [2] (the default bootloader for ARM's proprietary models
 which could potentially be used on other systems) is also affected.

Why would QEMU and the ARM boot-wrap-per care about the kernel 
TEXT_OFFSET value?

I may understand the desire to boot a plain uncompressed Image over JTAG 
and in this case you are amongst a very small group of people doing so 
and therefore should be knowing what you're doing.  In other words this 
is a minor inconvenient to a few people.

But both QEMU and the boot-wrapper should deal with zImage. That's the 
only image format with documented load offset is guaranteed not to 
change i.e. it can be loaded at about any offset as zImage knows how to 
relocate itself as needed.  There is nowhere a guarantee that 
TEXT_OFFSET can't change.

And if you think booting zImage on ARM models is too slow, then simply 
try out CONFIG_KERNEL_LZO.

 My current thinking is that even if we temporarily removed variance (the
 jumping about) by maybe building every image with the maximum offset that any
 image could have, there would still be variance between images built before
 and after that change, and maybe also when some new platform gets added with
 an even higher offset. So if there's going to be variance, could we maybe make
 it no longer a problem?

There is already no problem with zImage.

 It seems to me that if external/uncompressed image loaders could query the
 text offset in a straightforward manner, variance between images could be
 easily dealt with. Would reading it out of ELF metadata be a reasonable
 mechanism? Could the ELF format vmlinux be a suitable general replacement for
 the raw Image?

The ELF image only has virtual addresses in it.  And the virtual address 
of the kernel may be changed independently of TEXT_OFFSET with 
CONFIG_VMSPLIT_*.

 Now at least with my current .config, the vmlinux only has virtual addresses.
 Documentation/arm/Booting says the MMU has to be off at boot time so this
 still might not be the ideal input for image loaders. Tools could hard-code
 the phsyical-to-virtual offset instead of the TEXT_OFFSET. Is that less likely
 to vary?

Physical offset does vary from one platform to another, so this 
particular physical-to-virtual offset is actually determined at run time 
and the kernel runtime patched during early boot -- see __fixup_pv_table 
in arch/arm/kernel/head.S.

 Or could we patch up the linker script to set zero-based ELF load
 memory addresses (LMAs) [4] so that the physical addresses are almost right,
 you just might have to add a system-specific RAM offset, perhaps pulled out of
 the device tree? If that won't work, we could generate some kind of
 vmlinux-phys with physical addresses. The latter two options might also
 simplify external debugging before __turn_mmu_on(). I like the sound of the
 LMA approach best, assuming it doesn't break existing stuff (I notice a few AT
 directives in vmlinux.lds.S). Some of this might transfer to arm64 as well.
 What do you all think?

If you really really want to get at the TEXT_OFFSET value in the 
uncompressed image, the simplest way would be:

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index f8c08839ed..de84d0635a 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -78,6 +78,11 @@
 
__HEAD
 ENTRY(stext)
+
+   b   1f
+   .word   TEXT_OFFSET @ located at a 4-byte offset in Image
+1:
+
  ARM_BE8(setendbe )@ ensure we are in BE8 mode
 
  THUMB(adr r9, BSYM(1f))   @ Kernel is always entered in 
ARM.

This way the first word for Image would always be 0xea00 and the 
second one would be TEXT_OFFSET.  No other kernel Image binaries ever 
had 0xea00 as their first word so that also let you validate whether 
or not the TEXT_OFFSET value is there.


Nicolas
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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-16 Thread Christopher Covington 
Hi Nicolas,

Thanks for your response.

On 04/16/2014 03:14 PM, Nicolas Pitre wrote:
 On Wed, 16 Apr 2014, Christopher Covington wrote:
 
 On 04/15/2014 06:44 AM, Daniel Thompson wrote:
 Hi Folks

 I've just been rebasing some of my development branches against v3.15rc1
 and observed some boot regressions due to TEXT_OFFSET changing from
 0x8000 to 0x208000.

 Now the boot regression turned out to be fault in the JTAG boot tools I
 was using (it had internally hardcoded to TEXT_OFFSET to 0x8000 when
 calculating what physical load address to use). I've fixed the JTAG
 loader and my own boards now boots fine.

 Your tools are not alone in being affected by this change. QEMU is 
 considering
 changing their hard-coded value to 0x8000 [1], which I was eager to see until
 being reminded of this (that patch would still be an improvement, but not
 enough for users of new multiplatform kernels).

 The boot-wrapper [2] (the default bootloader for ARM's proprietary models
 which could potentially be used on other systems) is also affected.
 
 Why would QEMU and the ARM boot-wrap-per care about the kernel 
 TEXT_OFFSET value?

The simulators I'm familiar with all have the equivalent of a built-in JTAG
debugger, capable of peeking at and poking memory, servicing Angel semihosting
calls, and so on. Knowledge of the TEXT_OFFSET is required for loading
non-self-uncompressing images for the same reasons as when using JTAG on real
hardware, as I understand it.

 I may understand the desire to boot a plain uncompressed Image over JTAG 
 and in this case you are amongst a very small group of people doing so 
 and therefore should be knowing what you're doing.  In other words this 
 is a minor inconvenient to a few people.

I didn't mean to imply that there is a large user base for this style of
loading, just that an approach that works across multiple tools would be nice
if change is warranted.

 But both QEMU and the boot-wrapper should deal with zImage. That's the 
 only image format with documented load offset is guaranteed not to 
 change i.e. it can be loaded at about any offset as zImage knows how to 
 relocate itself as needed.  There is nowhere a guarantee that 
 TEXT_OFFSET can't change.

QEMU definitely does support zImage and I believe it's promoted as the main
boot method. I would expect the bootwrapper to work with zImages, as its (in
the non-semihosting case) basically just packing the kernel, device tree and
initramfs up into an ELF file that's loaded into memory by a simulator's
built-in JTAG-like loader.

 And if you think booting zImage on ARM models is too slow, then simply 
 try out CONFIG_KERNEL_LZO.

Thanks for the tip.

 My current thinking is that even if we temporarily removed variance (the
 jumping about) by maybe building every image with the maximum offset that any
 image could have, there would still be variance between images built before
 and after that change, and maybe also when some new platform gets added with
 an even higher offset. So if there's going to be variance, could we maybe 
 make
 it no longer a problem?
 
 There is already no problem with zImage.
 
 It seems to me that if external/uncompressed image loaders could query the
 text offset in a straightforward manner, variance between images could be
 easily dealt with. Would reading it out of ELF metadata be a reasonable
 mechanism? Could the ELF format vmlinux be a suitable general replacement for
 the raw Image?
 
 The ELF image only has virtual addresses in it.  And the virtual address 
 of the kernel may be changed independently of TEXT_OFFSET with 
 CONFIG_VMSPLIT_*.

Do you know why this is the case? The ELF format is capable of storing
physical addresses as mentioned below.

 Now at least with my current .config, the vmlinux only has virtual addresses.
 Documentation/arm/Booting says the MMU has to be off at boot time so this
 still might not be the ideal input for image loaders. Tools could hard-code
 the phsyical-to-virtual offset instead of the TEXT_OFFSET. Is that less 
 likely
 to vary?
 
 Physical offset does vary from one platform to another, so this 
 particular physical-to-virtual offset is actually determined at run time 
 and the kernel runtime patched during early boot -- see __fixup_pv_table 
 in arch/arm/kernel/head.S.

What I meant to ask about was variance from one kernel version and build to
the next, given a single platform. Platform-to-platform variation can probably
be abstracted where needed by the scripts controlling the external load. In
any case, CONFIG_VMSPLIT_* that you mentioned above would be an example where
it would vary in an inconvenient manner, so this approach wouldn't be an
improvement.

 Or could we patch up the linker script to set zero-based ELF load
 memory addresses (LMAs) [4] so that the physical addresses are almost right,
 you just might have to add a system-specific RAM offset, perhaps pulled out 
 of

I don't think I made this very clear, but adding the offset would happen at

Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-16 Thread Russell King - ARM Linux 
On Wed, Apr 16, 2014 at 05:08:35PM -0400, Christopher Covington wrote:
 What I meant to ask about was variance from one kernel version and build to
 the next, given a single platform. Platform-to-platform variation can probably
 be abstracted where needed by the scripts controlling the external load. In
 any case, CONFIG_VMSPLIT_* that you mentioned above would be an example where
 it would vary in an inconvenient manner, so this approach wouldn't be an
 improvement.

No it wouldn't.  CONFIG_VMSPLIT_* has nothing to do with where the kernel
is loaded in physical memory.  That's all about how the kernel sets up the
page tables, and where the kernel eventually expects to run in the virtual
address space.

As far as the debugger goes, it still loads the kernel at the exact same
address irrespective of what CONFIG_VMSPLIT_* setting is chosen.

The issue here is with arm-soc's single zImage project sucking in existing
platforms where there's a requirement to keep the first N kB of memory
free from use - eg, because a boot loader likes to scribble over it, or
it's in use by a DSP processor, or something similar.

Once one of those platforms is merged and enabled in the single zImage,
the offset into RAM that the kernel must be loaded has to change to
avoid clashing on those platforms.

So, there really isn't one single Kconfig option you can point at to tell
what physical RAM offset the kernel needs to be loaded at... it depends
what platforms are enabled in the kernel you're trying to boot.

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Re: Change of TEXT_OFFSET for multi_v7_defconfig

2014-04-16 Thread Russell King - ARM Linux 
On Wed, Apr 16, 2014 at 10:36:11PM +0100, Peter Maydell wrote:
 On 16 April 2014 22:08, Christopher Covington c...@codeaurora.org wrote:
  On 04/16/2014 03:14 PM, Nicolas Pitre wrote:
  But both QEMU and the boot-wrapper should deal with zImage. That's the
  only image format with documented load offset is guaranteed not to
  change i.e. it can be loaded at about any offset as zImage knows how to
  relocate itself as needed.  There is nowhere a guarantee that
  TEXT_OFFSET can't change.
 
  QEMU definitely does support zImage and I believe it's promoted as the main
  boot method.
 
 Yes; we also support uImage. The code nominally handling Image
 actually currently loads at 0x1, so the set of people who actually
 try to use it is obviously not very large :-)

For ARM, that means precisely zero users without modification of that.
We've never supported an offset of 0x1 in mainline kernels.

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