Question

I have a C makefile which generates header file from java code and compiles very simple C executable file. There is an error which I can’t find. When I try to run the code I get UnsatisfiedLinkError.

This is the content of the makefile:

#!/usr/bin/make -f
#
# Makefile for native stuff
#

# c files to compile
C_SOURCES   := sqrt.c

# the name of the library to build
LIBNAME     := sqrt

C_SOURCE_DIR    := src
C_GENSOURCE_DIR := src

TARGET_DIR  := ../../../target
C_BUILD_DIR    = $(TARGET_DIR)/native
JAVA_BUILD_DIR = $(TARGET_DIR)/classes

# the name of the file we build
TARGET      = $(JAVA_BUILD_DIR)/META-INF/lib/$(LIB_PREFIX)$(LIBNAME)$(LIB_EXTN)

# find the jdk. if this doesn't work for you, define JAVA_HOME in your
# environment or on the make command line
JAVA_HOME ?= /opt/jdk1.7.0_02

# classpath for javah
JAVAH_CLASSPATH = `cat $(TARGET_DIR)/compile-classpath`

# tools and options
CFLAGS = -Wall -fpic
CPPFLAGS = -I$(C_SOURCE_DIR) -I$(C_GENSOURCE_DIR) -Iinclude \
    -I$(JAVA_HOME)/include
JAVAH = /opt/jdk1.7.0_02/bin/javah
JAVAH_FLAGS += -classpath $(JAVAH_CLASSPATH)
JAVAH_CMD = $(JAVAH) $(JAVAH_FLAGS) $(OUTPUT_OPTION)
LDFLAGS = -shared
LINK.so = $(CC) $(LDFLAGS) $(LD_LIBS)

ifdef DEBUG
CFLAGS += -g
LDFLAGS += -g
endif

# os-dependent bits
UNAME := $(shell uname)

ifeq ($(UNAME),Linux)
LIB_PREFIX = lib
LIB_EXTN = .so
CPPFLAGS += -I$(JAVA_HOME)/include/linux
else
ifeq ($(findstring CYGWIN,$(UNAME)),CYGWIN)
LIB_PREFIX =
LIB_EXTN = .dll
CPPFLAGS += -I$(JAVA_HOME)/include/win32
else
f := $(error Platform $(UNAME) not supported)
endif
endif

# we look in $(C_SOURCE_DIR) for c files...
vpath %.c $(C_SOURCE_DIR)

# convenience variables
C_OBJFILES = $(addprefix $(C_BUILD_DIR)/,$(subst .c,.o,$(C_SOURCES)))

# default target
all: $(TARGET)

# rule to compile the .c files
$(C_BUILD_DIR)/%.o: %.c
    @mkdir -p `dirname $@`
    $(COMPILE.c) $(OUTPUT_OPTION) $<

# link the C objects into a shared library
$(TARGET): $(C_OBJFILES) $(LDLIBS)
    @mkdir -p `dirname $@`
    $(LINK.so) $(OUTPUT_OPTION) $^

# a rule to build the .h file with javah                    
$(C_GENSOURCE_DIR)/org_DX_57_osgi_NB_27_impl_Sqrt.h: $(JAVA_BUILD_DIR)/org/DX_57/osgi/NB_27/impl/Sqrt.class
    rm -f $@                
    $(JAVAH) $(JAVAH_FLAGS) $(OUTPUT_OPTION) org.DX_57.osgi.NB_27.impl.Sqrt

# the .o file depends on the .h file
$(C_BUILD_DIR)/sqrt.o: $(C_GENSOURCE_DIR)/org_DX_57_osgi_NB_27_impl_Sqrt.h

clean::
    rm -f $(C_OBJFILES)
    rm -f $(TARGET)
    rm -f $(C_BUILD_DIR)/jnirules.mak

Here is the content of the C file:

#include "org_DX_57_osgi_NB_27_impl_Sqrt.h"

JNIEXPORT jdouble JNICALL Java_Sqrt_sqrt
(JNIEnv *env, jclass cls, jdouble d, jdouble tol)
{

    return tol;
}

Best wishes
Peter

Answer 1

UnsatisfiedLinkError means the JVM failed to load the native shared object that the makefile produced, or .so that the native shared object depends on.

Adding absolute path of ../../../target/native to LD_LIBRARY_PATH will enable the JVM to locate the .so. If the .so depends on other .so libraries the directories where these .so exist will also need added to LD_LIBRARY_PATH.

EDIT:

Instead of ../../../target/native use absolute path of NB_27-impl/target/classes/lib.