ax.h revision 1.7 
1/* Definitions for expressions designed to be executed on the agent
2   Copyright (C) 1998-2017 Free Software Foundation, Inc.
3
4   This file is part of GDB.
5
6   This program is free software; you can redistribute it and/or modify
7   it under the terms of the GNU General Public License as published by
8   the Free Software Foundation; either version 3 of the License, or
9   (at your option) any later version.
10
11   This program is distributed in the hope that it will be useful,
12   but WITHOUT ANY WARRANTY; without even the implied warranty of
13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14   GNU General Public License for more details.
15
16   You should have received a copy of the GNU General Public License
17   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
18
19#ifndef AGENTEXPR_H
20#define AGENTEXPR_H
21
22#include "doublest.h"		/* For DOUBLEST.  */
23#include "vec.h"
24
25/* It's sometimes useful to be able to debug programs that you can't
26   really stop for more than a fraction of a second.  To this end, the
27   user can specify a tracepoint (like a breakpoint, but you don't
28   stop at it), and specify a bunch of expressions to record the
29   values of when that tracepoint is reached.  As the program runs,
30   GDB collects the values.  At any point (possibly while values are
31   still being collected), the user can display the collected values.
32
33   This is used with remote debugging; we don't really support it on
34   native configurations.
35
36   This means that expressions are being evaluated by the remote agent,
37   which doesn't have any access to the symbol table information, and
38   needs to be small and simple.
39
40   The agent_expr routines and datatypes are a bytecode language
41   designed to be executed by the agent.  Agent expressions work in
42   terms of fixed-width values, operators, memory references, and
43   register references.  You can evaluate a agent expression just given
44   a bunch of memory and register values to sniff at; you don't need
45   any symbolic information like variable names, types, etc.
46
47   GDB translates source expressions, whose meaning depends on
48   symbolic information, into agent bytecode expressions, whose meaning
49   is independent of symbolic information.  This means the agent can
50   evaluate them on the fly without reference to data only available
51   to the host GDB.  */
52
53
54/* Different kinds of flaws an agent expression might have, as
55   detected by ax_reqs.  */
56enum agent_flaws
57  {
58    agent_flaw_none = 0,	/* code is good */
59
60    /* There is an invalid instruction in the stream.  */
61    agent_flaw_bad_instruction,
62
63    /* There is an incomplete instruction at the end of the expression.  */
64    agent_flaw_incomplete_instruction,
65
66    /* ax_reqs was unable to prove that every jump target is to a
67       valid offset.  Valid offsets are within the bounds of the
68       expression, and to a valid instruction boundary.  */
69    agent_flaw_bad_jump,
70
71    /* ax_reqs was unable to prove to its satisfaction that, for each
72       jump target location, the stack will have the same height whether
73       that location is reached via a jump or by straight execution.  */
74    agent_flaw_height_mismatch,
75
76    /* ax_reqs was unable to prove that every instruction following
77       an unconditional jump was the target of some other jump.  */
78    agent_flaw_hole
79  };
80
81/* Agent expression data structures.  */
82
83/* The type of an element of the agent expression stack.
84   The bytecode operation indicates which element we should access;
85   the value itself has no typing information.  GDB generates all
86   bytecode streams, so we don't have to worry about type errors.  */
87
88union agent_val
89  {
90    LONGEST l;
91    DOUBLEST d;
92  };
93
94/* A buffer containing a agent expression.  */
95struct agent_expr
96  {
97    /* Construct an empty agent expression.  */
98    explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope);
99
100    ~agent_expr ();
101
102    /* The bytes of the expression.  */
103    unsigned char *buf;
104
105    /* The number of bytecode in the expression.  */
106    int len;
107
108    /* Allocated space available currently.  */
109    int size;
110
111    /* The target architecture assumed to be in effect.  */
112    struct gdbarch *gdbarch;
113
114    /* The address to which the expression applies.  */
115    CORE_ADDR scope;
116
117    /* If the following is not equal to agent_flaw_none, the rest of the
118       information in this structure is suspect.  */
119    enum agent_flaws flaw;
120
121    /* Number of elements left on stack at end; may be negative if expr
122       only consumes elements.  */
123    int final_height;
124
125    /* Maximum and minimum stack height, relative to initial height.  */
126    int max_height, min_height;
127
128    /* Largest `ref' or `const' opcode used, in bits.  Zero means the
129       expression has no such instructions.  */
130    int max_data_size;
131
132    /* Bit vector of registers needed.  Register R is needed iff
133
134       reg_mask[R / 8] & (1 << (R % 8))
135
136       is non-zero.  Note!  You may not assume that this bitmask is long
137       enough to hold bits for all the registers of the machine; the
138       agent expression code has no idea how many registers the machine
139       has.  However, the bitmask is reg_mask_len bytes long, so the
140       valid register numbers run from 0 to reg_mask_len * 8 - 1.
141
142       Also note that this mask may contain registers that are needed
143       for the original collection expression to work, but that are
144       not referenced by any bytecode.  This could, for example, occur
145       when collecting a local variable allocated to a register; the
146       compiler sets the mask bit and skips generating a bytecode whose
147       result is going to be discarded anyway.
148    */
149    int reg_mask_len;
150    unsigned char *reg_mask;
151
152    /* For the data tracing facility, we need to insert `trace' bytecodes
153       before each data fetch; this records all the memory that the
154       expression touches in the course of evaluation, so that memory will
155       be available when the user later tries to evaluate the expression
156       in GDB.
157
158       Setting the flag 'tracing' to non-zero enables the code that
159       emits the trace bytecodes at the appropriate points.  */
160
161    unsigned int tracing : 1;
162
163    /* This indicates that pointers to chars should get an added
164       tracenz bytecode to record nonzero bytes, up to a length that
165       is the value of trace_string.  */
166
167    int trace_string;
168  };
169
170/* An agent_expr owning pointer.  */
171typedef std::unique_ptr<agent_expr> agent_expr_up;
172
173/* The actual values of the various bytecode operations.  */
174
175enum agent_op
176  {
177#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
178    aop_ ## NAME = VALUE,
179#include "ax.def"
180#undef DEFOP
181    aop_last
182  };
183
184
185
186/* Functions for building expressions.  */
187
188/* Append a raw byte to EXPR.  */
189extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
190
191/* Append a simple operator OP to EXPR.  */
192extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
193
194/* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
195   with 0 being top of stack.  */
196extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
197
198/* Append the floating-point prefix, for the next bytecode.  */
199#define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
200
201/* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
202extern void ax_ext (struct agent_expr *EXPR, int N);
203
204/* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
205extern void ax_zero_ext (struct agent_expr *EXPR, int N);
206
207/* Append a trace_quick instruction to EXPR, to record N bytes.  */
208extern void ax_trace_quick (struct agent_expr *EXPR, int N);
209
210/* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
211   aop_if_goto).  We assume we don't know the target offset yet,
212   because it's probably a forward branch, so we leave space in EXPR
213   for the target, and return the offset in EXPR of that space, so we
214   can backpatch it once we do know the target offset.  Use ax_label
215   to do the backpatching.  */
216extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
217
218/* Suppose a given call to ax_goto returns some value PATCH.  When you
219   know the offset TARGET that goto should jump to, call
220   ax_label (EXPR, PATCH, TARGET)
221   to patch TARGET into the ax_goto instruction.  */
222extern void ax_label (struct agent_expr *EXPR, int patch, int target);
223
224/* Assemble code to push a constant on the stack.  */
225extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
226extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
227
228/* Assemble code to push the value of register number REG on the
229   stack.  */
230extern void ax_reg (struct agent_expr *EXPR, int REG);
231
232/* Add the given register to the register mask of the expression.  */
233extern void ax_reg_mask (struct agent_expr *ax, int reg);
234
235/* Assemble code to operate on a trace state variable.  */
236extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
237
238/* Append a string to the bytecode stream.  */
239extern void ax_string (struct agent_expr *x, const char *str, int slen);
240
241
242/* Functions for printing out expressions, and otherwise debugging
243   things.  */
244
245/* Disassemble the expression EXPR, writing to F.  */
246extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
247
248/* An entry in the opcode map.  */
249struct aop_map
250  {
251
252    /* The name of the opcode.  Null means that this entry is not a
253       valid opcode --- a hole in the opcode space.  */
254    const char *name;
255
256    /* All opcodes take no operands from the bytecode stream, or take
257       unsigned integers of various sizes.  If this is a positive number
258       n, then the opcode is followed by an n-byte operand, which should
259       be printed as an unsigned integer.  If this is zero, then the
260       opcode takes no operands from the bytecode stream.
261
262       If we get more complicated opcodes in the future, don't add other
263       magic values of this; that's a crock.  Add an `enum encoding'
264       field to this, or something like that.  */
265    int op_size;
266
267    /* The size of the data operated upon, in bits, for bytecodes that
268       care about that (ref and const).  Zero for all others.  */
269    int data_size;
270
271    /* Number of stack elements consumed, and number produced.  */
272    int consumed, produced;
273  };
274
275/* Map of the bytecodes, indexed by bytecode number.  */
276extern struct aop_map aop_map[];
277
278/* Given an agent expression AX, analyze and update its requirements.  */
279
280extern void ax_reqs (struct agent_expr *ax);
281
282#endif /* AGENTEXPR_H */
283