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    SubjectRe: [PATCH] Built kernel without -O2 option
    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?
    -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

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      Last update: 2010-11-29 10:47    [W:0.023 / U:36.988 seconds]
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