How is the CPU symbol resolved in this C sample code?

Question

I ran into the following code in location.c for the apache jsvc java daemon.

char *location_jvm_cfg[] = {
    "$JAVA_HOME/jre/lib/jvm.cfg",           /* JDK */
    "$JAVA_HOME/lib/jvm.cfg",               /* JRE */
    "$JAVA_HOME/jre/lib/" CPU "/jvm.cfg",   /* JDK */
    "$JAVA_HOME/lib/" CPU "/jvm.cfg",       /* JRE */
    NULL,
};

I grepped through the source code to find out the CPU macro is expanded in the code "$JAVA_HOME/jre/lib/" CPU "/jvm.cfg" but could not find such a MACRO defined.

I am not really sure if CPU is a C Macro or some other thing that is being configured the autoconf tools.

how is the above CPU value being substituted for the real CPU value?

The problem I am facing is that when I build jsvc on Solaris with CFLAGS and LDFLAGS set to -m64 the generated 64 bit solaris binary tries to load the jvm .so files from $JAVA_HOME/jre/lib/sparc/jvm.cfg instead of $JAVA_HOME/jre/lib/sparcv9/jvm.cfg

UPDATE

Running ./configure that ships with JSVC with the following command line does the right thing

configure --with-java=/path/to/jdk1.7.0_45 --host=sparcv9-sun-solaris2.10 CFLAGS="-m64" LDFLAGS="-m64"

the extra --host=sparcv9-sun-solaris2.10 causes the generated gcc command to be

gcc -m64 -DOS_SOLARIS -DDSO_DLFCN -DCPU=\"sparcv9\" -Wall -Wstrict-prototypes

Instead of

gcc -m64 -DOS_SOLARIS -DDSO_DLFCN -DCPU=\"sparc\" -Wall -Wstrict-prototypes

which is what was causing the generated 64 bit jsvc binary to try to link against the 32 bit so files instead of the 64 bit so files.

Answer 1

It absolutely must be a preprocessor define. Nothing else would work in that code.

For making configure use different CPUs, it may be possible that the configure script takes a configuration triplet. That might look like 'i686-unknown-gnu-linux'

Apparently configure.guess does the work of figuring this out. If you specify one of these triplets (quadruplets?) on the configure command line it might think it is building in a cross-compiler, but it should work.

Answer 2

The generated configure script adds -DCPU to CFLAGS, based on the value of configure --host, which defaults to configure --build, which defaults to a guessed value.