ax.h revision 1.9
1/* Definitions for expressions designed to be executed on the agent 2 Copyright (C) 1998-2020 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/* It's sometimes useful to be able to debug programs that you can't 23 really stop for more than a fraction of a second. To this end, the 24 user can specify a tracepoint (like a breakpoint, but you don't 25 stop at it), and specify a bunch of expressions to record the 26 values of when that tracepoint is reached. As the program runs, 27 GDB collects the values. At any point (possibly while values are 28 still being collected), the user can display the collected values. 29 30 This is used with remote debugging; we don't really support it on 31 native configurations. 32 33 This means that expressions are being evaluated by the remote agent, 34 which doesn't have any access to the symbol table information, and 35 needs to be small and simple. 36 37 The agent_expr routines and datatypes are a bytecode language 38 designed to be executed by the agent. Agent expressions work in 39 terms of fixed-width values, operators, memory references, and 40 register references. You can evaluate a agent expression just given 41 a bunch of memory and register values to sniff at; you don't need 42 any symbolic information like variable names, types, etc. 43 44 GDB translates source expressions, whose meaning depends on 45 symbolic information, into agent bytecode expressions, whose meaning 46 is independent of symbolic information. This means the agent can 47 evaluate them on the fly without reference to data only available 48 to the host GDB. */ 49 50 51/* Different kinds of flaws an agent expression might have, as 52 detected by ax_reqs. */ 53enum agent_flaws 54 { 55 agent_flaw_none = 0, /* code is good */ 56 57 /* There is an invalid instruction in the stream. */ 58 agent_flaw_bad_instruction, 59 60 /* There is an incomplete instruction at the end of the expression. */ 61 agent_flaw_incomplete_instruction, 62 63 /* ax_reqs was unable to prove that every jump target is to a 64 valid offset. Valid offsets are within the bounds of the 65 expression, and to a valid instruction boundary. */ 66 agent_flaw_bad_jump, 67 68 /* ax_reqs was unable to prove to its satisfaction that, for each 69 jump target location, the stack will have the same height whether 70 that location is reached via a jump or by straight execution. */ 71 agent_flaw_height_mismatch, 72 73 /* ax_reqs was unable to prove that every instruction following 74 an unconditional jump was the target of some other jump. */ 75 agent_flaw_hole 76 }; 77 78/* Agent expression data structures. */ 79 80/* A buffer containing a agent expression. */ 81struct agent_expr 82 { 83 /* Construct an empty agent expression. */ 84 explicit agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope); 85 86 ~agent_expr (); 87 88 /* The bytes of the expression. */ 89 unsigned char *buf; 90 91 /* The number of bytecode in the expression. */ 92 int len; 93 94 /* Allocated space available currently. */ 95 int size; 96 97 /* The target architecture assumed to be in effect. */ 98 struct gdbarch *gdbarch; 99 100 /* The address to which the expression applies. */ 101 CORE_ADDR scope; 102 103 /* If the following is not equal to agent_flaw_none, the rest of the 104 information in this structure is suspect. */ 105 enum agent_flaws flaw; 106 107 /* Number of elements left on stack at end; may be negative if expr 108 only consumes elements. */ 109 int final_height; 110 111 /* Maximum and minimum stack height, relative to initial height. */ 112 int max_height, min_height; 113 114 /* Largest `ref' or `const' opcode used, in bits. Zero means the 115 expression has no such instructions. */ 116 int max_data_size; 117 118 /* Bit vector of registers needed. Register R is needed iff 119 120 reg_mask[R / 8] & (1 << (R % 8)) 121 122 is non-zero. Note! You may not assume that this bitmask is long 123 enough to hold bits for all the registers of the machine; the 124 agent expression code has no idea how many registers the machine 125 has. However, the bitmask is reg_mask_len bytes long, so the 126 valid register numbers run from 0 to reg_mask_len * 8 - 1. 127 128 Also note that this mask may contain registers that are needed 129 for the original collection expression to work, but that are 130 not referenced by any bytecode. This could, for example, occur 131 when collecting a local variable allocated to a register; the 132 compiler sets the mask bit and skips generating a bytecode whose 133 result is going to be discarded anyway. 134 */ 135 int reg_mask_len; 136 unsigned char *reg_mask; 137 138 /* For the data tracing facility, we need to insert `trace' bytecodes 139 before each data fetch; this records all the memory that the 140 expression touches in the course of evaluation, so that memory will 141 be available when the user later tries to evaluate the expression 142 in GDB. 143 144 Setting the flag 'tracing' to non-zero enables the code that 145 emits the trace bytecodes at the appropriate points. */ 146 147 unsigned int tracing : 1; 148 149 /* This indicates that pointers to chars should get an added 150 tracenz bytecode to record nonzero bytes, up to a length that 151 is the value of trace_string. */ 152 153 int trace_string; 154 }; 155 156/* An agent_expr owning pointer. */ 157typedef std::unique_ptr<agent_expr> agent_expr_up; 158 159/* The actual values of the various bytecode operations. */ 160 161enum agent_op 162 { 163#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE) \ 164 aop_ ## NAME = VALUE, 165#include "gdbsupport/ax.def" 166#undef DEFOP 167 aop_last 168 }; 169 170 171 172/* Functions for building expressions. */ 173 174/* Append a raw byte to EXPR. */ 175extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte); 176 177/* Append a simple operator OP to EXPR. */ 178extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP); 179 180/* Append a pick operator to EXPR. DEPTH is the stack item to pick, 181 with 0 being top of stack. */ 182extern void ax_pick (struct agent_expr *EXPR, int DEPTH); 183 184/* Append the floating-point prefix, for the next bytecode. */ 185#define ax_float(EXPR) (ax_simple ((EXPR), aop_float)) 186 187/* Append a sign-extension instruction to EXPR, to extend an N-bit value. */ 188extern void ax_ext (struct agent_expr *EXPR, int N); 189 190/* Append a zero-extension instruction to EXPR, to extend an N-bit value. */ 191extern void ax_zero_ext (struct agent_expr *EXPR, int N); 192 193/* Append a trace_quick instruction to EXPR, to record N bytes. */ 194extern void ax_trace_quick (struct agent_expr *EXPR, int N); 195 196/* Append a goto op to EXPR. OP is the actual op (must be aop_goto or 197 aop_if_goto). We assume we don't know the target offset yet, 198 because it's probably a forward branch, so we leave space in EXPR 199 for the target, and return the offset in EXPR of that space, so we 200 can backpatch it once we do know the target offset. Use ax_label 201 to do the backpatching. */ 202extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP); 203 204/* Suppose a given call to ax_goto returns some value PATCH. When you 205 know the offset TARGET that goto should jump to, call 206 ax_label (EXPR, PATCH, TARGET) 207 to patch TARGET into the ax_goto instruction. */ 208extern void ax_label (struct agent_expr *EXPR, int patch, int target); 209 210/* Assemble code to push a constant on the stack. */ 211extern void ax_const_l (struct agent_expr *EXPR, LONGEST l); 212extern void ax_const_d (struct agent_expr *EXPR, LONGEST d); 213 214/* Assemble code to push the value of register number REG on the 215 stack. */ 216extern void ax_reg (struct agent_expr *EXPR, int REG); 217 218/* Add the given register to the register mask of the expression. */ 219extern void ax_reg_mask (struct agent_expr *ax, int reg); 220 221/* Assemble code to operate on a trace state variable. */ 222extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num); 223 224/* Append a string to the bytecode stream. */ 225extern void ax_string (struct agent_expr *x, const char *str, int slen); 226 227 228/* Functions for printing out expressions, and otherwise debugging 229 things. */ 230 231/* Disassemble the expression EXPR, writing to F. */ 232extern void ax_print (struct ui_file *f, struct agent_expr * EXPR); 233 234/* An entry in the opcode map. */ 235struct aop_map 236 { 237 238 /* The name of the opcode. Null means that this entry is not a 239 valid opcode --- a hole in the opcode space. */ 240 const char *name; 241 242 /* All opcodes take no operands from the bytecode stream, or take 243 unsigned integers of various sizes. If this is a positive number 244 n, then the opcode is followed by an n-byte operand, which should 245 be printed as an unsigned integer. If this is zero, then the 246 opcode takes no operands from the bytecode stream. 247 248 If we get more complicated opcodes in the future, don't add other 249 magic values of this; that's a crock. Add an `enum encoding' 250 field to this, or something like that. */ 251 int op_size; 252 253 /* The size of the data operated upon, in bits, for bytecodes that 254 care about that (ref and const). Zero for all others. */ 255 int data_size; 256 257 /* Number of stack elements consumed, and number produced. */ 258 int consumed, produced; 259 }; 260 261/* Map of the bytecodes, indexed by bytecode number. */ 262extern struct aop_map aop_map[]; 263 264/* Given an agent expression AX, analyze and update its requirements. */ 265 266extern void ax_reqs (struct agent_expr *ax); 267 268#endif /* AX_H */ 269