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/* Definitions for expressions designed to be executed on the agent
Copyright (C) 1998-2023 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef AX_H
#define AX_H
/* It's sometimes useful to be able to debug programs that you can't
really stop for more than a fraction of a second. To this end, the
user can specify a tracepoint (like a breakpoint, but you don't
stop at it), and specify a bunch of expressions to record the
values of when that tracepoint is reached. As the program runs,
GDB collects the values. At any point (possibly while values are
still being collected), the user can display the collected values.
This is used with remote debugging; we don't really support it on
native configurations.
This means that expressions are being evaluated by the remote agent,
which doesn't have any access to the symbol table information, and
needs to be small and simple.
The agent_expr routines and datatypes are a bytecode language
designed to be executed by the agent. Agent expressions work in
terms of fixed-width values, operators, memory references, and
register references. You can evaluate a agent expression just given
a bunch of memory and register values to sniff at; you don't need
any symbolic information like variable names, types, etc.
GDB translates source expressions, whose meaning depends on
symbolic information, into agent bytecode expressions, whose meaning
is independent of symbolic information. This means the agent can
evaluate them on the fly without reference to data only available
to the host GDB. */
/* Different kinds of flaws an agent expression might have, as
detected by ax_reqs. */
enum agent_flaws
{
agent_flaw_none = 0, /* code is good */
/* There is an invalid instruction in the stream. */
agent_flaw_bad_instruction,
/* There is an incomplete instruction at the end of the expression. */
agent_flaw_incomplete_instruction,
/* ax_reqs was unable to prove that every jump target is to a
valid offset. Valid offsets are within the bounds of the
expression, and to a valid instruction boundary. */
agent_flaw_bad_jump,
/* ax_reqs was unable to prove to its satisfaction that, for each
jump target location, the stack will have the same height whether
that location is reached via a jump or by straight execution. */
agent_flaw_height_mismatch,
/* ax_reqs was unable to prove that every instruction following
an unconditional jump was the target of some other jump. */
agent_flaw_hole
};
/* Agent expression data structures. */
/* A buffer containing a agent expression. */
struct agent_expr
{
/* Construct an empty agent expression. */
agent_expr (struct gdbarch *gdbarch, CORE_ADDR scope)
: gdbarch (gdbarch),
scope (scope)
{ }
/* The bytes of the expression. */
gdb::byte_vector buf;
/* The target architecture assumed to be in effect. */
struct gdbarch *gdbarch;
/* The address to which the expression applies. */
CORE_ADDR scope;
/* If the following is not equal to agent_flaw_none, the rest of the
information in this structure is suspect. */
enum agent_flaws flaw;
/* Number of elements left on stack at end; may be negative if expr
only consumes elements. */
int final_height;
/* Maximum and minimum stack height, relative to initial height. */
int max_height, min_height;
/* Largest `ref' or `const' opcode used, in bits. Zero means the
expression has no such instructions. */
int max_data_size;
/* Bit vector of registers needed. Register R is needed iff
reg_mask[R] is non-zero. Note! You may not assume that this
bitmask is long enough to hold bits for all the registers of
the machine; the agent expression code has no idea how many
registers the machine has.
Also note that this mask may contain registers that are needed
for the original collection expression to work, but that are
not referenced by any bytecode. This could, for example, occur
when collecting a local variable allocated to a register; the
compiler sets the mask bit and skips generating a bytecode whose
result is going to be discarded anyway.
*/
std::vector<bool> reg_mask;
/* For the data tracing facility, we need to insert `trace' bytecodes
before each data fetch; this records all the memory that the
expression touches in the course of evaluation, so that memory will
be available when the user later tries to evaluate the expression
in GDB.
Setting the flag 'tracing' to true enables the code that
emits the trace bytecodes at the appropriate points. */
bool tracing = false;
/* This indicates that pointers to chars should get an added
tracenz bytecode to record nonzero bytes, up to a length that
is the value of trace_string. */
int trace_string = 0;
};
/* An agent_expr owning pointer. */
typedef std::unique_ptr<agent_expr> agent_expr_up;
/* The actual values of the various bytecode operations. */
enum agent_op
{
#define DEFOP(NAME, SIZE, DATA_SIZE, CONSUMED, PRODUCED, VALUE) \
aop_ ## NAME = VALUE,
#include "gdbsupport/ax.def"
#undef DEFOP
};
/* Functions for building expressions. */
/* Append a raw byte to EXPR. */
extern void ax_raw_byte (struct agent_expr *expr, gdb_byte byte);
/* Append a simple operator OP to EXPR. */
extern void ax_simple (struct agent_expr *EXPR, enum agent_op OP);
/* Append a pick operator to EXPR. DEPTH is the stack item to pick,
with 0 being top of stack. */
extern void ax_pick (struct agent_expr *EXPR, int DEPTH);
/* Append the floating-point prefix, for the next bytecode. */
#define ax_float(EXPR) (ax_simple ((EXPR), aop_float))
/* Append a sign-extension instruction to EXPR, to extend an N-bit value. */
extern void ax_ext (struct agent_expr *EXPR, int N);
/* Append a zero-extension instruction to EXPR, to extend an N-bit value. */
extern void ax_zero_ext (struct agent_expr *EXPR, int N);
/* Append a trace_quick instruction to EXPR, to record N bytes. */
extern void ax_trace_quick (struct agent_expr *EXPR, int N);
/* Append a goto op to EXPR. OP is the actual op (must be aop_goto or
aop_if_goto). We assume we don't know the target offset yet,
because it's probably a forward branch, so we leave space in EXPR
for the target, and return the offset in EXPR of that space, so we
can backpatch it once we do know the target offset. Use ax_label
to do the backpatching. */
extern int ax_goto (struct agent_expr *EXPR, enum agent_op OP);
/* Suppose a given call to ax_goto returns some value PATCH. When you
know the offset TARGET that goto should jump to, call
ax_label (EXPR, PATCH, TARGET)
to patch TARGET into the ax_goto instruction. */
extern void ax_label (struct agent_expr *EXPR, int patch, int target);
/* Assemble code to push a constant on the stack. */
extern void ax_const_l (struct agent_expr *EXPR, LONGEST l);
extern void ax_const_d (struct agent_expr *EXPR, LONGEST d);
/* Assemble code to push the value of register number REG on the
stack. */
extern void ax_reg (struct agent_expr *EXPR, int REG);
/* Add the given register to the register mask of the expression. */
extern void ax_reg_mask (struct agent_expr *ax, int reg);
/* Assemble code to operate on a trace state variable. */
extern void ax_tsv (struct agent_expr *expr, enum agent_op op, int num);
/* Append a string to the bytecode stream. */
extern void ax_string (struct agent_expr *x, const char *str, int slen);
/* Functions for printing out expressions, and otherwise debugging
things. */
/* Disassemble the expression EXPR, writing to F. */
extern void ax_print (struct ui_file *f, struct agent_expr * EXPR);
/* Given an agent expression AX, analyze and update its requirements. */
extern void ax_reqs (struct agent_expr *ax);
#endif /* AX_H */
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