Re: Writing a BSP from downstream kernel sources

Joel A Cohen

I'm not sure if this is your issue, but I had a similar issue ilog2 and the disassembler and fixed it by backporting this patch.

No guarantees, but perhaps it will help.


On Fri, Jan 29, 2021 at 9:51 PM Jonas Vautherin <jonas.vautherin@...> wrote:
Thanks a lot for the advice! However, I can't seem to find a `const` that I can simply remove. To give more context, here is the log output around such an error (it seems like it is often surrounded by this log2.h warning, by the way):

| In file included from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/kernel.h:11,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/kallsyms.h:9,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/ftrace.h:10,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/kernel/extable.c:18:
| /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/log2.h:22:1: warning: ignoring attribute 'noreturn' because it conflicts with attribute 'const' [-Wattributes]
|    22 | int ____ilog2_NaN(void);
|       | ^~~
|   CC      fs/fat/dir.o
| In file included from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/kernel.h:11,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/list.h:8,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/module.h:9,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/fs/fat/dir.c:16:
| /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/log2.h:22:1: warning: ignoring attribute 'noreturn' because it conflicts with attribute 'const' [-Wattributes]
|    22 | int ____ilog2_NaN(void);
|       | ^~~
|   CC      block/deadline-iosched.o
| In file included from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/kernel.h:11,
|                  from /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/block/deadline-iosched.c:6:
| /home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/include/linux/log2.h:22:1: warning: ignoring attribute 'noreturn' because it conflicts with attribute 'const' [-Wattributes]
|    22 | int ____ilog2_NaN(void);
|       | ^~~
| /tmp/cc52vFrQ.s: Assembler messages:
| /tmp/cc52vFrQ.s:2683: Error: .err encountered
| /tmp/cc52vFrQ.s:2927: Error: .err encountered
|   LD      sound/sparc/built-in.o
|   LD      sound/spi/built-in.o
| make[3]: *** [/home/jones/Documents/yocto/poky/build/tmp/work-shared/skycontroller3/kernel-source/scripts/ block/scsi_ioctl.o] Error 1

I pasted the full output here, if that can help: The lines that seem to get the log2 warning are:

extern __attribute__((const, noreturn))
int ____ilog2_NaN(void);

So there is a const there, but well... not sure what to do with it :-).


On Mon, Jan 25, 2021 at 9:00 AM Diego Santa Cruz <Diego.SantaCruz@...> wrote:

From: yocto@... <yocto@...> On Behalf Of Jonas Vautherin via
Sent: 24 January 2021 14:30
To: Jonas Vautherin <jonas.vautherin@...>
Cc: Paul Barker <pbarker@...>; Yocto-mailing-list <yocto@...>
Subject: Re: [yocto] Writing a BSP from downstream kernel sources


Just to close this: it seems like the gcc-cross-arm used by yocto gatesgarth is too new for that specific downstream kernel (3.18.31).


The goal was to get a proper BSP package for this device for a modern yocto, so I don't think I will try with an older version of Yocto. If I compile an old gcc as part of a custom Yocto layer (on gatesgarth), I am guessing that I will have issues creating a distro that runs both on RPi and on that older device (because RPi will have a newer kernel and gcc, and the skycontroller will use older ones). I also guess that the downstream dts won't work with a modern kernel, and I would not know how to write one myself for that apq8009 chip.


Hence, I'm giving up. Thanks a lot for the help :-).

[Diego Santa Cruz] Wait! You may be able to get it working, see below.


On Sat, Jan 23, 2021 at 2:07 PM Jonas Vautherin via <> wrote:

Thanks a lot for the answer!


It seems like using `KCONFIG_MODE = "--alldefconfig"` with `KBUILD_DEFCONFIG = "msm8909_defconfig"` now ends up with the same kind of errors as when I use the defconfig from the downstream kernel [1], i.e.:


[Diego Santa Cruz] I happen to be doing a similar kind of work, getting an even older (2.6.37+) downstream kernel for an ARM machine to compile with recent GCC in Yocto, in my case GCC 9.3 from dunfell. There are a few fixes and backports necessary to make it happen and boot. I’m not done with the work yet, so I do not know how stable it is, but I have it booting.


| /tmp/ccz8jKgm.s: Assembler messages:
| /tmp/ccz8jKgm.s:985: Error: .err encountered


[Diego Santa Cruz] The fix here is rather simple once you understand what’s going on, the problem is abusive use of const for register variables, see so when put_user() is used for a literal constant value it gets assigned the wrong register, so just remove the const qualifier from the put_user() register variable assignment for the value argument. For my older kernel the patch is like this.

--- arch/arm/include/asm/uaccess.h

+++ arch/arm/include/asm/uaccess.h

@@ -145,7 +145,7 @@

 #define put_user(x,p)                                                                                                    \

                ({                                                                                                                             \

-                               register const typeof(*(p)) __r2 asm("r2") = (x); \

+                              register typeof(*(p)) __r2 asm("r2") = (x);                             \

                                register const typeof(*(p)) __user *__p asm("r0") = (p);\

                                register int __e asm("r0");                                                           \

                        switch (sizeof(*(__p))) {                                                \


Could it be related to the tuning, e.g. I'm somehow defining a wrong toolchain in my machine configuration [2] and it fails to build? I was thinking about the include, though it seems to me that the apq8009 is a cortexa7 [3]:


[Diego Santa Cruz] Other commits from post 3.18 that you may need to backport are the following (start from bottom of list)

474c90156c8dcc2fa815e6716cc9394d7930cb9c give up on gcc ilog2() constant optimizations

cb984d101b30eb7478d32df56a0023e4603cba7f compiler-gcc: integrate the various compiler-gcc[345].h files

f6d133f877c8bb0a0934dc8c521c758ee771e901 compiler-gcc.h: neatening

7829fb09a2b4268b30dd9bc782fa5ebee278b137 lib: make memzero_explicit more robust against dead store elimination

cb4188ac8e5779f66b9f55888ac2c75b391cde44 compiler: introduce __alias(symbol) shortcut

0b053c9518292705736329a8fe20ef4686ffc8e9 lib: memzero_explicit: use barrier instead of OPTIMIZER_HIDE_VAR

ee91ef6173e81819f5ff610c2485802081635657 bufferhead: force inlining of buffer head flag operations

cc7fce80229067890365c1ee196be5d304d36dea mtd: blkdevs: fix switch-bool compilation warning



> The Qualcomm Snapdragon 212 APQ8009 is an entry level SoC for Android based tablets and smartphones. It contains four ARM Cortex-A7 CPU cores (quad core)





On Sat, Jan 23, 2021 at 11:06 AM Paul Barker <pbarker@...> wrote:

On Sat, 23 Jan 2021 at 02:29, Jonas Vautherin <jonas.vautherin@...> wrote:
> As a learning experience, I am trying to create a BSP for a device I own and whose downstream kernel is published. The device in question is the Parrot Skycontroller3, and the sources are available here.
> Let me start by sharing my issue. When I build the kernel with `bitbake virtual/kernel`, it fails with errors like:
> ```
> |   AS      arch/arm/lib/backtrace.o
> |   AS      arch/arm/lib/bswapsdi2.o
> |   AS      arch/arm/lib/call_with_stack.o
> | /tmp/ccz8jKgm.s: Assembler messages:
> | /tmp/ccz8jKgm.s:985: Error: .err encountered
> | /tmp/ccz8jKgm.s:1033: Error: .err encountered
> | /tmp/ccz8jKgm.s:6812: Error: .err encountered
> ```
> My layer is available here.
> I created it getting inspiration from meta-raspberrypi and meta-qti-bsp, which seems to have the same CPU: apq8009. According to the Parrot sources, my device runs a Qualcomm apq8009/msm89090 cpu. In my repo, I use as a defconfig file the linux.config that is available in the Parrot sources (I copied it in my kernel recipe under `files/defconfig` and added it to SRC_URI).
> The Parrot sources also refer to `LINUX_DEFAULT_CONFIG_TARGET := msm8909_defconfig`, so I tried to set `KBUILD_DEFCONFIG = "msm8909_defconfig"`, but that is failing with different errors, such as:
> ```
> error: 'VM_ARM_DMA_CONSISTENT' undeclared (first use in this function); did you mean 'DMA_ATTR_NON_CONSISTENT'?
> ```
> or
> ```
> error: 'L_PTE_YOUNG' undeclared
> ```
> As a side note, their `drivers/Kconfig` seemed invalid, so I patched it.
> I am a bit lost now, not completely sure where my issues come from. I realize that changing the defconfig has quite some impact (I get different errors), and also that my machine configuration may be completely wrong (I am essentially guessing from the fact that it is an apq8009/msm8909, but for instance the tuning I just copied from meta-qti-bsp, which may be invalid).
> I would be glad if I could get hints about debugging this. Again, it is really a learning project: I would like to learn how to create a BSP from a downstream kernel.

I think setting `KBUILD_DEFCONFIG = "msm8909_defconfig"` is likely the
correct approach here. What you may be missing though is the correct
value for KCONFIG_MODE. By default, the supplied defconfig file is
copied to .config but dependencies between config options aren't
resolved. You need to set `KCONFIG_MODE = "--alldefconfig"` to get the
equivalent of `make msm8909_defconfig` to occur. See
for an idea of how this is done for Raspberry Pi.


Paul Barker
Konsulko Group

Diego Santa Cruz, PhD
Technology Architect

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