How to pass compiler options during Linux kernel compilation?

Question

For reasons, I need to compile the Linux kernel (currently 4.7.10) passing some simple and innocent additional command line options (e.g. -pipe -Wsomething etc) to the C compiler.

How do I do it?

More specifically, how do I enforce these compiler flags during plain make as well as during make menuconfig and similar, i.e. so that they are always passed to the C compiler whenever the latter is executed.

Answer 1

From Linux kernel's makefile:

# Add any arch overrides and user supplied CPPFLAGS, AFLAGS and CFLAGS as the
# last assignments
KBUILD_CPPFLAGS += $(ARCH_CPPFLAGS) $(KCPPFLAGS)
KBUILD_AFLAGS   += $(ARCH_AFLAGS)   $(KAFLAGS)
KBUILD_CFLAGS   += $(ARCH_CFLAGS)   $(KCFLAGS)

So, passing additional options for Kbuild uses usual environment/makefile variables but with K prefix:

make "KCFLAGS=-pipe -Wsomething"

Answer 2

Kbuild — The Linux Kernel documentation provides a list of options,

• KCPPFLAGS

  Additional options to pass when preprocessing. The preprocessing options will be used in all cases where kbuild does preprocessing including building C files and assembler files.

• KAFLAGS

  Additional options to the assembler (for built-in and modules).

• AFLAGS_MODULE

  Additional assembler options for modules.

• AFLAGS_KERNEL

  Additional assembler options for built-in.

• KCFLAGS

  Additional options to the C compiler (for built-in and modules).

• CFLAGS_KERNEL

  Additional options for $(CC) when used to compile code that is compiled as built-in.

• CFLAGS_MODULE

  Additional module specific options to use for $(CC).

• LDFLAGS_MODULE

  Additional options used for $(LD) when linking modules.

• HOSTCFLAGS

  Additional flags to be passed to $(HOSTCC) when building host programs