[Buildroot] [PATCH v3 1/8] package/pkg-cmake.mk: fix build type and optimization flags

[Thomas Petazzoni]

Hello,

On Sat, 15 Oct 2016 11:44:30 +0200, Samuel Martin wrote:

> Before applying this patch, CMake packages are built with the following
> options:
>   * if BR2_ENABLE_DEBUG is set:
>     The CMake build type is set to RelWithDebInfo, which means:
>     - Optimization level is forced to: -O2;
>     - no log nor assert due to -DNDEBUG;
>     - BR2_DEBUG_{1..3} effect is unchanged;
>   * otherwise:
>     The CMake build type is set to Release, which means:
>     - Optimization level is forced to: -O3;
>     - no log nor assert due to -DNDEBUG (as expected).
>   In any case, the optimization WRT the binary size is always ignored and
>   forced.
> 
> This change chooses the build type doing the closest thing to what
> Buildroot attempts to do.
> 
> Long version:
> 
> Flags set by Buildroot depending on the configuration:
> 
>   BR2_ENABLE_DEBUG | Optim. level   | Buildroot {C,CXX}FLAGS
>   =================+================+=======================
>           y        | BR2_OPTIMIZE_S | -Os -gx
>           y        | BR2_OPTIMIZE_G | -Og -gx
>           y        | BR2_OPTIMIZE_n | -On -gx
>           n        | BR2_OPTIMIZE_S | -Os
>           n        | BR2_OPTIMIZE_G | -Og
>           n        | BR2_OPTIMIZE_n | -On
> 
> Default flags appended by CMake depending on the build type:
> 
>   Build type     | Flags           | Effects on {C,CXX}FLAGS
>   ===============+=================+===========================================
>   Debug          | -g              | Force -g, compatible with BR2_ENABLE_DEBUG
>   MinSizeRel     | -Os -DNDEBUG    | Set -Os, compatible with BR2_OPTIMIZE_S
>   Release        | -O3 -DNDEBUG    | Set -O3, closest to the others cases,
>                  |                 | though the optimization level is forced.
>   RelWithDebInfo | -O2 -g -DNDEBUG | Force -g and set -O2, not friendly with BR
> 
> Since CMake appends its own build type flags and because of the gcc
> option parser, the CMake flags takes precedence over the Buildroot
> flags.
> 
> So, this change sets the correct build type depending on the
> BR2_ENABLE_DEBUG and BR2_OPTIMIZE_* options.

Can't we tell CMake to not do all this crap, and simply not add
-g/-O<x> options by itself ?

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com