From: Changbin Du <changbin.du@xxxxxxxxx> Hi all, I know some kernel developers was searching for a method to dissable GCC optimizations, probably they want to apply GCC '-O0' option. But since Linux kernel replys on GCC optimization to remove some dead code, so '-O0' just breaks the build. They do need this because they want to debug kernel with qemu, simics, kgtp or kgdb. Thanks for the GCC '-Og' optimization level introduced in GCC 4.8, which offers a reasonable level of optimization while maintaining fast compilation and a good debugging experience. It is similar to '-O1' while perfer keeping debug ability over runtime speed. With '-Og', we can build a kernel with better debug ability and little performance drop after some simple change. In this serias, firstly introduce a new config CONFIG_NO_AUTO_INLINE after two fixes. Selecting this option will make compiler not auto-inline kernel functions.This is useful when you are using ftrace to understand the control flow of kernel code or tracing some static functions. Then introduce new config CONFIG_DEBUG_EXPERIENCE which apply '-Og' optimization level for whole kernel, with a simple fix in fix_to_virt(). Currently this option is only tested on a QEMU gust and it works fine. Comparison of vmlinux size: a bit smaller. w/o CONFIG_DEBUG_EXPERIENCE $ size vmlinux text data bss dec hex filename 22665554 9709674 2920908 35296136 21a9388 vmlinux w/ CONFIG_DEBUG_EXPERIENCE $ size vmlinux text data bss dec hex filename 21499032 10102758 2920908 34522698 20ec64a vmlinux Comparison of system performance: a bit drop. w/o CONFIG_DEBUG_EXPERIENCE $ time make -j4 real 6m43.619s user 19m5.160s sys 2m20.287s w/ CONFIG_DEBUG_EXPERIENCE $ time make -j4 real 6m55.054s user 19m11.129s sys 2m36.345s Changbin Du (5): x86/mm: surround level4_kernel_pgt with #ifdef CONFIG_X86_5LEVEL...#endif regulator: add dummy of_find_regulator_by_node kernel hacking: new config NO_AUTO_INLINE to disable compiler atuo-inline optimizations kernel hacking: new config DEBUG_EXPERIENCE to apply GCC -Og optimization asm-generic: fix build error in fix_to_virt with CONFIG_DEBUG_EXPERIENCE Makefile | 10 ++++++++++ arch/x86/include/asm/pgtable_64.h | 2 ++ arch/x86/kernel/head64.c | 13 ++++++------- drivers/regulator/internal.h | 9 +++++++-- include/asm-generic/fixmap.h | 3 ++- include/linux/compiler-gcc.h | 2 +- include/linux/compiler.h | 2 +- lib/Kconfig.debug | 34 ++++++++++++++++++++++++++++++++++ 8 files changed, 63 insertions(+), 12 deletions(-) -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html