ax.h revision 1.6 
1/* Definitions for expressions designed to be executed on the agent
2   Copyright (C) 1998-2016 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    /* The bytes of the expression.  */
98    unsigned char *buf;
99
100    /* The number of bytecode in the expression.  */
101    int len;
102
103    /* Allocated space available currently.  */
104    int size;
105
106    /* The target architecture assumed to be in effect.  */
107    struct gdbarch *gdbarch;
108
109    /* The address to which the expression applies.  */
110    CORE_ADDR scope;
111
112    /* If the following is not equal to agent_flaw_none, the rest of the
113       information in this structure is suspect.  */
114    enum agent_flaws flaw;
115
116    /* Number of elements left on stack at end; may be negative if expr
117       only consumes elements.  */
118    int final_height;
119
120    /* Maximum and minimum stack height, relative to initial height.  */
121    int max_height, min_height;
122
123    /* Largest `ref' or `const' opcode used, in bits.  Zero means the
124       expression has no such instructions.  */
125    int max_data_size;
126
127    /* Bit vector of registers needed.  Register R is needed iff
128
129       reg_mask[R / 8] & (1 << (R % 8))
130
131       is non-zero.  Note!  You may not assume that this bitmask is long
132       enough to hold bits for all the registers of the machine; the
133       agent expression code has no idea how many registers the machine
134       has.  However, the bitmask is reg_mask_len bytes long, so the
135       valid register numbers run from 0 to reg_mask_len * 8 - 1.
136
137       Also note that this mask may contain registers that are needed
138       for the original collection expression to work, but that are
139       not referenced by any bytecode.  This could, for example, occur
140       when collecting a local variable allocated to a register; the
141       compiler sets the mask bit and skips generating a bytecode whose
142       result is going to be discarded anyway.
143    */
144    int reg_mask_len;
145    unsigned char *reg_mask;
146
147    /* For the data tracing facility, we need to insert `trace' bytecodes
148       before each data fetch; this records all the memory that the
149       expression touches in the course of evaluation, so that memory will
150       be available when the user later tries to evaluate the expression
151       in GDB.
152
153       Setting the flag 'tracing' to non-zero enables the code that
154       emits the trace bytecodes at the appropriate points.  */
155
156    unsigned int tracing : 1;
157
158    /* This indicates that pointers to chars should get an added
159       tracenz bytecode to record nonzero bytes, up to a length that
160       is the value of trace_string.  */
161
162    int trace_string;
163  };
164
165/* Pointer to an agent_expr structure.  */
166typedef struct agent_expr *agent_expr_p;
167
168/* Vector of pointers to agent expressions.  */
169DEF_VEC_P (agent_expr_p);
170
171/* The actual values of the various bytecode operations.  */
172
173enum agent_op
174  {
175#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
176    aop_ ## NAME = VALUE,
177#include "ax.def"
178#undef DEFOP
179    aop_last
180  };
181
182
183
184/* Functions for building expressions.  */
185
186/* Allocate a new, empty agent expression.  */
187extern struct agent_expr *new_agent_expr (struct gdbarch *, CORE_ADDR);
188
189/* Free a agent expression.  */
190extern void free_agent_expr (struct agent_expr *);
191extern struct cleanup *make_cleanup_free_agent_expr (struct agent_expr *);
192
193/* Append a raw byte to EXPR.  */
194extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
195
196/* Append a simple operator OP to EXPR.  */
197extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
198
199/* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
200   with 0 being top of stack.  */
201extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
202
203/* Append the floating-point prefix, for the next bytecode.  */
204#define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
205
206/* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
207extern void ax_ext (struct agent_expr *EXPR, int N);
208
209/* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
210extern void ax_zero_ext (struct agent_expr *EXPR, int N);
211
212/* Append a trace_quick instruction to EXPR, to record N bytes.  */
213extern void ax_trace_quick (struct agent_expr *EXPR, int N);
214
215/* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
216   aop_if_goto).  We assume we don't know the target offset yet,
217   because it's probably a forward branch, so we leave space in EXPR
218   for the target, and return the offset in EXPR of that space, so we
219   can backpatch it once we do know the target offset.  Use ax_label
220   to do the backpatching.  */
221extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
222
223/* Suppose a given call to ax_goto returns some value PATCH.  When you
224   know the offset TARGET that goto should jump to, call
225   ax_label (EXPR, PATCH, TARGET)
226   to patch TARGET into the ax_goto instruction.  */
227extern void ax_label (struct agent_expr *EXPR, int patch, int target);
228
229/* Assemble code to push a constant on the stack.  */
230extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
231extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
232
233/* Assemble code to push the value of register number REG on the
234   stack.  */
235extern void ax_reg (struct agent_expr *EXPR, int REG);
236
237/* Add the given register to the register mask of the expression.  */
238extern void ax_reg_mask (struct agent_expr *ax, int reg);
239
240/* Assemble code to operate on a trace state variable.  */
241extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
242
243/* Append a string to the bytecode stream.  */
244extern void ax_string (struct agent_expr *x, const char *str, int slen);
245
246
247/* Functions for printing out expressions, and otherwise debugging
248   things.  */
249
250/* Disassemble the expression EXPR, writing to F.  */
251extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
252
253/* An entry in the opcode map.  */
254struct aop_map
255  {
256
257    /* The name of the opcode.  Null means that this entry is not a
258       valid opcode --- a hole in the opcode space.  */
259    const char *name;
260
261    /* All opcodes take no operands from the bytecode stream, or take
262       unsigned integers of various sizes.  If this is a positive number
263       n, then the opcode is followed by an n-byte operand, which should
264       be printed as an unsigned integer.  If this is zero, then the
265       opcode takes no operands from the bytecode stream.
266
267       If we get more complicated opcodes in the future, don't add other
268       magic values of this; that's a crock.  Add an `enum encoding'
269       field to this, or something like that.  */
270    int op_size;
271
272    /* The size of the data operated upon, in bits, for bytecodes that
273       care about that (ref and const).  Zero for all others.  */
274    int data_size;
275
276    /* Number of stack elements consumed, and number produced.  */
277    int consumed, produced;
278  };
279
280/* Map of the bytecodes, indexed by bytecode number.  */
281extern struct aop_map aop_map[];
282
283/* Given an agent expression AX, analyze and update its requirements.  */
284
285extern void ax_reqs (struct agent_expr *ax);
286
287#endif /* AGENTEXPR_H */
288