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1.1 root 1: .\"
2: .\" Readme 4.1 82/05/12
3: .\"
4: .sp
5: .ce 100
6: A Package to Support VAX Compatability Mode on UNIX-32V
7: .sp
8: Arthur W. Wetzel
9: .br
10: 735 LIS Bldg
11: .br
12: Interdisciplinary Department of Information Science
13: .br
14: University of Pittsburgh
15: .br
16: Pittsburgh, Pa. 15260
17: (412)-624-5203
18: .ce 0
19: .sp 2
20: This is a brief description of a
21: package to support the execution of PDP-11 programs on
22: VAX UNIX-32V
23: or Berkeley VMUNIX
24: in compatability mode.
25: The major functions are to
26: .in +5
27: .sp
28: .ti -5
29: 1) allocate a block
30: of memory as the PDP-11 memory space (this must start at location 0),
31: .ti -5
32: 2) read compatability
33: mode program images into memory and lay them out properly (with arguments etc),
34: .ti -5
35: 3) actually handle the change to and from compatability mode,
36: .ti -5
37: 4) simulate system calls for what ever operating system is being simulated
38: and
39: .ti -5
40: 5) simulate floating point (FPU and FIS) instructions.
41: .sp
42: .in -5
43: Unfortunately programs requiring separated I/D space can not be run.
44: Loading of the package is rather slow since the entire process is about
45: 80K bytes
46: (64K is the PDP-11 space).
47: Once execution begins however, the speed is similar to a PDP-11/70.
48: There is considerable overhead for each exception condition
49: so that programs with a lot of system calls or especially with
50: floating point will be greatly slowed down.
51: Note that the text segment must be writable since the PDP-11
52: memory space is there.
53: .sp
54: Three quick changes to UNIX-32V and Berkeley VMUNIX
55: were made in the course of constructing this package.
56: .in 5
57: .sp
58: .ti -5
59: First, it is necessary to patch a bug in the original mchdep.c.
60: The bug in the sendsig routine is that the condition codes are masked out
61: of the psl before it is stacked when catching signals.
62: This affects all
63: programs not just compatability mode ones although is is not usually a frequent
64: problem execept in this application.
65: The mask which was 0xfff1
66: should be changed to 0xffff.
67: If this is not done, the condition codes
68: after a signal trap routine returns will always be cleared which can result
69: in many strange problems when condition codes are being checked in loops
70: or in this case after an "illegal instruction" trap.
71: This same bug remains in the
72: Third Berkeley Software Tape version of Virtual Memory UNIX.
73: .sp
74: .ti -5
75: Second, although it is easy to get into compatability mode one also
76: needs a way to get back when an exception condition arises.
77: This can be done
78: by changing another mask in the last line of the same routine.
79: The 0x1f
80: mask should be changed to 0x8000001f.
81: This clears the compatability mode bit
82: so that all signals are necessarily caught in native mode where native code
83: can do something about the situation.
84: .sp
85: .ti -5
86: Finally, if one wants compatibility
87: mode programs to have SETUID and SETGID status, there must be a way to change
88: the effective uid or gid without clobbering the real uid or gid.
89: This is
90: easily done by adding seteuid and setegid system calls to UNIX-32V.
91: My method
92: of doing this was to modify setuid and getuid so that the high order 16 bits
93: of the argument in the actual system calls is a flag (uids and gids are only
94: 16 bits in the low order part of the word) to indicate either a regular
95: setuid or getuid function or alternately a seteuid and setegid function.
96: Appropriate functions seteuid() and setegid() have been added to our libc.a
97: which automatically set up the flags while setuid() and setgid() insure
98: that the flags are zeroed.
99: .in -5
100: .sp
101: Most of the programming was done in late August 1979 with additions being made
102: occasionally thru August 1980.
103: Compilation procedures are specified in Makefile.
104: An effort was made to minimize the amount of assembly language coding
105: so that only two small assembler routines are found here.
106: One of these (memsiz.s) simply specifies
107: how much memory is being allocated for PDP-11 images
108: and makes it available through certain global variables.
109: The other assembler file (compat.s) handles the protocol for getting
110: into compatability mode at a certain pc and with a certain ps.
111: It also includes a getreg function which copies machine registers into
112: known places.
113: The heart of the entire package is runcompat.c which is used for all RTSs
114: (Run Time Systems).
115: The function main here simply checks for the existence of the
116: file to be executed and sets the required uid and gid.
117: The execute function actually copies the file to memory
118: and sets trap conditions.
119: Finally illtrap() catches illegal instructions and goes to the
120: code appropriate for what is found as the illegal instruction.
121: The bulk of the lines of C code are in unixtraps.c and dofloat.c
122: which do UNIX system calls in either version 6 or 7 format
123: and simulate floating point operations.
124: (Since PWB-UNIX is upward compatable with version 6, the version 6
125: system support also includes PWB sys calls.)
126: There are probably a number of bugs in the floating point simulation
127: code just waiting to be found.
128: If you are running programs which already include the PDP-11
129: floating point interpretation code, you may want to disable
130: dofloat as the illegal instructions can be caught and simulated
131: in the PDP-11 code.
132: To do this just make dofloat.o with "cc -c -O -DNOFPSIM dofloat.c".
133: .sp
134: A shell which will automatically invoke compatability mode programs
135: is in the modshell directory as difference listings from the original
136: UNIX-32V shell.
137: Most of the new code is in a new function compat.c.
138: The automatic recognition of PDP-11 UNIX version 6/7 programs
139: relies on the fact that the second word (16 bit) of a PDP-11
140: a.out file (text size) is nonzero whereas it is 0 for 32V a.outs.
141: No easy distinction can be made between version 6 and version 7 a.outs
142: so that a shell variable RTS sets up the name of a default Run
143: Time System.
144: On our system version 6 a.outs have been patched so that word 6 of the header
145: which is unused is a 1.
146: This hoaky? method seems to work just fine.
147: A program v6flag.c is in the modshell directory to do this.
148: .sp
149: One possible use of this package is to get programs like INGRES running
150: on the VAX without going through what appears to be a nontrivial
151: conversion effort.
152: There are two ways of running such programs.
153: Firstly if the shell is patched to automatically recognize and
154: run compatability mode a.outs (as in modshell), the PDP-11 a.out files
155: for the program can be just put on the system with their
156: normal names and run as usual.
157: Note however that you will be using the UNIX-32V shell so that
158: any shell files from PDP-11 version 6 will have to be modified
159: for this to work correctly with something like INGRES.
160: The second approach
161: is to make a directory hierarchy somewhere which corresponds
162: to what would be on a PDP-11 including the appropriate PDP-11 shell.
163: In that case just execute that shell in compatability mode with
164: the root directory set to the top of the PDP-11 hierarchy.
165: This is the quickest way to get something going in a hurry since no
166: changes are required to existing PDP-11 code or shell files.
167: .sp
168: Emulation of RT-11 system calls provided by Dan Strick are not being
169: distributed at this time.
170: .sp
171: Please foreward any comments, bug fixes or quick questions to the author
172: at the above address.
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