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| -rw-r--r-- | doc/src/guide/ports.asciidoc | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/doc/src/guide/ports.asciidoc b/doc/src/guide/ports.asciidoc index 02c636f..907ee36 100644 --- a/doc/src/guide/ports.asciidoc +++ b/doc/src/guide/ports.asciidoc @@ -98,3 +98,37 @@ The source files are automatically gathered from the contents of '$(C_SRC_DIR)'. Erlang.mk looks for '.c', '.C', '.cc' and '.cpp' source files. You can define the variable `SOURCES` to manually list the files to compile. + +=== Propagating compile and linker flags to sub-Makefiles + +In some cases it might be necessary to propagate the flags +you just defined to the sub-Makefiles of your local project. +You generally can't just export those as this could impact +the building of dependencies. + +Makefiles allow you to export variables for specific targets. +When doing this, the variables will be exported only when +this target runs, and not for other targets. It is therefore +possible to export them when building the C code without +impacting other build steps. + +By adding this to your Makefile all five variables will be +made available to sub-Makefiles when building C code: + +[source,make] +---- +app-c_src: export CC += +app-c_src: export CFLAGS += +app-c_src: export CPPFLAGS += +app-c_src: export LDFLAGS += +app-c_src: export LDLIBS += +---- + +Appending an empty string to the existing value is necessary +because Makefiles expect an assignment for target-specific +exports. Alternatively you can set a new value: + +[source,make] +---- +app-c_src: export CFLAGS = -O3 +---- |