301 lines
12 KiB
C
301 lines
12 KiB
C
/* Interface to prologue value handling for GDB.
|
|
Copyright 2003, 2004, 2005, 2007, 2008, 2009 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 PROLOGUE_VALUE_H
|
|
#define PROLOGUE_VALUE_H
|
|
|
|
/* When we analyze a prologue, we're really doing 'abstract
|
|
interpretation' or 'pseudo-evaluation': running the function's code
|
|
in simulation, but using conservative approximations of the values
|
|
it would have when it actually runs. For example, if our function
|
|
starts with the instruction:
|
|
|
|
addi r1, 42 # add 42 to r1
|
|
|
|
we don't know exactly what value will be in r1 after executing this
|
|
instruction, but we do know it'll be 42 greater than its original
|
|
value.
|
|
|
|
If we then see an instruction like:
|
|
|
|
addi r1, 22 # add 22 to r1
|
|
|
|
we still don't know what r1's value is, but again, we can say it is
|
|
now 64 greater than its original value.
|
|
|
|
If the next instruction were:
|
|
|
|
mov r2, r1 # set r2 to r1's value
|
|
|
|
then we can say that r2's value is now the original value of r1
|
|
plus 64.
|
|
|
|
It's common for prologues to save registers on the stack, so we'll
|
|
need to track the values of stack frame slots, as well as the
|
|
registers. So after an instruction like this:
|
|
|
|
mov (fp+4), r2
|
|
|
|
then we'd know that the stack slot four bytes above the frame
|
|
pointer holds the original value of r1 plus 64.
|
|
|
|
And so on.
|
|
|
|
Of course, this can only go so far before it gets unreasonable. If
|
|
we wanted to be able to say anything about the value of r1 after
|
|
the instruction:
|
|
|
|
xor r1, r3 # exclusive-or r1 and r3, place result in r1
|
|
|
|
then things would get pretty complex. But remember, we're just
|
|
doing a conservative approximation; if exclusive-or instructions
|
|
aren't relevant to prologues, we can just say r1's value is now
|
|
'unknown'. We can ignore things that are too complex, if that loss
|
|
of information is acceptable for our application.
|
|
|
|
So when I say "conservative approximation" here, what I mean is an
|
|
approximation that is either accurate, or marked "unknown", but
|
|
never inaccurate.
|
|
|
|
Once you've reached the current PC, or an instruction that you
|
|
don't know how to simulate, you stop. Now you can examine the
|
|
state of the registers and stack slots you've kept track of.
|
|
|
|
- To see how large your stack frame is, just check the value of the
|
|
stack pointer register; if it's the original value of the SP
|
|
minus a constant, then that constant is the stack frame's size.
|
|
If the SP's value has been marked as 'unknown', then that means
|
|
the prologue has done something too complex for us to track, and
|
|
we don't know the frame size.
|
|
|
|
- To see where we've saved the previous frame's registers, we just
|
|
search the values we've tracked --- stack slots, usually, but
|
|
registers, too, if you want --- for something equal to the
|
|
register's original value. If the ABI suggests a standard place
|
|
to save a given register, then we can check there first, but
|
|
really, anything that will get us back the original value will
|
|
probably work.
|
|
|
|
Sure, this takes some work. But prologue analyzers aren't
|
|
quick-and-simple pattern patching to recognize a few fixed prologue
|
|
forms any more; they're big, hairy functions. Along with inferior
|
|
function calls, prologue analysis accounts for a substantial
|
|
portion of the time needed to stabilize a GDB port. So I think
|
|
it's worthwhile to look for an approach that will be easier to
|
|
understand and maintain. In the approach used here:
|
|
|
|
- It's easier to see that the analyzer is correct: you just see
|
|
whether the analyzer properly (albiet conservatively) simulates
|
|
the effect of each instruction.
|
|
|
|
- It's easier to extend the analyzer: you can add support for new
|
|
instructions, and know that you haven't broken anything that
|
|
wasn't already broken before.
|
|
|
|
- It's orthogonal: to gather new information, you don't need to
|
|
complicate the code for each instruction. As long as your domain
|
|
of conservative values is already detailed enough to tell you
|
|
what you need, then all the existing instruction simulations are
|
|
already gathering the right data for you.
|
|
|
|
A 'struct prologue_value' is a conservative approximation of the
|
|
real value the register or stack slot will have. */
|
|
|
|
struct prologue_value {
|
|
|
|
/* What sort of value is this? This determines the interpretation
|
|
of subsequent fields. */
|
|
enum {
|
|
|
|
/* We don't know anything about the value. This is also used for
|
|
values we could have kept track of, when doing so would have
|
|
been too complex and we don't want to bother. The bottom of
|
|
our lattice. */
|
|
pvk_unknown,
|
|
|
|
/* A known constant. K is its value. */
|
|
pvk_constant,
|
|
|
|
/* The value that register REG originally had *UPON ENTRY TO THE
|
|
FUNCTION*, plus K. If K is zero, this means, obviously, just
|
|
the value REG had upon entry to the function. REG is a GDB
|
|
register number. Before we start interpreting, we initialize
|
|
every register R to { pvk_register, R, 0 }. */
|
|
pvk_register,
|
|
|
|
} kind;
|
|
|
|
/* The meanings of the following fields depend on 'kind'; see the
|
|
comments for the specific 'kind' values. */
|
|
int reg;
|
|
CORE_ADDR k;
|
|
};
|
|
|
|
typedef struct prologue_value pv_t;
|
|
|
|
|
|
/* Return the unknown prologue value --- { pvk_unknown, ?, ? }. */
|
|
pv_t pv_unknown (void);
|
|
|
|
/* Return the prologue value representing the constant K. */
|
|
pv_t pv_constant (CORE_ADDR k);
|
|
|
|
/* Return the prologue value representing the original value of
|
|
register REG, plus the constant K. */
|
|
pv_t pv_register (int reg, CORE_ADDR k);
|
|
|
|
|
|
/* Return conservative approximations of the results of the following
|
|
operations. */
|
|
pv_t pv_add (pv_t a, pv_t b); /* a + b */
|
|
pv_t pv_add_constant (pv_t v, CORE_ADDR k); /* a + k */
|
|
pv_t pv_subtract (pv_t a, pv_t b); /* a - b */
|
|
pv_t pv_logical_and (pv_t a, pv_t b); /* a & b */
|
|
|
|
|
|
/* Return non-zero iff A and B are identical expressions.
|
|
|
|
This is not the same as asking if the two values are equal; the
|
|
result of such a comparison would have to be a pv_boolean, and
|
|
asking whether two 'unknown' values were equal would give you
|
|
pv_maybe. Same for comparing, say, { pvk_register, R1, 0 } and {
|
|
pvk_register, R2, 0}.
|
|
|
|
Instead, this function asks whether the two representations are the
|
|
same. */
|
|
int pv_is_identical (pv_t a, pv_t b);
|
|
|
|
|
|
/* Return non-zero if A is known to be a constant. */
|
|
int pv_is_constant (pv_t a);
|
|
|
|
/* Return non-zero if A is the original value of register number R
|
|
plus some constant, zero otherwise. */
|
|
int pv_is_register (pv_t a, int r);
|
|
|
|
|
|
/* Return non-zero if A is the original value of register R plus the
|
|
constant K. */
|
|
int pv_is_register_k (pv_t a, int r, CORE_ADDR k);
|
|
|
|
/* A conservative boolean type, including "maybe", when we can't
|
|
figure out whether something is true or not. */
|
|
enum pv_boolean {
|
|
pv_maybe,
|
|
pv_definite_yes,
|
|
pv_definite_no,
|
|
};
|
|
|
|
|
|
/* Decide whether a reference to SIZE bytes at ADDR refers exactly to
|
|
an element of an array. The array starts at ARRAY_ADDR, and has
|
|
ARRAY_LEN values of ELT_SIZE bytes each. If ADDR definitely does
|
|
refer to an array element, set *I to the index of the referenced
|
|
element in the array, and return pv_definite_yes. If it definitely
|
|
doesn't, return pv_definite_no. If we can't tell, return pv_maybe.
|
|
|
|
If the reference does touch the array, but doesn't fall exactly on
|
|
an element boundary, or doesn't refer to the whole element, return
|
|
pv_maybe. */
|
|
enum pv_boolean pv_is_array_ref (pv_t addr, CORE_ADDR size,
|
|
pv_t array_addr, CORE_ADDR array_len,
|
|
CORE_ADDR elt_size,
|
|
int *i);
|
|
|
|
|
|
/* A 'struct pv_area' keeps track of values stored in a particular
|
|
region of memory. */
|
|
struct pv_area;
|
|
|
|
/* Create a new area, tracking stores relative to the original value
|
|
of BASE_REG. If BASE_REG is SP, then this effectively records the
|
|
contents of the stack frame: the original value of the SP is the
|
|
frame's CFA, or some constant offset from it.
|
|
|
|
Stores to constant addresses, unknown addresses, or to addresses
|
|
relative to registers other than BASE_REG will trash this area; see
|
|
pv_area_store_would_trash.
|
|
|
|
To check whether a pointer refers to this area, only the low
|
|
ADDR_BIT bits will be compared. */
|
|
struct pv_area *make_pv_area (int base_reg, int addr_bit);
|
|
|
|
/* Free AREA. */
|
|
void free_pv_area (struct pv_area *area);
|
|
|
|
|
|
/* Register a cleanup to free AREA. */
|
|
struct cleanup *make_cleanup_free_pv_area (struct pv_area *area);
|
|
|
|
|
|
/* Store the SIZE-byte value VALUE at ADDR in AREA.
|
|
|
|
If ADDR is not relative to the same base register we used in
|
|
creating AREA, then we can't tell which values here the stored
|
|
value might overlap, and we'll have to mark everything as
|
|
unknown. */
|
|
void pv_area_store (struct pv_area *area,
|
|
pv_t addr,
|
|
CORE_ADDR size,
|
|
pv_t value);
|
|
|
|
/* Return the SIZE-byte value at ADDR in AREA. This may return
|
|
pv_unknown (). */
|
|
pv_t pv_area_fetch (struct pv_area *area, pv_t addr, CORE_ADDR size);
|
|
|
|
/* Return true if storing to address ADDR in AREA would force us to
|
|
mark the contents of the entire area as unknown. This could happen
|
|
if, say, ADDR is unknown, since we could be storing anywhere. Or,
|
|
it could happen if ADDR is relative to a different register than
|
|
the other stores base register, since we don't know the relative
|
|
values of the two registers.
|
|
|
|
If you've reached such a store, it may be better to simply stop the
|
|
prologue analysis, and return the information you've gathered,
|
|
instead of losing all that information, most of which is probably
|
|
okay. */
|
|
int pv_area_store_would_trash (struct pv_area *area, pv_t addr);
|
|
|
|
|
|
/* Search AREA for the original value of REGISTER. If we can't find
|
|
it, return zero; if we can find it, return a non-zero value, and if
|
|
OFFSET_P is non-zero, set *OFFSET_P to the register's offset within
|
|
AREA. GDBARCH is the architecture of which REGISTER is a member.
|
|
|
|
In the worst case, this takes time proportional to the number of
|
|
items stored in AREA. If you plan to gather a lot of information
|
|
about registers saved in AREA, consider calling pv_area_scan
|
|
instead, and collecting all your information in one pass. */
|
|
int pv_area_find_reg (struct pv_area *area,
|
|
struct gdbarch *gdbarch,
|
|
int reg,
|
|
CORE_ADDR *offset_p);
|
|
|
|
|
|
/* For every part of AREA whose value we know, apply FUNC to CLOSURE,
|
|
the value's address, its size, and the value itself. */
|
|
void pv_area_scan (struct pv_area *area,
|
|
void (*func) (void *closure,
|
|
pv_t addr,
|
|
CORE_ADDR size,
|
|
pv_t value),
|
|
void *closure);
|
|
|
|
|
|
#endif /* PROLOGUE_VALUE_H */
|