$NetBSD: README,v 1.5 2009/12/13 17:58:27 snj Exp $


Building multi- ABI libraries for NetBSD platforms.


src/compat has a framework to (re)build the libraries shipped with
NetBSD for a different ABI than the default for that platform.  This
allows 32-bit libraries for the amd64 and sparc64 ports, and enables
the mips64 port to support all three of old-style 32-bit ("o32"), the
new 32-bit (default, "n32", 64-bit CPU required) or the 64-bit ABI.


The basic premise is to re-set $MAKEOBJDIRPREFIX to fresh subdirectory
underneath src/compat and rebuild the libraries with a different set
of options.  Each platform wanting support should create their port
subdirectory directly in src/compat, and then one subdirectory in here
for each ABI required.  e.g., src/compat/amd64/i386 is where we build
the 32-bit compat libraries for the amd64 port.  In each of these
subdirs, a small Makefile and makefile fragment should exist.  The
Makefile should set BSD_MK_COMPAT_FILE to equal the fragment, and then
include "../../Makefile.common".  Eg, amd64/i386/Makefile has:

	BSD_MK_COMPAT_FILE=${.CURDIR}/bsd.i386.mk

	.include "../../Makefile.common"

In the makefile fragment any changes to ABI flags are passed here
and the MLIBDIR variable must be set to the subdirectory in /usr/lib
where libraries for the ABI will be installed.  There are a couple of
helper Makefiles around.  amd64/i386/bsd.i386.mk looks like:

	LD+=			-m elf_i386
	MLIBDIR=		i386
	LIBC_MACHINE_ARCH=	${MLIBDIR}
	COMMON_MACHINE_ARCH=	${MLIBDIR}
	KVM_MACHINE_ARCH=	${MLIBDIR}
	PTHREAD_MACHINE_ARCH=	${MLIBDIR}
	BFD_MACHINE_ARCH=	${MLIBDIR}
	CSU_MACHINE_ARCH=	${MLIBDIR}
	CRYPTO_MACHINE_CPU=	${MLIBDIR}
	LDELFSO_MACHINE_CPU=	${MLIBDIR}

	.include "${NETBSDSRCDIR}/compat/Makefile.m32"

and the referenced Makefile.m32 looks like:

	COPTS+=			-m32
	CPUFLAGS+=		-m32
	LDADD+=			-m32
	LDFLAGS+=		-m32
	MKDEPFLAGS+=		-m32

	.include "Makefile.compat"


Makefile.common holds the list of subdirectories (the libraries and
ld.elf_so) to build with this ABI.

Makefile.md_subdir holds the list of subdirectories for each port.

Makefile.compat has the basic framework to force the right paths for
library and ld.elf_so linkage.  It contains a hack to create subdirs
in the build that should be fixed.

dirshack/Makefile is a hack to get objdirs created timely, and should
be fixed in a better way.



mrg@eterna.com.au
december 2009