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

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Message-ID: <AANLkTim44iCdyTsgXohL7TxWCi7=fA8RRZg3kuqUVczx@mail.gmail.com>
Date:	Wed, 1 Dec 2010 21:24:25 +0800
From:	Hui Zhu <teawater@...il.com>
To:	hellogcc@...elists.org
Cc:	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, gdb@...rceware.org
Subject: Re: [hellogcc] Re: [PATCH] Built kernel without -O2 option

2.6.35.4 is a little old.

What I try is 2.6.37-rc3+ and 2.6.37-rc4+ amd64 and i386.

Thanks,
Hui

2010/12/1 bekars <bekars@...il.com>:
> 这个好像不行，我在2.6.35.4内核上编译，报错：
>
>  ./mm.sh -Wp,-MD,arch/x86/kernel/.entry_32.o.d  -nostdinc -isystem
> /usr/lib/gcc/i486-linux-gnu/4.3.2/include
> -I/home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include
> -Iinclude  -include include/generated/autoconf.h -D__KERNEL__
> -D__ASSEMBLY__ -m32 -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1
> -DCONFIG_AS_CFI_SECTIONS=1  -gdwarf-2        -c -o
> arch/x86/kernel/entry_32.o arch/x86/kernel/entry_32.S
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:
> Assembler messages:
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:46:
> Error: unknown pseudo-op: `.cfi_sections'
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:
> Assembler messages:
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:46:
> Error: unknown pseudo-op: `.cfi_sections'
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:
> Assembler messages:
> /home/baiyu/Melon/RSW3/base_system/linux.DEV/LKGDB/arch/x86/include/asm/dwarf2.h:46:
> Error: unknown pseudo-op: `.cfi_sections'
> make[2]: *** [arch/x86/kernel/entry_32.o] Error 1
> make[1]: *** [arch/x86/kernel] Error 2
> make: *** [arch/x86] Error 2
>
>
>
> 在 2010年11月29日 下午5:45，乔崇 <qiaochong@...ngson.cn> 写道：
>> 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@...ngson.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@...il.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@...ngson.cn
>>>>
>>>> 2010年 11月 29日 星期一 16:35:38 CST
>>>>
>>>
>>>
>>>
>>
>>
>> --
>>
>> 乔崇 qiaochong@...ngson.cn
>> 龙芯中科技术服务中心有限公司
>> office:010-62600855-615
>> mobile:13521990614
>>
>> 2010年 11月 29日 星期一 17:38:14 CST
>>
>>
>
>
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