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    SubjectRe: [hellogcc] Re: [PATCH] Built kernel without -O2 option
    On Mon, Nov 29, 2010 at 16:55, Steven <mqyoung@gmail.com> wrote:
    > I replace -O2 with -O0 in Makefile of kernel source code root directory?
    > I just do it and my gdb works well with this method.
    >
    > You mean it is not enough?
    >
    > Steven

    Yes.

    >
    > On Mon, 2010-11-29 at 16:47 +0800, Hui Zhu wrote:
    >> 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
    >> >
    >> > 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
    >
    >
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