Vfrdtyky

Whenever I try to work with kernel source (be it upstream to higher Linux stable version, adding features, etc.), it fails on random source files when compiling.

For example, I tried to upstream kernel version from v3.18.110 to 3.18.125 (with one version at a time, of course). I successfully resolved all conflicts which appeared, but when I start building the kernel, the compiler finds error in file which wasn't even in the conflicting files. Solving the error which appears will introduce more errors, either in the same file or in other file.

Other thing I tried is adding a governor. I successfully added the code where it is needed, added the original governor source file, then enabled it in default config and then started compiling. After this, the compiler found some error in the .c file of the governor. Why?

I'm not asking for error resolution, I want to know why errors happen in the first place.

Architecture is arm64, toolchain is:
https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9

Example:
I'm trying to add governor by editing these files:

drivers/cpufreq/Kconfig

drivers/cpufreq/Makefile

include/linux/cpufreq.h

Kconfig:

config CPU_FREQ_DEFAULT_GOV_SMARTMAX

bool "smartmax"

select CPU_FREQ_GOV_SMARTMAX

help

  Use the CPUFreq governor 'smartmax' as default



config CPU_FREQ_GOV_SMARTMAX

 tristate "'smartmax' cpufreq policy governor"  

 select CPU_FREQ_TABLE  

 help   

   'smartmax' combined ondemand and smartass2

Makefile:

obj-$(CONFIG_CPU_FREQ_GOV_SMARTMAX) += cpufreq_smartmax.o

cpufreq.h:

#elif defined(CONFIG_CPU_FREQ_DEFAULT_GOV_SMARTMAX)

extern struct cpufreq_governor cpufreq_gov_smartmax;

#define CPUFREQ_DEFAULT_GOVERNOR    (&cpufreq_gov_smartmax)

After that I add the .c file of the governor (which is unmodified and completely original governor code), then add this in default config for my device:

CONFIG_CPU_FREQ_GOV_SMARTMAX=y

Then I go to toolchain folder, open terminal and type this:

export CROSS_COMPILE=$(pwd)/bin/aarch64-linux-android-

export ARCH=arm64 && export SUBARCH=arm64

After this I go to kernel folder and use the following commands:

make clean

make mrproper

make *my_device_config_name*

make -s -j$(nproc --all)

Doing all of this results in the following errors in the governor code:

drivers/cpufreq/cpufreq_smartmax.c: In function 'cpufreq_smartmax_timer':
drivers/cpufreq/cpufreq_smartmax.c:522:3: error: implicit declaration of function '__cpufreq_driver_getavg' [-Werror=implicit-function-declaration]
freq_avg = __cpufreq_driver_getavg(policy, j);

drivers/cpufreq/cpufreq_smartmax.c: In function 'store_debug_mask':
drivers/cpufreq/cpufreq_smartmax.c:607:2: error: implicit declaration of function 'strict_strtoul' [-Werror=implicit-function-declaration]
res = strict_strtoul(buf, 0, &input);

The smartmax cpufreq governor was designed for older Linux kernels (likely pre-3.4). Hence, it still references several outdated kernel APIs and functions. Since these APIs are no longer in Linux 3.18, compilation errors occur.

drivers/cpufreq/cpufreq_smartmax.c: In function 'cpufreq_smartmax_timer': drivers/cpufreq/cpufreq_smartmax.c:522:3: error: implicit declaration of function '__cpufreq_driver_getavg' [-Werror=implicit-function-declaration] freq_avg = __cpufreq_driver_getavg(policy, j);

Specifically, this error is caused by the governor utilizing the __cpufreq_driver_getavg() function, which is no longer present in Linux 3.18. In fact, the function was removed in Linux 3.12, 5 years ago in 2013. To fix the compilation error, you could revert that commit and resolve any Git conflicts. However, there may still be other issues (compatibility, compilation, etc.) along the way.

drivers/cpufreq/cpufreq_smartmax.c: In function 'store_debug_mask': drivers/cpufreq/cpufreq_smartmax.c:607:2: error: implicit declaration of function 'strict_strtoul' [-Werror=implicit-function-declaration] res = strict_strtoul(buf, 0, &input);

Similarly, strict_strtoul() is another function that is no longer in Linux 3.18, but is still utilized by the smartmax governor. Thankfully, this issue is trivial to fix. You can simply replace any uses of strict_strtoul with kstrtoul, which serves pretty much the same purpose.

I am fairly certain that there are other outdated or removed kernel APIs and functions that the smartmax governor depends on. You could attempt to update the governor for Linux 3.18, but it may not be worth the time and effort.