1 /* Definitions for expressions designed to be executed on the agent 2 Copyright (C) 1998-2024 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. */ 53 enum 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. */ 81 struct agent_expr 82 { 83 /* Construct an empty agent expression. */ agent_expragent_expr84 agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope) 85 : gdbarch (gdbarch), 86 scope (scope) 87 { } 88 89 /* The bytes of the expression. */ 90 gdb::byte_vector buf; 91 92 /* The target architecture assumed to be in effect. */ 93 struct gdbarch *gdbarch; 94 95 /* The address to which the expression applies. */ 96 CORE_ADDR scope; 97 98 /* If the following is not equal to agent_flaw_none, the rest of the 99 information in this structure is suspect. */ 100 enum agent_flaws flaw; 101 102 /* Number of elements left on stack at end; may be negative if expr 103 only consumes elements. */ 104 int final_height; 105 106 /* Maximum and minimum stack height, relative to initial height. */ 107 int max_height, min_height; 108 109 /* Largest `ref' or `const' opcode used, in bits. Zero means the 110 expression has no such instructions. */ 111 int max_data_size; 112 113 /* Bit vector of registers needed. Register R is needed iff 114 reg_mask[R] is non-zero. Note! You may not assume that this 115 bitmask is long enough to hold bits for all the registers of 116 the machine; the agent expression code has no idea how many 117 registers the machine has. 118 119 Also note that this mask may contain registers that are needed 120 for the original collection expression to work, but that are 121 not referenced by any bytecode. This could, for example, occur 122 when collecting a local variable allocated to a register; the 123 compiler sets the mask bit and skips generating a bytecode whose 124 result is going to be discarded anyway. 125 */ 126 std::vector<bool> reg_mask; 127 128 /* For the data tracing facility, we need to insert `trace' bytecodes 129 before each data fetch; this records all the memory that the 130 expression touches in the course of evaluation, so that memory will 131 be available when the user later tries to evaluate the expression 132 in GDB. 133 134 Setting the flag 'tracing' to true enables the code that 135 emits the trace bytecodes at the appropriate points. */ 136 137 bool tracing = false; 138 139 /* This indicates that pointers to chars should get an added 140 tracenz bytecode to record nonzero bytes, up to a length that 141 is the value of trace_string. */ 142 143 int trace_string = 0; 144 }; 145 146 /* An agent_expr owning pointer. */ 147 typedef std::unique_ptr<agent_expr> agent_expr_up; 148 149 /* The actual values of the various bytecode operations. */ 150 151 enum agent_op 152 { 153 #define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE) \ 154 aop_ ## NAME = VALUE, 155 #include "gdbsupport/ax.def" 156 #undef DEFOP 157 }; 158 159 160 161 /* Functions for building expressions. */ 162 163 /* Append a raw byte to EXPR. */ 164 extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte); 165 166 /* Append a simple operator OP to EXPR. */ 167 extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP); 168 169 /* Append a pick operator to EXPR. DEPTH is the stack item to pick, 170 with 0 being top of stack. */ 171 extern void ax_pick (struct agent_expr *EXPR, int DEPTH); 172 173 /* Append the floating-point prefix, for the next bytecode. */ 174 #define ax_float(EXPR) (ax_simple ((EXPR), aop_float)) 175 176 /* Append a sign-extension instruction to EXPR, to extend an N-bit value. */ 177 extern void ax_ext (struct agent_expr *EXPR, int N); 178 179 /* Append a zero-extension instruction to EXPR, to extend an N-bit value. */ 180 extern void ax_zero_ext (struct agent_expr *EXPR, int N); 181 182 /* Append a trace_quick instruction to EXPR, to record N bytes. */ 183 extern void ax_trace_quick (struct agent_expr *EXPR, int N); 184 185 /* Append a goto op to EXPR. OP is the actual op (must be aop_goto or 186 aop_if_goto). We assume we don't know the target offset yet, 187 because it's probably a forward branch, so we leave space in EXPR 188 for the target, and return the offset in EXPR of that space, so we 189 can backpatch it once we do know the target offset. Use ax_label 190 to do the backpatching. */ 191 extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP); 192 193 /* Suppose a given call to ax_goto returns some value PATCH. When you 194 know the offset TARGET that goto should jump to, call 195 ax_label (EXPR, PATCH, TARGET) 196 to patch TARGET into the ax_goto instruction. */ 197 extern void ax_label (struct agent_expr *EXPR, int patch, int target); 198 199 /* Assemble code to push a constant on the stack. */ 200 extern void ax_const_l (struct agent_expr *EXPR, LONGEST l); 201 extern void ax_const_d (struct agent_expr *EXPR, LONGEST d); 202 203 /* Assemble code to push the value of register number REG on the 204 stack. */ 205 extern void ax_reg (struct agent_expr *EXPR, int REG); 206 207 /* Add the given register to the register mask of the expression. */ 208 extern void ax_reg_mask (struct agent_expr *ax, int reg); 209 210 /* Assemble code to operate on a trace state variable. */ 211 extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num); 212 213 /* Append a string to the bytecode stream. */ 214 extern void ax_string (struct agent_expr *x, const char *str, int slen); 215 216 217 /* Functions for printing out expressions, and otherwise debugging 218 things. */ 219 220 /* Disassemble the expression EXPR, writing to F. */ 221 extern void ax_print (struct ui_file *f, struct agent_expr * EXPR); 222 223 /* Given an agent expression AX, analyze and update its requirements. */ 224 225 extern void ax_reqs (struct agent_expr *ax); 226 227 #endif /* AX_H */ 228