From 7d30c22d4c26dfe28d06602bee825be609a36858 Mon Sep 17 00:00:00 2001 From: Jim Blandy Date: Tue, 28 Mar 2006 19:19:16 +0000 Subject: src/gdb/ChangeLog: 2006-03-28 Jim Blandy * prologue-value.c, prologue-value.h: New files. * Makefile.in (prologue_value_h): New variable. (HFILES_NO_SRCDIR): List prologue-value.h. (SFILES): List prologue-value.c. (COMMON_OBS): List prologue-value.o. (prologue-value.o): New rule. src/gdb/doc/ChangeLog: 2006-03-28 Jim Blandy * gdbint.texinfo (Prologue Analysis): New section. --- gdb/prologue-value.h | 302 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 302 insertions(+) create mode 100644 gdb/prologue-value.h (limited to 'gdb/prologue-value.h') diff --git a/gdb/prologue-value.h b/gdb/prologue-value.h new file mode 100644 index 0000000..ec44cad --- /dev/null +++ b/gdb/prologue-value.h @@ -0,0 +1,302 @@ +/* Interface to prologue value handling for GDB. + Copyright 2003, 2004, 2005 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 2 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, write to: + + Free Software Foundation, Inc. + 51 Franklin St - Fifth Floor + Boston, MA 02110-1301 + USA */ + +#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. */ +struct pv_area *make_pv_area (int base_reg); + +/* 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 register, + 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 */ -- cgit v1.1