// verify.cc - verify bytecode
-/* Copyright (C) 2001, 2002, 2003 Free Software Foundation
+/* Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation
This file is part of libgcj.
#include <java-insns.h>
#include <java-interp.h>
+// On Solaris 10/x86, <signal.h> indirectly includes <ia32/sys/reg.h>, which
+// defines PC since g++ predefines __EXTENSIONS__. Undef here to avoid clash
+// with PC member of class _Jv_BytecodeVerifier below.
+#undef PC
+
#ifdef INTERPRETER
#include <java/lang/Class.h>
#endif /* VERIFY_DEBUG */
+// This is used to mark states which are not scheduled for
+// verification.
+#define INVALID_STATE ((state *) -1)
+
static void debug_print (const char *fmt, ...)
__attribute__ ((format (printf, 1, 2)));
static inline void
-debug_print (const char *fmt, ...)
+debug_print (MAYBE_UNUSED const char *fmt, ...)
{
#ifdef VERIFY_DEBUG
va_list ap;
#endif /* VERIFY_DEBUG */
}
+// This started as a fairly ordinary verifier, and for the most part
+// it remains so. It works in the obvious way, by modeling the effect
+// of each opcode as it is encountered. For most opcodes, this is a
+// straightforward operation.
+//
+// This verifier does not do type merging. It used to, but this
+// results in difficulty verifying some relatively simple code
+// involving interfaces, and it pushed some verification work into the
+// interpreter.
+//
+// Instead of merging reference types, when we reach a point where two
+// flows of control merge, we simply keep the union of reference types
+// from each branch. Then, when we need to verify a fact about a
+// reference on the stack (e.g., that it is compatible with the
+// argument type of a method), we check to ensure that all possible
+// types satisfy the requirement.
+//
+// Another area this verifier differs from the norm is in its handling
+// of subroutines. The JVM specification has some confusing things to
+// say about subroutines. For instance, it makes claims about not
+// allowing subroutines to merge and it rejects recursive subroutines.
+// For the most part these are red herrings; we used to try to follow
+// these things but they lead to problems. For example, the notion of
+// "being in a subroutine" is not well-defined: is an exception
+// handler in a subroutine? If you never execute the `ret' but
+// instead `goto 1' do you remain in the subroutine?
+//
+// For clarity on what is really required for type safety, read
+// "Simple Verification Technique for Complex Java Bytecode
+// Subroutines" by Alessandro Coglio. Among other things this paper
+// shows that recursive subroutines are not harmful to type safety.
+// We implement something similar to what he proposes. Note that this
+// means that this verifier will accept code that is rejected by some
+// other verifiers.
+//
+// For those not wanting to read the paper, the basic observation is
+// that we can maintain split states in subroutines. We maintain one
+// state for each calling `jsr'. In other words, we re-verify a
+// subroutine once for each caller, using the exact types held by the
+// callers (as opposed to the old approach of merging types and
+// keeping a bitmap registering what did or did not change). This
+// approach lets us continue to verify correctly even when a
+// subroutine is exited via `goto' or `athrow' and not `ret'.
+//
+// In some other areas the JVM specification is (mildly) incorrect,
+// but we still implement what is specified. For instance, you cannot
+// violate type safety by allocating an object with `new' and then
+// failing to initialize it, no matter how one branches or where one
+// stores the uninitialized reference. See "Improving the official
+// specification of Java bytecode verification" by Alessandro Coglio.
+// Similarly, there's no real point in enforcing that padding bytes or
+// the mystery byte of invokeinterface must be 0, but we do that too.
+//
+// The verifier is currently neither completely lazy nor eager when it
+// comes to loading classes. It tries to represent types by name when
+// possible, and then loads them when it needs to verify a fact about
+// the type. Checking types by name is valid because we only use
+// names which come from the current class' constant pool. Since all
+// such names are looked up using the same class loader, there is no
+// danger that we might be fooled into comparing different types with
+// the same name.
+//
+// In the future we plan to allow for a completely lazy mode of
+// operation, where the verifier will construct a list of type
+// assertions to be checked later.
+//
+// Some test cases for the verifier live in the "verify" module of the
+// Mauve test suite. However, some of these are presently
+// (2004-01-20) believed to be incorrect. (More precisely the notion
+// of "correct" is not well-defined, and this verifier differs from
+// others while remaining type-safe.) Some other tests live in the
+// libgcj test suite.
class _Jv_BytecodeVerifier
{
private:
struct state;
struct type;
- struct subr_info;
- struct subr_entry_info;
struct linked_utf8;
struct ref_intersection;
+ template<typename T>
+ struct linked
+ {
+ T *val;
+ linked<T> *next;
+ };
+
// The current PC.
int PC;
// The PC corresponding to the start of the current instruction.
// The current state of the stack, locals, etc.
state *current_state;
- // We store the state at branch targets, for merging. This holds
- // such states.
- state **states;
+ // At each branch target we keep a linked list of all the states we
+ // can process at that point. We'll only have multiple states at a
+ // given PC if they both have different return-address types in the
+ // same stack or local slot. This array is indexed by PC and holds
+ // the list of all such states.
+ linked<state> **states;
- // We keep a linked list of all the PCs which we must reverify.
- // The link is done using the PC values. This is the head of the
- // list.
- int next_verify_pc;
+ // We keep a linked list of all the states which we must reverify.
+ // This is the head of the list.
+ state *next_verify_state;
// We keep some flags for each instruction. The values are the
- // FLAG_* constants defined above.
+ // FLAG_* constants defined above. This is an array indexed by PC.
char *flags;
- // We need to keep track of which instructions can call a given
- // subroutine. FIXME: this is inefficient. We keep a linked list
- // of all calling `jsr's at at each jsr target.
- subr_info **jsr_ptrs;
-
- // We keep a linked list of entries which map each `ret' instruction
- // to its unique subroutine entry point. We expect that there won't
- // be many `ret' instructions, so a linked list is ok.
- subr_entry_info *entry_points;
-
// The bytecode itself.
unsigned char *bytecode;
// The exceptions.
// A linked list of utf8 objects we allocate. This is really ugly,
// but without this our utf8 objects would be collected.
- linked_utf8 *utf8_list;
+ linked<_Jv_Utf8Const> *utf8_list;
// A linked list of all ref_intersection objects we allocate.
ref_intersection *isect_list;
- struct linked_utf8
- {
- _Jv_Utf8Const *val;
- linked_utf8 *next;
- };
-
+ // Create a new Utf-8 constant and return it. We do this to avoid
+ // having our Utf-8 constants prematurely collected. FIXME this is
+ // ugly.
_Jv_Utf8Const *make_utf8_const (char *s, int len)
{
_Jv_Utf8Const *val = _Jv_makeUtf8Const (s, len);
r->hash = val->hash;
memcpy (r->data, val->data, val->length + 1);
- linked_utf8 *lu = (linked_utf8 *) _Jv_Malloc (sizeof (linked_utf8));
+ linked<_Jv_Utf8Const> *lu
+ = (linked<_Jv_Utf8Const> *) _Jv_Malloc (sizeof (linked<_Jv_Utf8Const>));
lu->val = r;
lu->next = utf8_list;
utf8_list = lu;
// to indicate an unusable value.
unsuitable_type,
return_address_type,
+ // This is the second word of a two-word value, i.e., a double or
+ // a long.
continuation_type,
- // There is an obscure special case which requires us to note when
- // a local variable has not been used by a subroutine. See
- // push_jump_merge for more information.
- unused_by_subroutine_type,
-
// Everything after `reference_type' must be a reference type.
reference_type,
null_type,
return false;
}
- // This is used to keep track of which `jsr's correspond to a given
- // jsr target.
- struct subr_info
- {
- // PC of the instruction just after the jsr.
- int pc;
- // Link.
- subr_info *next;
- };
-
- // This is used to keep track of which subroutine entry point
- // corresponds to which `ret' instruction.
- struct subr_entry_info
- {
- // PC of the subroutine entry point.
- int pc;
- // PC of the `ret' instruction.
- int ret_pc;
- // Link.
- subr_entry_info *next;
- };
-
// The `type' class is used to represent a single type in the
// verifier.
struct type
// For reference types, the representation of the type.
ref_intersection *klass;
- // This is used when constructing a new object. It is the PC of the
+ // This is used in two situations.
+ //
+ // First, when constructing a new object, it is the PC of the
// `new' instruction which created the object. We use the special
- // value -2 to mean that this is uninitialized, and the special
- // value -1 for the case where the current method is itself the
- // <init> method.
+ // value UNINIT to mean that this is uninitialized, and the
+ // special value SELF for the case where the current method is
+ // itself the <init> method.
+ //
+ // Second, when the key is return_address_type, this holds the PC
+ // of the instruction following the `jsr'.
int pc;
static const int UNINIT = -2;
}
}
+ // Mark this type as a particular return address.
+ void set_return_address (int npc)
+ {
+ pc = npc;
+ }
+
+ // Return true if this type and type OTHER are considered
+ // mergeable for the purposes of state merging. This is related
+ // to subroutine handling. For this purpose two types are
+ // considered unmergeable if they are both return-addresses but
+ // have different PCs.
+ bool state_mergeable_p (const type &other) const
+ {
+ return (key != return_address_type
+ || other.key != return_address_type
+ || pc == other.pc);
+ }
// Return true if an object of type K can be assigned to a variable
// of type *THIS. Handle various special cases too. Might modify
{
// The way this is written, we don't need to check isarray().
if (key != reference_type)
- verifier->verify_fail ("internal error in verify_dimensions: not a reference type");
+ verifier->verify_fail ("internal error in verify_dimensions:"
+ " not a reference type");
if (klass->count_dimensions () < ndims)
- verifier->verify_fail ("array type has fewer dimensions than required");
+ verifier->verify_fail ("array type has fewer dimensions"
+ " than required");
}
- // Merge OLD_TYPE into this. On error throw exception.
+ // Merge OLD_TYPE into this. On error throw exception. Return
+ // true if the merge caused a type change.
bool merge (type& old_type, bool local_semantics,
_Jv_BytecodeVerifier *verifier)
{
{
if (local_semantics)
{
- // If we're merging into an "unused" slot, then we
- // simply accept whatever we're merging from.
- if (key == unused_by_subroutine_type)
- {
- *this = old_type;
- changed = true;
- }
- else if (old_type.key == unused_by_subroutine_type)
- {
- // Do nothing.
- }
// If we already have an `unsuitable' type, then we
// don't need to change again.
- else if (key != unsuitable_type)
+ if (key != unsuitable_type)
{
key = unsuitable_type;
changed = true;
case unsuitable_type: c = '-'; break;
case return_address_type: c = 'r'; break;
case continuation_type: c = '+'; break;
- case unused_by_subroutine_type: c = '_'; break;
case reference_type: c = 'L'; break;
case null_type: c = '@'; break;
case uninitialized_reference_type: c = 'U'; break;
type *stack;
// The local variables.
type *locals;
- // Flags are used in subroutines to keep track of which local
- // variables have been accessed. They are also used after
- char *flags;
- // If not 0, then we are in a subroutine. The value is the PC of
- // the subroutine's entry point. We can use 0 as an exceptional
- // value because PC=0 can never be a subroutine.
- int subroutine;
- // This is used to keep a linked list of all the states which
- // require re-verification. We use the PC to keep track.
- int next;
// We keep track of the type of `this' specially. This is used to
// ensure that an instance initializer invokes another initializer
// on `this' before returning. We must keep track of this
// assigns to locals[0] (overwriting `this') and then returns
// without really initializing.
type this_type;
- // This is a list of all subroutines that have been seen at this
- // point. Ordinarily this is NULL; it is only allocated and used
- // in relatively weird situations involving non-ret exit from a
- // subroutine. We have to keep track of this in this way to avoid
- // endless recursion in these cases.
- subr_info *seen_subrs;
-
- // INVALID marks a state which is not on the linked list of states
- // requiring reverification.
- static const int INVALID = -1;
- // NO_NEXT marks the state at the end of the reverification list.
- static const int NO_NEXT = -2;
-
- // This is used to mark the stack depth at the instruction just
- // after a `jsr' when we haven't yet processed the corresponding
- // `ret'. See handle_jsr_insn for more information.
- static const int NO_STACK = -1;
-
- // This flag indicates that the local was changed in this
- // subroutine.
- static const int FLAG_CHANGED = 1;
- // This is set only on the flags of the state of an instruction
- // directly following a "jsr". It indicates that the local
- // variable was changed by the subroutine corresponding to the
- // "jsr".
- static const int FLAG_USED = 2;
+
+ // The PC for this state. This is only valid on states which are
+ // permanently attached to a given PC. For an object like
+ // `current_state', which is used transiently, this has no
+ // meaning.
+ int pc;
+ // We keep a linked list of all states requiring reverification.
+ // If this is the special value INVALID_STATE then this state is
+ // not on the list. NULL marks the end of the linked list.
+ state *next;
+
+ // NO_NEXT is the PC value meaning that a new state must be
+ // acquired from the verification list.
+ static const int NO_NEXT = -1;
state ()
: this_type ()
{
stack = NULL;
locals = NULL;
- flags = NULL;
- seen_subrs = NULL;
+ next = INVALID_STATE;
}
state (int max_stack, int max_locals)
for (int i = 0; i < max_stack; ++i)
stack[i] = unsuitable_type;
locals = new type[max_locals];
- flags = (char *) _Jv_Malloc (sizeof (char) * max_locals);
- seen_subrs = NULL;
for (int i = 0; i < max_locals; ++i)
- {
- locals[i] = unsuitable_type;
- flags[i] = 0;
- }
- next = INVALID;
- subroutine = 0;
+ locals[i] = unsuitable_type;
+ pc = NO_NEXT;
+ next = INVALID_STATE;
}
- state (const state *orig, int max_stack, int max_locals,
- bool ret_semantics = false)
+ state (const state *orig, int max_stack, int max_locals)
{
stack = new type[max_stack];
locals = new type[max_locals];
- flags = (char *) _Jv_Malloc (sizeof (char) * max_locals);
- seen_subrs = NULL;
- copy (orig, max_stack, max_locals, ret_semantics);
- next = INVALID;
+ copy (orig, max_stack, max_locals);
+ pc = NO_NEXT;
+ next = INVALID_STATE;
}
~state ()
delete[] stack;
if (locals)
delete[] locals;
- if (flags)
- _Jv_Free (flags);
- clean_subrs ();
}
void *operator new[] (size_t bytes)
_Jv_Free (mem);
}
- void clean_subrs ()
- {
- subr_info *info = seen_subrs;
- while (info != NULL)
- {
- subr_info *next = info->next;
- _Jv_Free (info);
- info = next;
- }
- seen_subrs = NULL;
- }
-
- void copy (const state *copy, int max_stack, int max_locals,
- bool ret_semantics = false)
+ void copy (const state *copy, int max_stack, int max_locals)
{
stacktop = copy->stacktop;
stackdepth = copy->stackdepth;
- subroutine = copy->subroutine;
for (int i = 0; i < max_stack; ++i)
stack[i] = copy->stack[i];
for (int i = 0; i < max_locals; ++i)
- {
- // See push_jump_merge to understand this case.
- if (ret_semantics)
- {
- if ((copy->flags[i] & FLAG_CHANGED))
- {
- // Changed in the subroutine, so we copy it here.
- locals[i] = copy->locals[i];
- flags[i] |= FLAG_USED;
- }
- else
- {
- // Not changed in the subroutine. Use a special
- // type so the coming merge will overwrite.
- locals[i] = type (unused_by_subroutine_type);
- }
- }
- else
- locals[i] = copy->locals[i];
-
- // Clear the flag unconditionally just so printouts look ok,
- // then only set it if we're still in a subroutine and it
- // did in fact change.
- flags[i] &= ~FLAG_CHANGED;
- if (subroutine && (copy->flags[i] & FLAG_CHANGED) != 0)
- flags[i] |= FLAG_CHANGED;
- }
-
- clean_subrs ();
- if (copy->seen_subrs)
- {
- for (subr_info *info = copy->seen_subrs;
- info != NULL; info = info->next)
- add_subr (info->pc);
- }
+ locals[i] = copy->locals[i];
this_type = copy->this_type;
- // Don't modify `next'.
+ // Don't modify `next' or `pc'.
}
// Modify this state to reflect entry to an exception handler.
stack[i] = unsuitable_type;
}
- // Modify this state to reflect entry into a subroutine.
- void enter_subroutine (int npc, int max_locals)
+ inline int get_pc () const
{
- subroutine = npc;
- // Mark all items as unchanged. Each subroutine needs to keep
- // track of its `changed' state independently. In the case of
- // nested subroutines, this information will be merged back into
- // parent by the `ret'.
- for (int i = 0; i < max_locals; ++i)
- flags[i] &= ~FLAG_CHANGED;
+ return pc;
}
- // Indicate that we've been in this this subroutine.
- void add_subr (int pc)
+ void set_pc (int npc)
{
- subr_info *n = (subr_info *) _Jv_Malloc (sizeof (subr_info));
- n->pc = pc;
- n->next = seen_subrs;
- seen_subrs = n;
+ pc = npc;
}
// Merge STATE_OLD into this state. Destructively modifies this
// state. Returns true if the new state was in fact changed.
// Will throw an exception if the states are not mergeable.
- bool merge (state *state_old, bool ret_semantics,
- int max_locals, _Jv_BytecodeVerifier *verifier,
- bool jsr_semantics = false)
+ bool merge (state *state_old, int max_locals,
+ _Jv_BytecodeVerifier *verifier)
{
bool changed = false;
if (this_type.isinitialized ())
this_type = state_old->this_type;
- // Merge subroutine states. Here we just keep track of what
- // subroutine we think we're in. We only check for a merge
- // (which is invalid) when we see a `ret'.
- if (subroutine == state_old->subroutine)
- {
- // Nothing.
- }
- else if (subroutine == 0)
- {
- subroutine = state_old->subroutine;
- changed = true;
- }
- else
- {
- // If the subroutines differ, and we haven't seen this
- // subroutine before, indicate that the state changed. This
- // is needed to detect when subroutines have merged.
- bool found = false;
- for (subr_info *info = seen_subrs; info != NULL; info = info->next)
- {
- if (info->pc == state_old->subroutine)
- {
- found = true;
- break;
- }
- }
- if (! found)
- {
- add_subr (state_old->subroutine);
- changed = true;
- }
- }
-
- // Merge stacks, including special handling for NO_STACK case.
- // If the destination is NO_STACK, this means it is the
- // instruction following a "jsr" and has not yet been processed
- // in any way. In this situation, if we are currently
- // processing a "ret", then we must *copy* any locals changed in
- // the subroutine into the current state. Merging in this
- // situation is incorrect because the locals we've noted didn't
- // come real program flow, they are just an artifact of how
- // we've chosen to handle the post-jsr state.
- bool copy_in_locals = ret_semantics && stacktop == NO_STACK;
-
- if (state_old->stacktop == NO_STACK)
- {
- // This can happen if we're doing a pass-through jsr merge.
- // Here we can just ignore the stack.
- }
- else if (stacktop == NO_STACK)
- {
- stacktop = state_old->stacktop;
- stackdepth = state_old->stackdepth;
- for (int i = 0; i < stacktop; ++i)
- stack[i] = state_old->stack[i];
- changed = true;
- }
- else if (state_old->stacktop != stacktop)
+ // Merge stacks.
+ if (state_old->stacktop != stacktop) // FIXME stackdepth instead?
verifier->verify_fail ("stack sizes differ");
- else
+ for (int i = 0; i < state_old->stacktop; ++i)
{
- for (int i = 0; i < state_old->stacktop; ++i)
- {
- if (stack[i].merge (state_old->stack[i], false, verifier))
- changed = true;
- }
+ if (stack[i].merge (state_old->stack[i], false, verifier))
+ changed = true;
}
// Merge local variables.
for (int i = 0; i < max_locals; ++i)
{
- // If we're not processing a `ret', then we merge every
- // local variable. If we are processing a `ret', then we
- // only merge locals which changed in the subroutine. When
- // processing a `ret', STATE_OLD is the state at the point
- // of the `ret', and THIS is the state just after the `jsr'.
- // See comment above for explanation of COPY_IN_LOCALS.
- if (copy_in_locals)
- {
- if ((state_old->flags[i] & FLAG_CHANGED) != 0)
- {
- locals[i] = state_old->locals[i];
- changed = true;
- // There's no point in calling note_variable here,
- // since we call it under the same condition before
- // the loop ends.
- }
- }
- else if (jsr_semantics && (flags[i] & FLAG_USED) != 0)
- {
- // We are processing the "pass-through" part of a jsr
- // statement. In this particular case, the local was
- // changed by the subroutine. So, we have no work to
- // do, as the pre-jsr value does not survive the
- // subroutine call.
- }
- else if (! ret_semantics
- || (state_old->flags[i] & FLAG_CHANGED) != 0)
- {
- // If we have ordinary (not ret) semantics, then we have
- // merging flow control, so we merge types. Or, we have
- // jsr pass-through semantics and the type survives the
- // subroutine (see above), so again we merge. Or,
- // finally, we have ret semantics and this value did
- // change, in which case we merge the change from the
- // subroutine into the post-jsr instruction.
- if (locals[i].merge (state_old->locals[i], true, verifier))
- {
- // Note that we don't call `note_variable' here.
- // This change doesn't represent a real change to a
- // local, but rather a merge artifact. If we're in
- // a subroutine which is called with two
- // incompatible types in a slot that is unused by
- // the subroutine, then we don't want to mark that
- // variable as having been modified.
- changed = true;
- }
- }
-
- // If we're in a subroutine, we must compute the union of
- // all the changed local variables.
- if ((state_old->flags[i] & FLAG_CHANGED) != 0)
- note_variable (i);
-
- // If we're returning from a subroutine, we must mark the
- // post-jsr instruction with information about what changed,
- // so that future "pass-through" jsr merges work correctly.
- if (ret_semantics && (state_old->flags[i] & FLAG_CHANGED) != 0)
- flags[i] |= FLAG_USED;
+ if (locals[i].merge (state_old->locals[i], true, verifier))
+ changed = true;
}
return changed;
this_type = k;
}
- // Note that a local variable was modified.
- void note_variable (int index)
- {
- if (subroutine > 0)
- flags[index] |= FLAG_CHANGED;
- }
-
// Mark each `new'd object we know of that was allocated at PC as
// initialized.
void set_initialized (int pc, int max_locals)
this_type.set_initialized (pc);
}
- // Return true if this state is the unmerged result of a `ret'.
- bool is_unmerged_ret_state (int max_locals) const
+ // This tests to see whether two states can be considered "merge
+ // compatible". If both states have a return-address in the same
+ // slot, and the return addresses are different, then they are not
+ // compatible and we must not try to merge them.
+ bool state_mergeable_p (state *other, int max_locals,
+ _Jv_BytecodeVerifier *verifier)
{
- if (stacktop == NO_STACK)
- return true;
+ // This is tricky: if the stack sizes differ, then not only are
+ // these not mergeable, but in fact we should give an error, as
+ // we've found two execution paths that reach a branch target
+ // with different stack depths. FIXME stackdepth instead?
+ if (stacktop != other->stacktop)
+ verifier->verify_fail ("stack sizes differ");
+
+ for (int i = 0; i < stacktop; ++i)
+ if (! stack[i].state_mergeable_p (other->stack[i]))
+ return false;
for (int i = 0; i < max_locals; ++i)
+ if (! locals[i].state_mergeable_p (other->locals[i]))
+ return false;
+ return true;
+ }
+
+ void reverify (_Jv_BytecodeVerifier *verifier)
+ {
+ if (next == INVALID_STATE)
{
- if (locals[i].key == unused_by_subroutine_type)
- return true;
+ next = verifier->next_verify_state;
+ verifier->next_verify_state = this;
}
- return false;
}
#ifdef VERIFY_DEBUG
debug_print (".");
debug_print (" [local] ");
for (i = 0; i < max_locals; ++i)
- {
- locals[i].print ();
- if ((flags[i] & FLAG_USED) != 0)
- debug_print ((flags[i] & FLAG_CHANGED) ? ">" : "<");
- else
- debug_print ((flags[i] & FLAG_CHANGED) ? "+" : " ");
- }
- if (subroutine == 0)
- debug_print (" | None");
- else
- debug_print (" | %4d", subroutine);
+ locals[i].print ();
debug_print (" | %p\n", this);
}
#else
if (index > current_method->max_locals - depth)
verify_fail ("invalid local variable");
current_state->locals[index] = t;
- current_state->note_variable (index);
if (depth == 2)
- {
- current_state->locals[index + 1] = continuation_type;
- current_state->note_variable (index + 1);
- }
+ current_state->locals[index + 1] = continuation_type;
if (index > 0 && current_state->locals[index - 1].iswide ())
- {
- current_state->locals[index - 1] = unsuitable_type;
- // There's no need to call note_variable here.
- }
+ current_state->locals[index - 1] = unsuitable_type;
}
type get_variable (int index, type t)
return npc;
}
+ // Add a new state to the state list at NPC.
+ state *add_new_state (int npc, state *old_state)
+ {
+ state *new_state = new state (old_state, current_method->max_stack,
+ current_method->max_locals);
+ debug_print ("== New state in add_new_state\n");
+ new_state->print ("New", npc, current_method->max_stack,
+ current_method->max_locals);
+ linked<state> *nlink
+ = (linked<state> *) _Jv_Malloc (sizeof (linked<state>));
+ nlink->val = new_state;
+ nlink->next = states[npc];
+ states[npc] = nlink;
+ new_state->set_pc (npc);
+ return new_state;
+ }
+
// Merge the indicated state into the state at the branch target and
- // schedule a new PC if there is a change. If RET_SEMANTICS is
- // true, then we are merging from a `ret' instruction into the
- // instruction after a `jsr'. This is a special case with its own
- // modified semantics. If JSR_SEMANTICS is true, then we're merging
- // some type information from a "jsr" instruction to the immediately
- // following instruction. In this situation we have to be careful
- // not to merge local variables whose values are modified by the
- // subroutine we're about to call.
- void push_jump_merge (int npc, state *nstate,
- bool ret_semantics = false,
- bool jsr_semantics = false)
+ // schedule a new PC if there is a change. NPC is the PC of the
+ // branch target, and FROM_STATE is the state at the source of the
+ // branch. This method returns true if the destination state
+ // changed and requires reverification, false otherwise.
+ void merge_into (int npc, state *from_state)
{
- bool changed = true;
- if (states[npc] == NULL)
- {
- // There's a weird situation here. If are examining the
- // branch that results from a `ret', and there is not yet a
- // state available at the branch target (the instruction just
- // after the `jsr'), then we have to construct a special kind
- // of state at that point for future merging. This special
- // state has the type `unused_by_subroutine_type' in each slot
- // which was not modified by the subroutine.
- states[npc] = new state (nstate, current_method->max_stack,
- current_method->max_locals, ret_semantics);
- debug_print ("== New state in push_jump_merge (ret_semantics = %s)\n",
- ret_semantics ? "true" : "false");
- states[npc]->print ("New", npc, current_method->max_stack,
- current_method->max_locals);
- }
- else
+ // Iterate over all target states and merge our state into each,
+ // if applicable. FIXME one improvement we could make here is
+ // "state destruction". Merging a new state into an existing one
+ // might cause a return_address_type to be merged to
+ // unsuitable_type. In this case the resulting state may now be
+ // mergeable with other states currently held in parallel at this
+ // location. So in this situation we could pairwise compare and
+ // reduce the number of parallel states.
+ bool applicable = false;
+ for (linked<state> *iter = states[npc]; iter != NULL; iter = iter->next)
{
- debug_print ("== Merge states in push_jump_merge\n");
- nstate->print ("Frm", start_PC, current_method->max_stack,
- current_method->max_locals);
- states[npc]->print (" To", npc, current_method->max_stack,
- current_method->max_locals);
- changed = states[npc]->merge (nstate, ret_semantics,
- current_method->max_locals, this,
- jsr_semantics);
- states[npc]->print ("New", npc, current_method->max_stack,
- current_method->max_locals);
+ state *new_state = iter->val;
+ if (new_state->state_mergeable_p (from_state,
+ current_method->max_locals, this))
+ {
+ applicable = true;
+
+ debug_print ("== Merge states in merge_into\n");
+ from_state->print ("Frm", start_PC, current_method->max_stack,
+ current_method->max_locals);
+ new_state->print (" To", npc, current_method->max_stack,
+ current_method->max_locals);
+ bool changed = new_state->merge (from_state,
+ current_method->max_locals,
+ this);
+ new_state->print ("New", npc, current_method->max_stack,
+ current_method->max_locals);
+
+ if (changed)
+ new_state->reverify (this);
+ }
}
- if (changed && states[npc]->next == state::INVALID)
+ if (! applicable)
{
- // The merge changed the state, and the new PC isn't yet on our
- // list of PCs to re-verify.
- states[npc]->next = next_verify_pc;
- next_verify_pc = npc;
+ // Either we don't yet have a state at NPC, or we have a
+ // return-address type that is in conflict with all existing
+ // state. So, we need to create a new entry.
+ state *new_state = add_new_state (npc, from_state);
+ // A new state added in this way must always be reverified.
+ new_state->reverify (this);
}
}
int npc = compute_jump (offset);
if (npc < PC)
current_state->check_no_uninitialized_objects (current_method->max_locals, this);
- push_jump_merge (npc, current_state);
+ merge_into (npc, current_state);
}
void push_exception_jump (type t, int pc)
if (current_method->max_stack < 1)
verify_fail ("stack overflow at exception handler");
s.set_exception (t, current_method->max_stack);
- push_jump_merge (pc, &s);
+ merge_into (pc, &s);
}
- int pop_jump ()
+ state *pop_jump ()
{
- int *prev_loc = &next_verify_pc;
- int npc = next_verify_pc;
-
- while (npc != state::NO_NEXT)
+ state *new_state = next_verify_state;
+ if (new_state == INVALID_STATE)
+ verify_fail ("programmer error in pop_jump");
+ if (new_state != NULL)
{
- // If the next available PC is an unmerged `ret' state, then
- // we aren't yet ready to handle it. That's because we would
- // need all kind of special cases to do so. So instead we
- // defer this jump until after we've processed it via a
- // fall-through. This has to happen because the instruction
- // before this one must be a `jsr'.
- if (! states[npc]->is_unmerged_ret_state (current_method->max_locals))
- {
- *prev_loc = states[npc]->next;
- states[npc]->next = state::INVALID;
- return npc;
- }
-
- prev_loc = &states[npc]->next;
- npc = states[npc]->next;
+ next_verify_state = new_state->next;
+ new_state->next = INVALID_STATE;
}
-
- // Note that we might have gotten here even when there are
- // remaining states to process. That can happen if we find a
- // `jsr' without a `ret'.
- return state::NO_NEXT;
+ return new_state;
}
void invalidate_pc ()
PC = state::NO_NEXT;
}
- void note_branch_target (int pc, bool is_jsr_target = false)
+ void note_branch_target (int pc)
{
// Don't check `pc <= PC', because we've advanced PC after
// fetching the target and we haven't yet checked the next
if (pc < PC && ! (flags[pc] & FLAG_INSN_START))
verify_fail ("branch not to instruction start", start_PC);
flags[pc] |= FLAG_BRANCH_TARGET;
- if (is_jsr_target)
- {
- // Record the jsr which called this instruction.
- subr_info *info = (subr_info *) _Jv_Malloc (sizeof (subr_info));
- info->pc = PC;
- info->next = jsr_ptrs[pc];
- jsr_ptrs[pc] = info;
- }
}
void skip_padding ()
verify_fail ("found nonzero padding byte");
}
- // Return the subroutine to which the instruction at PC belongs.
- int get_subroutine (int pc)
- {
- if (states[pc] == NULL)
- return 0;
- return states[pc]->subroutine;
- }
-
// Do the work for a `ret' instruction. INDEX is the index into the
// local variables.
void handle_ret_insn (int index)
{
- get_variable (index, return_address_type);
-
- int csub = current_state->subroutine;
- if (csub == 0)
- verify_fail ("no subroutine");
-
- // Check to see if we've merged subroutines.
- subr_entry_info *entry;
- for (entry = entry_points; entry != NULL; entry = entry->next)
- {
- if (entry->ret_pc == start_PC)
- break;
- }
- if (entry == NULL)
- {
- entry = (subr_entry_info *) _Jv_Malloc (sizeof (subr_entry_info));
- entry->pc = csub;
- entry->ret_pc = start_PC;
- entry->next = entry_points;
- entry_points = entry;
- }
- else if (entry->pc != csub)
- verify_fail ("subroutines merged");
-
- for (subr_info *subr = jsr_ptrs[csub]; subr != NULL; subr = subr->next)
- {
- // We might be returning to a `jsr' that is at the end of the
- // bytecode. This is ok if we never return from the called
- // subroutine, but if we see this here it is an error.
- if (subr->pc >= current_method->code_length)
- verify_fail ("fell off end");
+ type ret_addr = get_variable (index, return_address_type);
+ // It would be nice if we could do this. However, the JVM Spec
+ // doesn't say that this is what happens. It is implied that
+ // reusing a return address is invalid, but there's no actual
+ // prohibition against it.
+ // set_variable (index, unsuitable_type);
+
+ int npc = ret_addr.get_pc ();
+ // We might be returning to a `jsr' that is at the end of the
+ // bytecode. This is ok if we never return from the called
+ // subroutine, but if we see this here it is an error.
+ if (npc >= current_method->code_length)
+ verify_fail ("fell off end");
- // Temporarily modify the current state so it looks like we're
- // in the enclosing context.
- current_state->subroutine = get_subroutine (subr->pc);
- if (subr->pc < PC)
- current_state->check_no_uninitialized_objects (current_method->max_locals, this);
- push_jump_merge (subr->pc, current_state, true);
- }
-
- current_state->subroutine = csub;
+ if (npc < PC)
+ current_state->check_no_uninitialized_objects (current_method->max_locals,
+ this);
+ merge_into (npc, current_state);
invalidate_pc ();
}
- // We're in the subroutine SUB, calling a subroutine at DEST. Make
- // sure this subroutine isn't already on the stack.
- void check_nonrecursive_call (int sub, int dest)
- {
- if (sub == 0)
- return;
- if (sub == dest)
- verify_fail ("recursive subroutine call");
- for (subr_info *info = jsr_ptrs[sub]; info != NULL; info = info->next)
- check_nonrecursive_call (get_subroutine (info->pc), dest);
- }
-
void handle_jsr_insn (int offset)
{
int npc = compute_jump (offset);
if (npc < PC)
current_state->check_no_uninitialized_objects (current_method->max_locals, this);
- check_nonrecursive_call (current_state->subroutine, npc);
// Modify our state as appropriate for entry into a subroutine.
- push_type (return_address_type);
- push_jump_merge (npc, current_state);
- // Clean up.
- pop_type (return_address_type);
-
- // On entry to the subroutine, the subroutine number must be set
- // and the locals must be marked as cleared. We do this after
- // merging state so that we don't erroneously "notice" a variable
- // change merely on entry.
- states[npc]->enter_subroutine (npc, current_method->max_locals);
-
- // Indicate that we don't know the stack depth of the instruction
- // following the `jsr'. The idea here is that we need to merge
- // the local variable state across the jsr, but the subroutine
- // might change the stack depth, so we can't make any assumptions
- // about it. So we have yet another special case. We know that
- // at this point PC points to the instruction after the jsr. Note
- // that it is ok to have a `jsr' at the end of the bytecode,
- // provided that the called subroutine never returns. So, we have
- // a special case here and another one when we handle the ret.
- if (PC < current_method->code_length)
- {
- current_state->stacktop = state::NO_STACK;
- push_jump_merge (PC, current_state, false, true);
- }
+ type ret_addr (return_address_type);
+ ret_addr.set_return_address (PC);
+ push_type (ret_addr);
+ merge_into (npc, current_state);
invalidate_pc ();
}
case unsuitable_type:
case return_address_type:
case continuation_type:
- case unused_by_subroutine_type:
case reference_type:
case null_type:
case uninitialized_reference_type:
void branch_prepass ()
{
flags = (char *) _Jv_Malloc (current_method->code_length);
- jsr_ptrs = (subr_info **) _Jv_Malloc (sizeof (subr_info *)
- * current_method->code_length);
for (int i = 0; i < current_method->code_length; ++i)
- {
- flags[i] = 0;
- jsr_ptrs[i] = NULL;
- }
-
- bool last_was_jsr = false;
+ flags[i] = 0;
PC = 0;
while (PC < current_method->code_length)
start_PC = PC;
flags[PC] |= FLAG_INSN_START;
- // If the previous instruction was a jsr, then the next
- // instruction is a branch target -- the branch being the
- // corresponding `ret'.
- if (last_was_jsr)
- note_branch_target (PC);
- last_was_jsr = false;
-
java_opcode opcode = (java_opcode) bytecode[PC++];
switch (opcode)
{
break;
case op_jsr:
- last_was_jsr = true;
- // Fall through.
case op_ifeq:
case op_ifne:
case op_iflt:
case op_ifnull:
case op_ifnonnull:
case op_goto:
- note_branch_target (compute_jump (get_short ()), last_was_jsr);
+ note_branch_target (compute_jump (get_short ()));
break;
case op_tableswitch:
break;
case op_jsr_w:
- last_was_jsr = true;
- // Fall through.
case op_goto_w:
- note_branch_target (compute_jump (get_int ()), last_was_jsr);
+ note_branch_target (compute_jump (get_int ()));
break;
// These are unused here, but we call them out explicitly
// True if we are verifying an instance initializer.
bool this_is_init = initialize_stack ();
- states = (state **) _Jv_Malloc (sizeof (state *)
- * current_method->code_length);
+ states = (linked<state> **) _Jv_Malloc (sizeof (linked<state> *)
+ * current_method->code_length);
for (int i = 0; i < current_method->code_length; ++i)
states[i] = NULL;
- next_verify_pc = state::NO_NEXT;
+ next_verify_state = NULL;
while (true)
{
// If the PC was invalidated, get a new one from the work list.
if (PC == state::NO_NEXT)
{
- PC = pop_jump ();
- if (PC == state::INVALID)
- verify_fail ("can't happen: saw state::INVALID");
- if (PC == state::NO_NEXT)
+ state *new_state = pop_jump ();
+ // If it is null, we're done.
+ if (new_state == NULL)
break;
+
+ PC = new_state->get_pc ();
debug_print ("== State pop from pending list\n");
// Set up the current state.
- current_state->copy (states[PC], current_method->max_stack,
+ current_state->copy (new_state, current_method->max_stack,
current_method->max_locals);
}
else
{
- // Control can't fall off the end of the bytecode. We
- // only need to check this in the fall-through case,
- // because branch bounds are checked when they are
- // pushed.
- if (PC >= current_method->code_length)
- verify_fail ("fell off end");
-
// We only have to do this checking in the situation where
// control flow falls through from the previous
// instruction. Otherwise merging is done at the time we
if (states[PC] != NULL)
{
// We've already visited this instruction. So merge
- // the states together. If this yields no change then
- // we don't have to re-verify. However, if the new
- // state is an the result of an unmerged `ret', we
- // must continue through it.
- debug_print ("== Fall through merge\n");
- states[PC]->print ("Old", PC, current_method->max_stack,
- current_method->max_locals);
- current_state->print ("Cur", PC, current_method->max_stack,
- current_method->max_locals);
- if (! current_state->merge (states[PC], false,
- current_method->max_locals, this)
- && ! states[PC]->is_unmerged_ret_state (current_method->max_locals))
- {
- debug_print ("== Fall through optimization\n");
- invalidate_pc ();
- continue;
- }
- // Save a copy of it for later.
- states[PC]->copy (current_state, current_method->max_stack,
- current_method->max_locals);
- current_state->print ("New", PC, current_method->max_stack,
- current_method->max_locals);
+ // the states together. It is simplest, but not most
+ // efficient, to just always invalidate the PC here.
+ merge_into (PC, current_state);
+ invalidate_pc ();
+ continue;
}
}
+ // Control can't fall off the end of the bytecode. We need to
+ // check this in both cases, not just the fall-through case,
+ // because we don't check to see whether a `jsr' appears at
+ // the end of the bytecode until we process a `ret'.
+ if (PC >= current_method->code_length)
+ verify_fail ("fell off end");
+
// We only have to keep saved state at branch targets. If
// we're at a branch target and the state here hasn't been set
- // yet, we set it now.
+ // yet, we set it now. You might notice that `ret' targets
+ // won't necessarily have FLAG_BRANCH_TARGET set. This
+ // doesn't matter, since those states will be filled in by
+ // merge_into.
if (states[PC] == NULL && (flags[PC] & FLAG_BRANCH_TARGET))
- {
- states[PC] = new state (current_state, current_method->max_stack,
- current_method->max_locals);
- }
+ add_new_state (PC, current_state);
// Set this before handling exceptions so that debug output is
// sane.
states = NULL;
flags = NULL;
- jsr_ptrs = NULL;
utf8_list = NULL;
isect_list = NULL;
- entry_points = NULL;
}
~_Jv_BytecodeVerifier ()
{
- if (states)
- _Jv_Free (states);
if (flags)
_Jv_Free (flags);
- if (jsr_ptrs)
- {
- for (int i = 0; i < current_method->code_length; ++i)
- {
- if (jsr_ptrs[i] != NULL)
- {
- subr_info *info = jsr_ptrs[i];
- while (info != NULL)
- {
- subr_info *next = info->next;
- _Jv_Free (info);
- info = next;
- }
- }
- }
- _Jv_Free (jsr_ptrs);
- }
-
while (utf8_list != NULL)
{
- linked_utf8 *n = utf8_list->next;
+ linked<_Jv_Utf8Const> *n = utf8_list->next;
_Jv_Free (utf8_list->val);
_Jv_Free (utf8_list);
utf8_list = n;
}
- while (entry_points != NULL)
- {
- subr_entry_info *next = entry_points->next;
- _Jv_Free (entry_points);
- entry_points = next;
- }
-
while (isect_list != NULL)
{
ref_intersection *next = isect_list->alloc_next;
delete isect_list;
isect_list = next;
}
+
+ if (states)
+ {
+ for (int i = 0; i < current_method->code_length; ++i)
+ {
+ linked<state> *iter = states[i];
+ while (iter != NULL)
+ {
+ linked<state> *next = iter->next;
+ delete iter->val;
+ _Jv_Free (iter);
+ iter = next;
+ }
+ }
+ _Jv_Free (states);
+ }
}
};
_Jv_BytecodeVerifier v (meth);
v.verify_instructions ();
}
+
#endif /* INTERPRETER */
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