ax.h revision 1.8 
1/* Definitions for expressions designed to be executed on the agent
2   Copyright (C) 1998-2019 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 AX_H
20#define AX_H
21
22#include "common/vec.h"
23
24/* It's sometimes useful to be able to debug programs that you can't
25   really stop for more than a fraction of a second.  To this end, the
26   user can specify a tracepoint (like a breakpoint, but you don't
27   stop at it), and specify a bunch of expressions to record the
28   values of when that tracepoint is reached.  As the program runs,
29   GDB collects the values.  At any point (possibly while values are
30   still being collected), the user can display the collected values.
31
32   This is used with remote debugging; we don't really support it on
33   native configurations.
34
35   This means that expressions are being evaluated by the remote agent,
36   which doesn't have any access to the symbol table information, and
37   needs to be small and simple.
38
39   The agent_expr routines and datatypes are a bytecode language
40   designed to be executed by the agent.  Agent expressions work in
41   terms of fixed-width values, operators, memory references, and
42   register references.  You can evaluate a agent expression just given
43   a bunch of memory and register values to sniff at; you don't need
44   any symbolic information like variable names, types, etc.
45
46   GDB translates source expressions, whose meaning depends on
47   symbolic information, into agent bytecode expressions, whose meaning
48   is independent of symbolic information.  This means the agent can
49   evaluate them on the fly without reference to data only available
50   to the host GDB.  */
51
52
53/* Different kinds of flaws an agent expression might have, as
54   detected by ax_reqs.  */
55enum agent_flaws
56  {
57    agent_flaw_none = 0,	/* code is good */
58
59    /* There is an invalid instruction in the stream.  */
60    agent_flaw_bad_instruction,
61
62    /* There is an incomplete instruction at the end of the expression.  */
63    agent_flaw_incomplete_instruction,
64
65    /* ax_reqs was unable to prove that every jump target is to a
66       valid offset.  Valid offsets are within the bounds of the
67       expression, and to a valid instruction boundary.  */
68    agent_flaw_bad_jump,
69
70    /* ax_reqs was unable to prove to its satisfaction that, for each
71       jump target location, the stack will have the same height whether
72       that location is reached via a jump or by straight execution.  */
73    agent_flaw_height_mismatch,
74
75    /* ax_reqs was unable to prove that every instruction following
76       an unconditional jump was the target of some other jump.  */
77    agent_flaw_hole
78  };
79
80/* Agent expression data structures.  */
81
82/* A buffer containing a agent expression.  */
83struct agent_expr
84  {
85    /* Construct an empty agent expression.  */
86    explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope);
87
88    ~agent_expr ();
89
90    /* The bytes of the expression.  */
91    unsigned char *buf;
92
93    /* The number of bytecode in the expression.  */
94    int len;
95
96    /* Allocated space available currently.  */
97    int size;
98
99    /* The target architecture assumed to be in effect.  */
100    struct gdbarch *gdbarch;
101
102    /* The address to which the expression applies.  */
103    CORE_ADDR scope;
104
105    /* If the following is not equal to agent_flaw_none, the rest of the
106       information in this structure is suspect.  */
107    enum agent_flaws flaw;
108
109    /* Number of elements left on stack at end; may be negative if expr
110       only consumes elements.  */
111    int final_height;
112
113    /* Maximum and minimum stack height, relative to initial height.  */
114    int max_height, min_height;
115
116    /* Largest `ref' or `const' opcode used, in bits.  Zero means the
117       expression has no such instructions.  */
118    int max_data_size;
119
120    /* Bit vector of registers needed.  Register R is needed iff
121
122       reg_mask[R / 8] & (1 << (R % 8))
123
124       is non-zero.  Note!  You may not assume that this bitmask is long
125       enough to hold bits for all the registers of the machine; the
126       agent expression code has no idea how many registers the machine
127       has.  However, the bitmask is reg_mask_len bytes long, so the
128       valid register numbers run from 0 to reg_mask_len * 8 - 1.
129
130       Also note that this mask may contain registers that are needed
131       for the original collection expression to work, but that are
132       not referenced by any bytecode.  This could, for example, occur
133       when collecting a local variable allocated to a register; the
134       compiler sets the mask bit and skips generating a bytecode whose
135       result is going to be discarded anyway.
136    */
137    int reg_mask_len;
138    unsigned char *reg_mask;
139
140    /* For the data tracing facility, we need to insert `trace' bytecodes
141       before each data fetch; this records all the memory that the
142       expression touches in the course of evaluation, so that memory will
143       be available when the user later tries to evaluate the expression
144       in GDB.
145
146       Setting the flag 'tracing' to non-zero enables the code that
147       emits the trace bytecodes at the appropriate points.  */
148
149    unsigned int tracing : 1;
150
151    /* This indicates that pointers to chars should get an added
152       tracenz bytecode to record nonzero bytes, up to a length that
153       is the value of trace_string.  */
154
155    int trace_string;
156  };
157
158/* An agent_expr owning pointer.  */
159typedef std::unique_ptr<agent_expr> agent_expr_up;
160
161/* The actual values of the various bytecode operations.  */
162
163enum agent_op
164  {
165#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE)  \
166    aop_ ## NAME = VALUE,
167#include "common/ax.def"
168#undef DEFOP
169    aop_last
170  };
171
172
173
174/* Functions for building expressions.  */
175
176/* Append a raw byte to EXPR.  */
177extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
178
179/* Append a simple operator OP to EXPR.  */
180extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
181
182/* Append a pick operator to EXPR.  DEPTH is the stack item to pick,
183   with 0 being top of stack.  */
184extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
185
186/* Append the floating-point prefix, for the next bytecode.  */
187#define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
188
189/* Append a sign-extension instruction to EXPR, to extend an N-bit value.  */
190extern void ax_ext (struct agent_expr *EXPR, int N);
191
192/* Append a zero-extension instruction to EXPR, to extend an N-bit value.  */
193extern void ax_zero_ext (struct agent_expr *EXPR, int N);
194
195/* Append a trace_quick instruction to EXPR, to record N bytes.  */
196extern void ax_trace_quick (struct agent_expr *EXPR, int N);
197
198/* Append a goto op to EXPR.  OP is the actual op (must be aop_goto or
199   aop_if_goto).  We assume we don't know the target offset yet,
200   because it's probably a forward branch, so we leave space in EXPR
201   for the target, and return the offset in EXPR of that space, so we
202   can backpatch it once we do know the target offset.  Use ax_label
203   to do the backpatching.  */
204extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
205
206/* Suppose a given call to ax_goto returns some value PATCH.  When you
207   know the offset TARGET that goto should jump to, call
208   ax_label (EXPR, PATCH, TARGET)
209   to patch TARGET into the ax_goto instruction.  */
210extern void ax_label (struct agent_expr *EXPR, int patch, int target);
211
212/* Assemble code to push a constant on the stack.  */
213extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
214extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
215
216/* Assemble code to push the value of register number REG on the
217   stack.  */
218extern void ax_reg (struct agent_expr *EXPR, int REG);
219
220/* Add the given register to the register mask of the expression.  */
221extern void ax_reg_mask (struct agent_expr *ax, int reg);
222
223/* Assemble code to operate on a trace state variable.  */
224extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
225
226/* Append a string to the bytecode stream.  */
227extern void ax_string (struct agent_expr *x, const char *str, int slen);
228
229
230/* Functions for printing out expressions, and otherwise debugging
231   things.  */
232
233/* Disassemble the expression EXPR, writing to F.  */
234extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
235
236/* An entry in the opcode map.  */
237struct aop_map
238  {
239
240    /* The name of the opcode.  Null means that this entry is not a
241       valid opcode --- a hole in the opcode space.  */
242    const char *name;
243
244    /* All opcodes take no operands from the bytecode stream, or take
245       unsigned integers of various sizes.  If this is a positive number
246       n, then the opcode is followed by an n-byte operand, which should
247       be printed as an unsigned integer.  If this is zero, then the
248       opcode takes no operands from the bytecode stream.
249
250       If we get more complicated opcodes in the future, don't add other
251       magic values of this; that's a crock.  Add an `enum encoding'
252       field to this, or something like that.  */
253    int op_size;
254
255    /* The size of the data operated upon, in bits, for bytecodes that
256       care about that (ref and const).  Zero for all others.  */
257    int data_size;
258
259    /* Number of stack elements consumed, and number produced.  */
260    int consumed, produced;
261  };
262
263/* Map of the bytecodes, indexed by bytecode number.  */
264extern struct aop_map aop_map[];
265
266/* Given an agent expression AX, analyze and update its requirements.  */
267
268extern void ax_reqs (struct agent_expr *ax);
269
270#endif /* AX_H */
271