porting

早期freebsd实现

	Preliminary Notes on Porting BFD
	--------------------------------

The 'host' is the system a tool runs *on*.
The 'target' is the system a tool runs *for*, i.e.
a tool can read/write the binaries of the target.

Porting to a new host
---------------------
Pick a name for your host. Call that <host>.
(<host> might be sun4, ...)
Create a file hosts/h-<host>.

Porting to a new target
-----------------------
Pick a name for your target. Call that <target>.
You need to create <target>.c and config/mt-<target>.

config/mt-<target> is a Makefile fragment.
The following usually is enough:
TDEFINES = -DDEFAULT_VECTOR=<target>_vec

The file <target>.c is the hard part.  It implements the
bfd_target <target>_vec, which includes pointers to
functions that do the actual <target>-specific methods.

Porting to a <target> that uses the a.out binary format
-------------------------------------------------------

In this case, the include file aout-target.h probaby does most
of what you need. The program gen-aout generates <target>.c for
you automatically for many a.out systems.  Do:
	make gen-aout
	./gen-aout <target> > <target>.c
(This only works if you are building on the target ("native").
If you must make a cross-portt from scratch, copy  the most
similar existing file that include aout-target.h, and fix what is wrong.)

Check the parameters in <target>.c, and fix anything that is wrong.
(Also let us know about it; perhaps we can improve gen-aout.c.)

TARGET_IS_BIG_ENDIAN_P
	Should be defined if <target> is big-endian.

N_HEADER_IN_TEXT(x)
	See discussion in ../include/aout/aout32.h.

BYTES_IN_WORD
	Number of bytes per word. (Usually 4 but can be 8.)

ARCH
	Number of bits per word.  (Usually 32, but can be 64.)

ENTRY_CAN_BE_ZERO
	Define if the extry point (start address of an
	executable program) can be 0x0.

TEXT_START_ADDR
	The address of the start of the text segemnt in
	virtual memory.  Normally, the same as the entry point.

PAGE_SIZE

SEGMENT_SIZE
	Usually, teh same as the PAGE_SIZE.
	Alignmement needed for the data segment.

TARGETNAME
	The name of the target, for run-time lookups.
	Usually "a.out-<target>"