Is it possible to turn off the gcc optimization when compiling kernel?

[Nicholas Mc Guire]

On Sun, Mar 20, 2016 at 02:46:41PM +0800, Hao Lee wrote:
> Hi,
> When I am debugging the linux kernel, I find that the execution
> sequence of some code is very strange. I think I need to turn off gcc
> optimization by  changing "-O2" to "-O0". But I encounter many errors.
> So, I want to know is it possible to turn off the gcc optimization or
> how can I compile some functions without optimization.

You can not turn it off in all functions as some need particluar 
optimization flags to comile at all, but you can pass 
individual CFLAGS per file via the Makefile

CFLAGS_target.o = -O0 or -flags-to-use

aswell as remove specific CFLAGS with

CFLAGS_REMOVE_target.o = -flags-to-remove

but if you want to debug the kernel it is most likely not
a good idea to try and disable optimization as the code you then
are debugging might not have that much to do with the final code
once optimization is on again. So simply generate the .lst file
of the target you are trying to debug e.g. for kernel/sched/core.c:

make kernel/sched/core.lst

and then use that .lst file to understand the output of gdb you
are inspecting.

thx!
hofrat