c2ph

NAME

c2ph, pstruct - Dump C structures as generated from cc -g -S

SYNOPSIS

c2ph [-dpnP] [var=val] [file...]

OPTIONS

-w

Wide; equivalent to type_width=45 member_width=35 offset_width=8

-x

Hex; equivalent to offset_fmt=x offset_width=08 size_fmt=x size_width=04

-n

Do not generate Perl code (default when invoked as pstruct)

-p

Generate Perl code (default when invoked as c2ph)

-v

Generate Perl code, with C declarations as comments

-i

Do not recompute sizes for intrinsic datatypes

-a

Dump information on intrinsics also

-t

Trace execution

-d

Produce large volumes of debugging output

-slist

Give comma-separated list a structures to dump

DESCRIPTION

The following is the old c2ph.doc documentation by Tom Christiansen Date: 25 Jul 91 08:10:21 GMT

Once upon a time, I wrote a program called pstruct. It was a Perl program that tried to parse out C structures and display their member offsets for you. This was especially useful for people looking at binary dumps or poking around the kernel.

Pstruct was not a pretty program. Neither was it particularly robust. The problem, you see, was that the C compiler was much better at parsing C than I could ever hope to be.

So I got smart: I decided to be lazy and let the C compiler parse the C, which would spit out debugger stabs for me to read. These were much easier to parse. It's still not a pretty program, but at least it's more robust.

Pstruct takes any .c or .h files, or preferably .s ones, since that's the format it is going to massage them into anyway, and spits out listings like this:

struct tty {
	int				 tty.t_locker			000	4
	int				 tty.t_mutex_index	 004	4
	struct tty *		tty.t_tp_virt		 008	4
	struct clist		tty.t_rawq			00c	 20
		int				 tty.t_rawq.c_cc		 00c	4
		int				 tty.t_rawq.c_cmax	 010	4
		int				 tty.t_rawq.c_cfx		014	4
		int				 tty.t_rawq.c_clx		018	4
		struct tty *		tty.t_rawq.c_tp_cpu	 01c	4
		struct tty *		tty.t_rawq.c_tp_iop	 020	4
		unsigned char *	 tty.t_rawq.c_buf_cpu	024	4
		unsigned char *	 tty.t_rawq.c_buf_iop	028	4
	struct clist		tty.t_canq			02c	 20
		int				 tty.t_canq.c_cc		 02c	4
		int				 tty.t_canq.c_cmax	 030	4
		int				 tty.t_canq.c_cfx		034	4
		int				 tty.t_canq.c_clx		038	4
		struct tty *		tty.t_canq.c_tp_cpu	 03c	4
		struct tty *		tty.t_canq.c_tp_iop	 040	4
		unsigned char *	 tty.t_canq.c_buf_cpu	044	4
		unsigned char *	 tty.t_canq.c_buf_iop	048	4
	struct clist		tty.t_outq			04c	 20
		int				 tty.t_outq.c_cc		 04c	4
		int				 tty.t_outq.c_cmax	 050	4
		int				 tty.t_outq.c_cfx		054	4
		int				 tty.t_outq.c_clx		058	4
		struct tty *		tty.t_outq.c_tp_cpu	 05c	4
		struct tty *		tty.t_outq.c_tp_iop	 060	4
		unsigned char *	 tty.t_outq.c_buf_cpu	064	4
		unsigned char *	 tty.t_outq.c_buf_iop	068	4
	(*int)()			tty.t_oproc_cpu		 06c	4
	(*int)()			tty.t_oproc_iop		 070	4
	(*int)()			tty.t_stopproc_cpu	074	4
	(*int)()			tty.t_stopproc_iop	078	4
	struct thread *	 tty.t_rsel			07c	4

etc.

Actually, this was generated by a particular set of options. You can control the formatting of each column, whether you prefer wide or fat, hex or decimal, leading zeroes or whatever.

All you need to be able to use this is a C compiler than generates BSD/GCC-style stabs. The -g option on native BSD compilers and GCC should get this for you.

To learn more, just type a bogus option, like -\?, and a long usage message will be provided. There are a fair number of possibilities.

If you're only a C programmer, than this is the end of the message for you. You can quit right now, and if you care to, save off the source and run it when you feel like it. Or not.

But if you're a Perl programmer, then for you I have something much more wondrous than just a structure offset printer.

You see, if you call pstruct by its other incybernation, c2ph, you have a code generator that translates C code into Perl code! Well, structure and union declarations at least, but that's quite a bit.

Prior to this point, anyone programming in Perl who wanted to interact with C programs, like the kernel, was forced to guess the layouts of the C structures, and then hardwire these into his program. Of course, when you took your wonderfully crafted program to a system where the sgtty structure was laid out differently, you program broke. Which is a shame.

We've had Larry's h2ph(1) translator, which helped, but that only works on cpp(1) symbols, not real C, which was also very much needed. What I offer you is a symbolic way of getting at all the C structures. I've couched them in terms of packages and functions. Consider the following program:

#!/usr/local/bin/perl

require 'syscall.ph';
require 'sys/time.ph';
require 'sys/resource.ph';

$ru = "\0" x &rusage'sizeof();

syscall(&SYS_getrusage, &RUSAGE_SELF, $ru)	&& die "getrusage: $!";

@ru = unpack($t = &rusage'typedef(), $ru);

$utime =  $ru[ &rusage'ru_utime + &timeval'tv_sec  ]
	 + ($ru[ &rusage'ru_utime + &timeval'tv_usec ]) / 1e6;

$stime =  $ru[ &rusage'ru_stime + &timeval'tv_sec  ]
	 + ($ru[ &rusage'ru_stime + &timeval'tv_usec ]) / 1e6;

printf "you have used %8.3fs+%8.3fu seconds.\n", $utime, $stime;

As you see, the name of the package is the name of the structure. Regular fields are just their own names. Plus the following accessor functions are provided for your convenience:

struct

This takes no arguments, and is merely the number of first-level elements in the structure. You would use this for indexing into arrays of structures, perhaps like this:

$usec = $u[ &user'u_utimer
			+ (&ITIMER_VIRTUAL * &itimerval'struct)
			+ &itimerval'it_value
			+ &timeval'tv_usec
		];

sizeof

Returns the bytes in the structure, or the member if you pass it an argument, such as

&rusage'sizeof(&rusage'ru_utime)

typedef

This is the Perl format definition for passing to pack and unpack. If you ask for the typedef of a nothing, you get the whole structure, otherwise you get that of the member you ask for. Padding is taken care of, as is the magic to guarantee that a union is unpacked into all its aliases. Bitfields are not quite yet supported however.

offsetof

This function is the byte offset into the array of that member. You may wish to use this for indexing directly into the packed structure with vec() if you're too lazy to unpack it.

typeof

Not to be confused with the typedef accessor function, this one returns the C type of that field. This would allow you to print out a nice structured pretty print of some structure without knowing anything about it beforehand. No args to this one is a noop. Someday I'll post such a thing to dump out your u structure for you.

The way I see this being used is like basically this:

% h2ph <some_include_file.h  >  /usr/lib/perl/tmp.ph
% c2ph  some_include_file.h  >> /usr/lib/perl/tmp.ph
% install

It's a little tricker with c2ph because you have to get the includes right. I can't know this for your system, but it's not usually too terribly difficult.

The code isn't pretty as I mentioned — I never thought it would be a 1000-line program when I started, or I might not have begun. :-) But I would have been less cavalier in how the parts of the program communicated with each other, etc. It might also have helped if I didn't have to divine the makeup of the stabs on the fly, and then account for micro differences between my compiler and gcc(1).

Anyway, here it is. Should run on Perl v4 or greater.

Maybe less.

—tom