Re: [PATCH] Built kernel without -O2 option

On Mon, Nov 29, 2010 at 17:44, Christian Borntraeger
<borntraeger <at> de.ibm.com> wrote:
> Am 29.11.2010 09:16, schrieb Américo Wang:
>> On Mon, Nov 29, 2010 at 11:56:15AM +0800, Hui Zhu wrote:
>>> Hi,
>>>
>>> Now, there are a lot of ways to debug the Linux kernel with GDB, like
>>> qemu, kgtp or kgdb and so on.
>>> But the developer more like add a printk. It have a lot of reason, a big one is:
>>> (gdb) p ret
>>> $3 = <value optimized out>
>>> And the code execution order is not right.
>>>
>>> This is becuase the Kernel is bult with gcc -O2.  Gcc will not
>>> generate enough debug message with file with -O2.
>>> So GDB cannot work very well with Linux kernel.
>>>
>>> So I make a patch that add a option in "Kernel hacking" called "Close
>>> GCC optimization".  It will make kernel be built without -O2.
>>>
>>> I built and use it in i386 and x86_64.  I will try to make it OK in other arch.
>>>
>>
>> The problem is that some functions _have to_ be inlined and gcc without -O2
>> doesn't inline them. Have check all the cases? I doubt.
>
> In essence -O2 just tells gcc to activate a list of optimizations
> gcc  -Q -O2 --help=optimizers
> tells you what.
>