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    SubjectRe: [PATCH] Built kernel without -O2 option
    On Mon, Nov 29, 2010 at 17:44, Christian Borntraeger
    <> wrote:
    > Am 29.11.2010 09:16, schrieb Américo Wang:
    >> 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.
    > In essence -O2 just tells gcc to activate a list of optimizations
    > gcc  -Q -O2 --help=optimizers
    > tells you what.
    > So what about making this patch much smaller by explicitely using the optimizations
    > that are absolutely necessary?
    > e.g:
    > -finline-small-functions -finline-functions-called-once
    > (what else do we need?)
    > We might even  be able to collapse this with the optimize for size option,
    > by providing a Kconfig entry that allows to choose between
    > -O0 -finline-small-functions -finline-functions-called-once
    > -O1 -finline-small-functions -finline-functions-called-once
    > -Os
    > -O2
    > -O3
    > Christian

    Hi Christian.

    If we can build without any optimization options just set some file to O2.
    I think keep it it will better than add some optimization options to
    all files, right?

    But make for this file that I add O2 to them, I can change them to to
    some others options like "-O0 -finline-small-functions

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