From: Michal Marek on
On 07/14/2010 03:43 PM, Andi Kleen wrote:
> Kbuild: Add option to set -femit-struct-debug-baseonly
>
> Newer gcc has a -femit-struct-debug-baseonly option that dramatically
> reduces the size of object files with debug info. What it does
> is to only emit type information for structures when the structures
> are defined in the same file or in a header file.
>
> This means the type information for most headers are not included.
> This is not good when the type information is actually
> needed (e.g. with kgdb or systemtap)
>
> But often kernel hackers only care about line numbers and don't
> need all the type information anyways. In this case setting
> the option can be a big win:
>
> A build dir for a specific x86-64 configuration with gcc 4.5
> shrunk from 2.3G to 1.2G. The compilation was also nearly a minute
> faster.
>
> Signed-off-by: Andi Kleen <ak(a)linux.intel.com>
>
> ---
> Makefile | 4 ++++
> lib/Kconfig.debug | 12 ++++++++++++
> 2 files changed, 16 insertions(+)
>
> Index: linux-2.6.34-ak/Makefile
> ===================================================================
> --- linux-2.6.34-ak.orig/Makefile
> +++ linux-2.6.34-ak/Makefile
> @@ -554,6 +554,10 @@ KBUILD_CFLAGS += -g
> KBUILD_AFLAGS += -gdwarf-2
> endif
>
> +ifdef CONFIG_DEBUG_INFO_REDUCED
> +KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly)
> +endif
> +
> ifdef CONFIG_FUNCTION_TRACER
> KBUILD_CFLAGS += -pg
> endif
> Index: linux-2.6.34-ak/lib/Kconfig.debug
> ===================================================================
> --- linux-2.6.34-ak.orig/lib/Kconfig.debug
> +++ linux-2.6.34-ak/lib/Kconfig.debug
> @@ -616,6 +616,18 @@ config DEBUG_INFO
>
> If unsure, say N.
>
> +config DEBUG_INFO_REDUCED
> + bool "Reduce debugging information"
> + depends on DEBUG_INFO
> + help
> + If you say Y here gcc is instructed to generate less debugging information
> + for structure types. This means that tools that need full debugging information
> + (like kgdb or systemtap) won't be happy. But if you merely need debugging
> + information to resolve line numbers there is no loss.
> + Advantage is that build directory object sizes shrink dramatically over
> + a full DEBUG_INFO build and compile times are reduced too.
> + Only works with newer gcc versions.
> +

I reformatted this help text to not wrap in a 80-column terminal and
applied the patch to the kbuild tree.

thanks,
Michal
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