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When a build type is set, CMake does append some flags that can override
those set by Buildroot due to the gcc option parser (in which the last
argument controling an option wins).
Hereafter is a summary of the optimization and debug flags set by
Buildroot and appended by CMake.
* 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_{0..3} | -On -gx
n | BR2_OPTIMIZE_S | -Os
n | BR2_OPTIMIZE_G | -Og
n | BR2_OPTIMIZE_{0..3} | -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
To avoid the CMake flags take precedence over the Buildroot ones, this
change sets in toolchainfile.cmake the per-config compiler flags CMake
can append depending on the build type Buildroot defined.
So, CMake does not mess up with the compilation flags Buildroot sets.
It is still possible to override these per-config flags on the cmake
command line.
Note:
If a CMake-based project forces the compiler and/or linker flag
definitions (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: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas:
- adjust comment in toolchainfile.cmake.in, as suggested by Arnout.
- also handle CMAKE_Fortran_FLAGS_*, as suggested by Arnout.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Buildroot is a simple, efficient and easy-to-use tool to generate embedded Linux systems through cross-compilation. The documentation can be found in docs/manual. You can generate a text document with 'make manual-text' and read output/docs/manual/manual.text. Online documentation can be found at http://buildroot.org/docs.html To build and use the buildroot stuff, do the following: 1) run 'make menuconfig' 2) select the target architecture and the packages you wish to compile 3) run 'make' 4) wait while it compiles 5) find the kernel, bootloader, root filesystem, etc. in output/images You do not need to be root to build or run buildroot. Have fun! Buildroot comes with a basic configuration for a number of boards. Run 'make list-defconfigs' to view the list of provided configurations. Please feed suggestions, bug reports, insults, and bribes back to the buildroot mailing list: buildroot@buildroot.org You can also find us on #buildroot on Freenode IRC. If you would like to contribute patches, please read https://buildroot.org/manual.html#submitting-patches