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    SubjectRe: [PATCH] Built kernel without -O2 option
    On Mon, Nov 29, 2010 at 16:16, Américo Wang <> wrote:
    > On Mon, Nov 29, 2010 at 11:56:15AM +0800, Hui Zhu wrote:
    >>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:
    CFLAGS_fpu.o += -O2
    CFLAGS_aesni-intel_glue.o += -O2
    CFLAGS_ghash-clmulni-intel_glue.o += -O2

    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

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      Last update: 2010-11-29 09:27    [W:0.023 / U:4.092 seconds]
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