eigen: add hello world

Mention openmp on readme

kernel_module/external.mk

@@ -11,9 +11,14 @@ KERNEL_MODULE_SITE_METHOD = local
 ifeq ($(BR2_PACKAGE_OPENBLAS),y)
 	KERNEL_MODULE_DEPENDENCIES += openblas
 endif
+ifeq ($(BR2_PACKAGE_EIGEN),y)
+	KERNEL_MODULE_DEPENDENCIES += eigen
+endif
 
 define KERNEL_MODULE_BUILD_CMDS
-	$(MAKE) -C '$(@D)/user' $(TARGET_CONFIGURE_OPTS) BR2_PACKAGE_OPENBLAS="$(BR2_PACKAGE_OPENBLAS)"
+	$(MAKE) -C '$(@D)/user' $(TARGET_CONFIGURE_OPTS) \
+	  BR2_PACKAGE_OPENBLAS="$(BR2_PACKAGE_OPENBLAS)" \
+	  BR2_PACKAGE_EIGEN="$(BR2_PACKAGE_EIGEN)"
 endef
 
 define KERNEL_MODULE_INSTALL_TARGET_CMDS

kernel_module/user/Makefile

@@ -10,7 +10,13 @@ OUTS := $(foreach IN_EXT,$(IN_EXT_C) $(IN_EXT_CXX),$(addsuffix $(OUT_EXT), $(bas
 ifeq ($(BR2_PACKAGE_OPENBLAS),y)
 	LIBS += -lopenblas
 else
-	OUTS := $(filter-out openblas.out,$(OUTS))
+	OUTS := $(filter-out openblas$(OUT_EXT),$(OUTS))
+endif
+ifeq ($(BR2_PACKAGE_EIGEN),y)
+	# Header only.
+	#LIBS += -leigen
+else
+	OUTS := $(filter-out eigen%$(OUT_EXT),$(OUTS))
 endif
 
 all: $(OUTS)

kernel_module/user/README.adoc

@@ -30,3 +30,7 @@ These programs can also be compiled and used on host.
 .. link:ioctl.c[]
 .. link:netlink.c[]
 .. link:poll.c[]
+. Buildroot libraries
+.. link:eigen.cpp[]
+.. link:openmp.c[]
+.. link:openblas.c[]

kernel_module/user/eigen.cpp

@@ -0,0 +1,14 @@
+/* Official hello world. */
+
+#include <iostream>
+#include <eigen3/Eigen/Dense>
+using Eigen::MatrixXd;
+int main()
+{
+  MatrixXd m(2,2);
+  m(0,0) = 3;
+  m(1,0) = 2.5;
+  m(0,1) = -1;
+  m(1,1) = m(1,0) + m(0,1);
+  std::cout << m << std::endl;
+}