Spoofing an RPM's host name

# This spoofs the build host for both 32- and 64-bit applications

# To use:
# 1. Add libmyhostname as a target that calls rpmbuild
# 2. Add "myhostnameclean" as a target to your "clean"
# 3. Call rpmbuild or any other program with $(SPOOF_HOSTNAME) prefix

MYHOSTNAME_MNAME:=$(shell uname -m)
libmyhostname:=libmyhostname_$(MYHOSTNAME_MNAME).so
MYHOSTNAME_PWD:=$(shell pwd)
SPOOF_HOSTNAME:=LD_PRELOAD=$(MYHOSTNAME_PWD)/myhostname/\$$LIB/$(libmyhostname)

.PHONY: myhostnameclean
.SILENT: myhostnameclean
.IGNORE: myhostnameclean
myhostnameclean:
        rm -rf myhostname

# Linux doesn't support explicit 32- vs. 64-bit LD paths like Solaris, but ld.so
# does accept a literal "$LIB" in the path to expand to lib vs lib64. So we need
# to make our own private library tree myhostname/lib{,64} to feed to rpmbuild.
.PHONY: libmyhostname
.SILENT: libmyhostname
libmyhostname: /usr/include/gnu/stubs-32.h /lib/libgcc_s.so.1
        mkdir -p myhostname/lib{,64}
        $(MAKE) -I $(MYHOSTNAME_PWD) -s --no-print-directory -C myhostname/lib   -f $(MYHOSTNAME_PWD)/Makefile $(libmyhostname) MYHOSTARCH=32
        $(MAKE) -I $(MYHOSTNAME_PWD) -s --no-print-directory -C myhostname/lib64 -f $(MYHOSTNAME_PWD)/Makefile $(libmyhostname) MYHOSTARCH=64

.SILENT: /usr/include/gnu/stubs-32.h /lib/libgcc_s.so.1
/usr/include/gnu/stubs-32.h:
        echo "You need to install the 'glibc-devel.i686' package."
        echo "'sudo yum install glibc-devel.i686' should do it for you."
        false

/lib/libgcc_s.so.1:
        echo "You need to install the 'libgcc.i686' package."
        echo "'sudo yum install libgcc.i686' should do it for you."
        false

.SILENT: libmyhostname $(libmyhostname) libmyhostname_$(MYHOSTNAME_MNAME).o libmyhostname_$(MYHOSTNAME_MNAME).c
$(libmyhostname): libmyhostname_$(MYHOSTNAME_MNAME).o
        echo "Building $(MYHOSTARCH)-bit version of hostname spoofing library."
        gcc -m$(MYHOSTARCH) -shared -o $@ $<

libmyhostname_$(MYHOSTNAME_MNAME).o: libmyhostname_$(MYHOSTNAME_MNAME).c
        gcc -m$(MYHOSTARCH) -fPIC -rdynamic -g -c -Wall $<

libmyhostname_$(MYHOSTNAME_MNAME).c:
        echo "$$libmyhostname_body" > $@

define libmyhostname_body
#include <string.h>
#include <asm/errno.h>

int gethostname(char *name, size_t len) {
        const char *myhostname = "buildhost_$(MYHOSTNAME_MNAME).myprojectname.proj";
        if (len < strlen(myhostname))
                return(EINVAL);
        strcpy(name, myhostname);
        return(0);
}
endef
export libmyhostname_body