Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option

[乔崇 <qiaochong@loongson.cn>]

Hui Zhu 写道:
> In this way, you will got a lot of error.
>
> Hui
>
> On Mon, Nov 29, 2010 at 16:41, 乔崇 <qiaochong@loongson.cn> wrote:
>   
>> does not need change kernel,just write a shell mycc as bellow:
>>
>> #!/bin/sh
>> gcc "$@" -O0
>>
>>     
change mycc to this will work,:)

#!/bin/sh
gcc "$@" -O0 ||
 gcc "$@" -O1 ||
 gcc "$@"
 

>> then
>>
>> make CC=./mycc vmlinux
>>
>> Hui Zhu said
>>
>> On Mon, Nov 29, 2010 at 16:16, Américo Wang <xiyou.wangcong@gmail.com>
>> wrote:
>>
>>
>> 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.
>>
>>
>> If they really need O2, I set  them to O2.
>> Actually, this is the main work, find out the file that need the O2.  :)
>>
>> For example:
>> ifdef CONFIG_CC_CLOSE_OPTIMIZATION
>> CFLAGS_fpu.o                           += -O2
>> CFLAGS_aesni-intel_glue.o              += -O2
>> CFLAGS_ghash-clmulni-intel_glue.o      += -O2
>> endif
>>
>> And I will try to find more of these type files.
>>
>>
>>
>> Also, what is size of vmlinux before applying your patch and after that?
>> Does it increase too much?
>>
>>
>>
>> Before the patch:
>> ls -alh vmlinuz-2.6.37-rc3+
>> -rw-r--r-- 1 root root 4.1M 2010-11-25 12:02 vmlinuz-2.6.37-rc3+
>> ls -alh b26no/vmlinux
>> -rwxr-xr-x 1 teawater teawater 135M 2010-11-25 13:31 b26no/vmlinux
>>
>> After the patch:
>> ls -alh vmlinuz-2.6.37-rc3debug+
>> -rw-r--r-- 1 root root 4.6M 2010-11-25 14:02 vmlinuz-2.6.37-rc3debug+
>> ls -alh b26/vmlinux
>> -rwxr-xr-x 1 teawater teawater 140M 2010-11-25 11:14 b26/vmlinux
>>
>> Thanks,
>> Hui
>>
>>
>>
>>
>> --
>>
>> 乔崇 qiaochong@loongson.cn
>>
>> 2010年 11月 29日 星期一 16:35:38 CST
>>     
>
>
>   


-- 

乔崇 qiaochong@loongson.cn
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2010年 11月 29日 星期一 17:38:14 CST