Re: [PATCH] Built kernel without -O2 option
From: Hui Zhu
Date: Wed Dec 01 2010 - 08:11:20 EST
On Tue, Nov 30, 2010 at 05:07, Arnaud Lacombe <lacombar@xxxxxxxxx> wrote:
> Hi,
>
> On Sun, Nov 28, 2010 at 10:56 PM, Hui Zhu <teawater@xxxxxxxxx> 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
>> $3 = <value optimized out>
>> And the code execution order is not right.
>>
>> This is becuase the Kernel is bult with gcc -O2. Gcc will not
>> generate enough debug message with file with -O2.
>> So GDB cannot work very well with Linux kernel.
>>
>> So I make a patch that add a option in "Kernel hacking" called "Close
>> GCC optimization". It will make kernel be built without -O2.
>>
> no, it does not, see below ..
>
>> I built and use it in i386 and x86_64. I will try to make it OK in other arch.
>>
>> And I will put new patch in here and
>> http://code.google.com/p/kgtp/downloads/list
>>
>> Thanks,
>> Hui
>>
>> Signed-off-by: Hui Zhu <teawater@xxxxxxxxx>
>> ---
>> [...]
>> +ifdef CONFIG_CC_CLOSE_OPTIMIZATION
>> +CFLAGS_process_$(BITS).o += -O2
>> +CFLAGS_entry_$(BITS).o += -O2
>> +CFLAGS_traps.o += -O2
>> +CFLAGS_i387.o += -O2
>> +CFLAGS_xsave.o += -O2
>> +CFLAGS_hpet.o += -O2
>> +endif
>>
>> [...]
>>
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -136,6 +136,14 @@ config DEBUG_SECTION_MISMATCH
>> - Enable verbose reporting from modpost to help solving
>> the section mismatches reported.
>>
>> +config CC_CLOSE_OPTIMIZATION
>> + bool "Close GCC optimization"
>> + default n
>> + help
>> + Enabling this option will let gcc build kernel without "-O2".
>> +
>> + If unsure, say N.
>> +
> You are not consistent with yourself, you add an option saying "do not
> build the kernel with -O2" and yet, you add "-O2" flags for unknown
> reason all over the tree...
>
> - Arnaud
>
You are really good at English. But not mathematics.
Add -O2 to build 30 files is better than add -O2 to all files(who know
how much files in Linux Kernel?).
Thanks,
Hui
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