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    SubjectRe: [PATCH] Built kernel without -O2 option
    On Mon, Nov 29, 2010 at 04:24:42PM +0800, Hui Zhu wrote:
    >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

    No, I didn't mean this, I meant some function that have to be inlined
    are those who only work when being inlined, e.g. current_text_addr().

    I think it is not alone. :)

    Also, since many inline functions sit in hot-path, are there any
    performance regressions with your patch applied?

    BTW, you need to Cc kbuild for makefile changes like this.
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      Last update: 2010-11-29 09:51    [W:0.023 / U:15.356 seconds]
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