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

[Samuel Martin <s.martin49@gmail.com>]

tl;dr:

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.

Note:
  If CMake-based project forces using a given build type and/or
  redefined the compiler and/or linker flags (the default ones or the
  per-config ones - e.g. CMAKE_C_FLAGS/CMAKE_C_FLAGS_{DEBUG,RELEASE} -,
  there is not much Buildroot can do about it.
  So, the flags will be overwritten anyway in these cases.

Cc: Charles Hardin <ckhardin@exablox.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
---
 package/pkg-cmake.mk | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/package/pkg-cmake.mk b/package/pkg-cmake.mk
index aca9e61..eb4ec7a 100644
--- a/package/pkg-cmake.mk
+++ b/package/pkg-cmake.mk
@@ -79,6 +79,16 @@ endif
 ifndef $(2)_CONFIGURE_CMDS
 ifeq ($(4),target)
 
+# Here we choose the CMake build type which matches the best the build
+# configuration set in Buildroot.
+ifeq ($(BR2_ENABLE_DEBUG),y)
+BR_CMAKE_BUILD_TYPE=Debug
+else ifeq ($(BR2_OPTIMIZE_S),y)
+BR_CMAKE_BUILD_TYPE=MinSizeRel
+else
+BR_CMAKE_BUILD_TYPE=Release
+endif
+
 # Configure package for target
 define $(2)_CONFIGURE_CMDS
 	(mkdir -p $$($$(PKG)_BUILDDIR) && \
@@ -87,7 +97,7 @@ define $(2)_CONFIGURE_CMDS
 	PATH=$$(BR_PATH) \
 	$$($$(PKG)_CONF_ENV) $$(BR2_CMAKE) $$($$(PKG)_SRCDIR) \
 		-DCMAKE_TOOLCHAIN_FILE="$$(HOST_DIR)/usr/share/buildroot/toolchainfile.cmake" \
-		-DCMAKE_BUILD_TYPE=$$(if $$(BR2_ENABLE_DEBUG),RelWithDebInfo,Release) \
+		-DCMAKE_BUILD_TYPE="$(BR_CMAKE_BUILD_TYPE)" \
 		-DCMAKE_INSTALL_PREFIX="/usr" \
 		-DCMAKE_COLOR_MAKEFILE=OFF \
 		-DBUILD_DOC=OFF \
-- 
2.10.0