eigen: add hello world

Mention openmp on readme

README.adoc

@@ -4164,7 +4164,6 @@ Buildroot built-in libraries, mostly under Libraries > Other:
 
 * Armadillo `C++`: linear algebra
 * fftw: Fourier transform
-* Eigen: linear algebra
 * Flann
 * GSL: various
 * liblinear
@@ -4174,21 +4173,21 @@ Buildroot built-in libraries, mostly under Libraries > Other:
 
 There are not yet enabled, but it should be easy to so, see: <<add-new-buildroot-packages>>
 
+===== OpenMP
+
+Implemented by GCC itself, so just a toolchain configuration, no external libs, and we enable it by default:
+
+....
+/openmp.out
+....
+
 ===== BLAS
 
 Buildroot supports it, which makes everything just trivial:
 
 ....
-./build \
+./build -a arm -B 'BR2_PACKAGE_OPENBLAS=y' -k
-  -a arm \
+./run -F '/openblas.out'
-  -B 'BR2_PACKAGE_OPENBLAS=y' \
-;
-....
-
-and then inside the guest run our test program:
-
-....
-/openblas.out
 ....
 
 For x86, you also need:
@@ -4203,6 +4202,15 @@ to overcome this bug: https://bugs.busybox.net/show_bug.cgi?id=10856
 sgemm_kernel.o: No such file or directory
 ....
 
+===== Eigen
+
+Header only linear algebra library supported by Buildroot:
+
+....
+./build -B 'BR2_PACKAGE_EIGEN=y' -k
+./run -F '/eigen.out'
+....
+
 ===== PARSEC benchmark
 
 We have ported parts of the link:http://parsec.cs.princeton.edu[PARSEC benchmark] for cross compilation at: https://github.com/cirosantilli/parsec-benchmark See the documentation on that repo to find out which benchmarks have been ported. Some of the benchmarks were are segfaulting, they are documented in that repo.

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;
+}