1 Article 484 of comp.lang.perl:
2 Xref: netlabs comp.lang.perl:484 comp.lang.c:983 alt.sources:134
3 Path: netlabs!psinntp!iggy.GW.Vitalink.COM!lll-winken!sun-barr!cronkite.Central.Sun.COM!spdev!texsun!convex!tchrist
4 From: tchrist@convex.com (Tom Christiansen)
5 Newsgroups: comp.lang.perl,comp.lang.c,alt.sources
6 Subject: pstruct -- a C structure formatter; AKA c2ph, a C to perl header translator
7 Keywords: C perl tranlator
8 Message-ID: <1991Jul25.081021.8104@convex.com>
9 Date: 25 Jul 91 08:10:21 GMT
10 Sender: usenet@convex.com (news access account)
11 Followup-To: comp.lang.perl
12 Organization: CONVEX Computer Corporation, Richardson, Tx., USA
14 Nntp-Posting-Host: pixel.convex.com
16 Once upon a time, I wrote a program called pstruct. It was a perl
17 program that tried to parse out C structures and display their member
18 offsets for you. This was especially useful for people looking at
19 binary dumps or poking around the kernel.
21 Pstruct was not a pretty program. Neither was it particularly robust.
22 The problem, you see, was that the C compiler was much better at parsing
23 C than I could ever hope to be.
25 So I got smart: I decided to be lazy and let the C compiler parse the C,
26 which would spit out debugger stabs for me to read. These were much
27 easier to parse. It's still not a pretty program, but at least it's more
30 Pstruct takes any .c or .h files, or preferably .s ones, since that's
31 the format it is going to massage them into anyway, and spits out
35 int tty.t_locker 000 4
36 int tty.t_mutex_index 004 4
37 struct tty * tty.t_tp_virt 008 4
38 struct clist tty.t_rawq 00c 20
39 int tty.t_rawq.c_cc 00c 4
40 int tty.t_rawq.c_cmax 010 4
41 int tty.t_rawq.c_cfx 014 4
42 int tty.t_rawq.c_clx 018 4
43 struct tty * tty.t_rawq.c_tp_cpu 01c 4
44 struct tty * tty.t_rawq.c_tp_iop 020 4
45 unsigned char * tty.t_rawq.c_buf_cpu 024 4
46 unsigned char * tty.t_rawq.c_buf_iop 028 4
47 struct clist tty.t_canq 02c 20
48 int tty.t_canq.c_cc 02c 4
49 int tty.t_canq.c_cmax 030 4
50 int tty.t_canq.c_cfx 034 4
51 int tty.t_canq.c_clx 038 4
52 struct tty * tty.t_canq.c_tp_cpu 03c 4
53 struct tty * tty.t_canq.c_tp_iop 040 4
54 unsigned char * tty.t_canq.c_buf_cpu 044 4
55 unsigned char * tty.t_canq.c_buf_iop 048 4
56 struct clist tty.t_outq 04c 20
57 int tty.t_outq.c_cc 04c 4
58 int tty.t_outq.c_cmax 050 4
59 int tty.t_outq.c_cfx 054 4
60 int tty.t_outq.c_clx 058 4
61 struct tty * tty.t_outq.c_tp_cpu 05c 4
62 struct tty * tty.t_outq.c_tp_iop 060 4
63 unsigned char * tty.t_outq.c_buf_cpu 064 4
64 unsigned char * tty.t_outq.c_buf_iop 068 4
65 (*int)() tty.t_oproc_cpu 06c 4
66 (*int)() tty.t_oproc_iop 070 4
67 (*int)() tty.t_stopproc_cpu 074 4
68 (*int)() tty.t_stopproc_iop 078 4
69 struct thread * tty.t_rsel 07c 4
74 Actually, this was generated by a particular set of options. You can control
75 the formatting of each column, whether you prefer wide or fat, hex or decimal,
76 leading zeroes or whatever.
78 All you need to be able to use this is a C compiler than generates
79 BSD/GCC-style stabs. The -g option on native BSD compilers and GCC
80 should get this for you.
82 To learn more, just type a bogus option, like -\?, and a long usage message
83 will be provided. There are a fair number of possibilities.
85 If you're only a C programmer, than this is the end of the message for you.
86 You can quit right now, and if you care to, save off the source and run it
87 when you feel like it. Or not.
91 But if you're a perl programmer, then for you I have something much more
92 wondrous than just a structure offset printer.
94 You see, if you call pstruct by its other incybernation, c2ph, you have a code
95 generator that translates C code into perl code! Well, structure and union
96 declarations at least, but that's quite a bit.
98 Prior to this point, anyone programming in perl who wanted to interact
99 with C programs, like the kernel, was forced to guess the layouts of the C
100 strutures, and then hardwire these into his program. Of course, when you
101 took your wonderfully to a system where the sgtty structure was laid out
102 differently, you program broke. Which is a shame.
104 We've had Larry's h2ph translator, which helped, but that only works on
105 cpp symbols, not real C, which was also very much needed. What I offer
106 you is a symbolic way of getting at all the C structures. I've couched
107 them in terms of packages and functions. Consider the following program:
109 #!/usr/local/bin/perl
111 require 'syscall.ph';
112 require 'sys/time.ph';
113 require 'sys/resource.ph';
115 $ru = "\0" x &rusage'sizeof();
117 syscall(&SYS_getrusage, &RUSAGE_SELF, $ru) && die "getrusage: $!";
119 @ru = unpack($t = &rusage'typedef(), $ru);
121 $utime = $ru[ &rusage'ru_utime + &timeval'tv_sec ]
122 + ($ru[ &rusage'ru_utime + &timeval'tv_usec ]) / 1e6;
124 $stime = $ru[ &rusage'ru_stime + &timeval'tv_sec ]
125 + ($ru[ &rusage'ru_stime + &timeval'tv_usec ]) / 1e6;
127 printf "you have used %8.3fs+%8.3fu seconds.\n", $utime, $stime;
130 As you see, the name of the package is the name of the structure. Regular
131 fields are just their own names. Plus the follwoing accessor functions are
132 provided for your convenience:
134 struct This takes no arguments, and is merely the number of first-level
135 elements in the structure. You would use this for indexing
136 into arrays of structures, perhaps like this
139 $usec = $u[ &user'u_utimer
140 + (&ITIMER_VIRTUAL * &itimerval'struct)
141 + &itimerval'it_value
145 sizeof Returns the bytes in the structure, or the member if
146 you pass it an argument, such as
148 &rusage'sizeof(&rusage'ru_utime)
150 typedef This is the perl format definition for passing to pack and
151 unpack. If you ask for the typedef of a nothing, you get
152 the whole structure, otherwise you get that of the member
153 you ask for. Padding is taken care of, as is the magic to
154 guarantee that a union is unpacked into all its aliases.
155 Bitfields are not quite yet supported however.
157 offsetof This function is the byte offset into the array of that
158 member. You may wish to use this for indexing directly
159 into the packed structure with vec() if you're too lazy
162 typeof Not to be confused with the typedef accessor function, this
163 one returns the C type of that field. This would allow
164 you to print out a nice structured pretty print of some
165 structure without knoning anything about it beforehand.
166 No args to this one is a noop. Someday I'll post such
167 a thing to dump out your u structure for you.
170 The way I see this being used is like basically this:
172 % h2ph <some_include_file.h > /usr/lib/perl/tmp.ph
173 % c2ph some_include_file.h >> /usr/lib/perl/tmp.ph
176 It's a little tricker with c2ph because you have to get the includes right.
177 I can't know this for your system, but it's not usually too terribly difficult.
179 The code isn't pretty as I mentioned -- I never thought it would be a 1000-
180 line program when I started, or I might not have begun. :-) But I would have
181 been less cavalier in how the parts of the program communicated with each
182 other, etc. It might also have helped if I didn't have to divine the makeup
183 of the stabs on the fly, and then account for micro differences between my
186 Anyway, here it is. Should run on perl v4 or greater. Maybe less.