Build doesn't verify that setting config options worked

[broonie]

Nothing in the build code verifies that a .config that is generated from a config with additional options set actually sets those options, resulting in silent failures like those we see with clang and defconfig+CPU_BIG_ENDIAN. It would cost very little to grep the resulting config for these options and save a bunch of pain when things go wrong.

[gctucker]

Actually, merge_config.sh does check each config after merging. What it doesn't is propagate the error when there's a problem, but there's already a fix for that from you ;)

Here's an example output of when it fails to set CPU_BIG_ENDIAN:

Using build/.config as base
Merging build/frag.config
Value of CONFIG_CPU_BIG_ENDIAN is redefined by fragment build/frag.config:
Previous value: # CONFIG_CPU_BIG_ENDIAN is not set
New value: CONFIG_CPU_BIG_ENDIAN=y

make[1]: Entering directory '/home/buildslave/staging/workspace/gtucker/kernel-build/linux/build'
  HOSTCC  scripts/basic/fixdep
  GEN     Makefile
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  HOSTCC  scripts/kconfig/lexer.lex.o
  HOSTCC  scripts/kconfig/parser.tab.o
  HOSTCC  scripts/kconfig/preprocess.o
  HOSTCC  scripts/kconfig/symbol.o
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf  --alldefconfig Kconfig
scripts/Kconfig.include:35: compiler 'aarch64-linux-gnu-gcc' not found
make[2]: *** [../scripts/kconfig/Makefile:73: alldefconfig] Error 1
make[1]: *** [/home/buildslave/staging/workspace/gtucker/kernel-build/linux/Makefile:562: alldefconfig] Error 2
make[1]: Leaving directory '/home/buildslave/staging/workspace/gtucker/kernel-build/linux/build'
make: *** [Makefile:179: sub-make] Error 2
Value requested for CONFIG_CPU_BIG_ENDIAN not in final .config
Requested value:  CONFIG_CPU_BIG_ENDIAN=y
Actual value:     # CONFIG_CPU_BIG_ENDIAN is not set

[broonie]

Right, I'm aware that it complains but thought that this was a warning not an error. I see it is an error now but I suspect that's going to get changed for usability, we might get an option to turn it back into an error though.

[gctucker]

OK - in any case doing the check in merge_config.sh is what makes most sense to me, rather than in kci_build or some other tool outside of the kernel tree.

[gctucker]

Replaced with an issue in my kernel fork.