The Tor Browser: comparison xpcom/analysis/outparams.js

comparison: xpcom/analysis/outparams.js

xpcom/analysis/outparams.js

branch: TOR_BUG_3246
changeset 7: 129ffea94266

equal deleted inserted replaced

--1:000000000000
+:39bbd0ec4e60
+/* This Source Code Form is subject to the terms of the Mozilla Public
+* License, v. 2.0. If a copy of the MPL was not distributed with this
+* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+require({ version: '1.8' });
+require({ after_gcc_pass: 'cfg' });
+include('treehydra.js');
+include('util.js');
+include('gcc_util.js');
+include('gcc_print.js');
+include('unstable/adts.js');
+include('unstable/analysis.js');
+include('unstable/esp.js');
+let Zero_NonZero = {};
+include('unstable/zero_nonzero.js', Zero_NonZero);
+include('xpcom/analysis/mayreturn.js');
+function safe_location_of(t) {
+if (t === undefined)
+return UNKNOWN_LOCATION;
+return location_of(t);
+}
+MapFactory.use_injective = true;
+// Print a trace for each function analyzed
+let TRACE_FUNCTIONS = 0;
+// Trace operation of the ESP analysis, use 2 or 3 for more detail
+let TRACE_ESP = 0;
+// Trace determination of function call parameter semantics, 2 for detail
+let TRACE_CALL_SEM = 0;
+// Print time-taken stats
+let TRACE_PERF = 0;
+// Log analysis results in a special format
+let LOG_RESULTS = false;
+const WARN_ON_SET_NULL = false;
+const WARN_ON_SET_FAILURE = false;
+// Filter functions to process per CLI
+let func_filter;
+if (this.arg == undefined || this.arg == '') {
+func_filter = function(fd) true;
+} else {
+func_filter = function(fd) function_decl_name(fd) == this.arg;
+}
+function process_tree(func_decl) {
+if (!func_filter(func_decl)) return;
+// Determine outparams and return if function not relevant
+if (DECL_CONSTRUCTOR_P(func_decl)) return;
+let psem = OutparamCheck.prototype.func_param_semantics(func_decl);
+if (!psem.some(function(x) x.check)) return;
+let decl = rectify_function_decl(func_decl);
+if (decl.resultType != 'nsresult' && decl.resultType != 'PRBool' &&
+decl.resultType != 'void') {
+warning("Cannot analyze outparam usage for function with return type '" +
+decl.resultType + "'", location_of(func_decl));
+return;
+}
+let params = [ v for (v in flatten_chain(DECL_ARGUMENTS(func_decl))) ];
+let outparam_list = [];
+let psem_list = [];
+for (let i = 0; i < psem.length; ++i) {
+if (psem[i].check) {
+outparam_list.push(params[i]);
+psem_list.push(psem[i]);
+}
+}
+if (outparam_list.length == 0) return;
+// At this point we have a function we want to analyze
+let fstring = rfunc_string(decl);
+if (TRACE_FUNCTIONS) {
+print('* function ' + fstring);
+print('    ' + loc_string(location_of(func_decl)));
+}
+if (TRACE_PERF) timer_start(fstring);
+for (let i = 0; i < outparam_list.length; ++i) {
+let p = outparam_list[i];
+if (TRACE_FUNCTIONS) {
+print("  outparam " + expr_display(p) + " " + DECL_UID(p) + ' ' +
+psem_list[i].label);
+}
+}
+let cfg = function_decl_cfg(func_decl);
+let [retvar, retvars] = function() {
+let trace = 0;
+let a = new MayReturnAnalysis(cfg, trace);
+a.run();
+return [a.retvar, a.vbls];
+}();
+if (retvar == undefined && decl.resultType != 'void') throw new Error("assert");
+{
+let trace = TRACE_ESP;
+for (let i = 0; i < outparam_list.length; ++i) {
+let psem = [ psem_list[i] ];
+let outparam = [ outparam_list[i] ];
+let a = new OutparamCheck(cfg, psem, outparam, retvar, retvars, trace);
+// This is annoying, but this field is only used for logging anyway.
+a.fndecl = func_decl;
+a.run();
+a.check(decl.resultType == 'void', func_decl);
+}
+}
+if (TRACE_PERF) timer_stop(fstring);
+}
+// Outparam check analysis
+function OutparamCheck(cfg, psem_list, outparam_list, retvar, retvar_set,
+trace) {
+// We need to save the retvars so we can detect assignments through
+// their addresses passed as arguments.
+this.retvar_set = retvar_set;
+this.retvar = retvar;
+// We need both an ordered set and a lookup structure
+this.outparam_list = outparam_list
+this.outparams = create_decl_set(outparam_list);
+this.psem_list = psem_list;
+// Set up property state vars for ESP
+let psvar_list = [];
+for each (let v in outparam_list) {
+psvar_list.push(new ESP.PropVarSpec(v, true, av.NOT_WRITTEN));
+}
+for (let v in retvar_set.items()) {
+psvar_list.push(new ESP.PropVarSpec(v, v == this.retvar, ESP.TOP));
+}
+if (trace) {
+print("PS vars");
+for each (let v in this.psvar_list) {
+print("    " + expr_display(v.vbl));
+}
+}
+this.zeroNonzero = new Zero_NonZero.Zero_NonZero();
+ESP.Analysis.call(this, cfg, psvar_list, av.meet, trace);
+}
+// Abstract values for outparam check
+function AbstractValue(name, ch) {
+this.name = name;
+this.ch = ch;
+}
+AbstractValue.prototype.equals = function(v) {
+return this === v;
+}
+AbstractValue.prototype.toString = function() {
+return this.name + ' (' + this.ch + ')';
+}
+AbstractValue.prototype.toShortString = function() {
+return this.ch;
+}
+let avspec = [
+// Abstract values for outparam contents write status
+[ 'NULL',          'x' ],   // is a null pointer
+[ 'NOT_WRITTEN',   '-' ],   // not written
+[ 'WROTE_NULL',    '/' ],   // had NULL written to
+[ 'WRITTEN',       '+' ],   // had anything written to
+// MAYBE_WRITTEN is special. "Officially", it means the same thing as
+// NOT_WRITTEN. What it really means is that an outparam was passed
+// to another function as a possible outparam (outparam type, but not
+// in last position), so if there is an error with it not being written,
+// we can give a hint about the possible outparam in the warning.
+[ 'MAYBE_WRITTEN', '?' ],   // written if possible outparam is one
+];
+let av = {};
+for each (let [name, ch] in avspec) {
+av[name] = new AbstractValue(name, ch);
+}
+av.ZERO = Zero_NonZero.Lattice.ZERO;
+av.NONZERO = Zero_NonZero.Lattice.NONZERO;
+/*
+av.ZERO.negation = av.NONZERO;
+av.NONZERO.negation = av.ZERO;
+// Abstract values for int constants. We use these to figure out feasible
+// paths in the presence of GCC finally_tmp-controlled switches.
+function makeIntAV(v) {
+let key = 'int_' + v;
+if (cachedAVs.hasOwnProperty(key)) return cachedAVs[key];
+let s = "" + v;
+let ans = cachedAVs[key] = new AbstractValue(s, s);
+ans.int_val = v;
+return ans;
+}
+*/
+let cachedAVs = {};
+// Abstract values for pointers that contain a copy of an outparam
+// pointer. We use these to figure out writes to a casted copy of
+// an outparam passed to another method.
+function makeOutparamAV(v) {
+let key = 'outparam_' + DECL_UID(v);
+if (key in cachedAVs) return cachedAVs[key];
+let ans = cachedAVs[key] =
+new AbstractValue('OUTPARAM:' + expr_display(v), 'P');
+ans.outparam = v;
+return ans;
+}
+/** Return the integer value if this is an integer av, otherwise undefined. */
+av.intVal = function(v) {
+if (v.hasOwnProperty('int_val'))
+return v.int_val;
+return undefined;
+}
+/** Meet function for our abstract values. */
+av.meet = function(v1, v2) {
+// At this point we know v1 != v2.
+let values = [v1,v2]
+if (values.indexOf(av.LOCKED) != -1
+|| values.indexOf(av.UNLOCKED) != -1)
+return ESP.NOT_REACHED;
+return Zero_NonZero.meet(v1, v2)
+};
+// Outparam check analysis
+OutparamCheck.prototype = new ESP.Analysis;
+OutparamCheck.prototype.split = function(vbl, v) {
+// Can't happen for current version of ESP, but could change
+if (v != ESP.TOP) throw new Error("not implemented");
+return [ av.ZERO, av.NONZERO ];
+}
+OutparamCheck.prototype.updateEdgeState = function(e) {
+e.state.keepOnly(e.dest.keepVars);
+}
+OutparamCheck.prototype.flowState = function(isn, state) {
+switch (TREE_CODE(isn)) {
+case GIMPLE_ASSIGN:
+this.processAssign(isn, state);
+break;
+case GIMPLE_CALL:
+this.processCall(isn, isn, state);
+break;
+case GIMPLE_SWITCH:
+case GIMPLE_COND:
+// This gets handled by flowStateCond instead, has no exec effect
+break;
+default:
+this.zeroNonzero.flowState(isn, state);
+}
+}
+OutparamCheck.prototype.flowStateCond = function(isn, truth, state) {
+this.zeroNonzero.flowStateCond(isn, truth, state);
+}
+// For any outparams-specific semantics, we handle it here and then
+// return. Otherwise we delegate to the zero-nonzero analysis.
+OutparamCheck.prototype.processAssign = function(isn, state) {
+let lhs = gimple_op(isn, 0);
+let rhs = gimple_op(isn, 1);
+if (DECL_P(lhs)) {
+// Unwrap NOP_EXPR, which is semantically a copy.
+if (TREE_CODE(rhs) == NOP_EXPR) {
+rhs = rhs.operands()[0];
+}
+if (DECL_P(rhs) && this.outparams.has(rhs)) {
+// Copying an outparam pointer. We have to remember this so that
+// if it is assigned thru later, we pick up the write.
+state.assignValue(lhs, makeOutparamAV(rhs), isn);
+return;
+}
+// Cases of this switch that handle something should return from
+// the function. Anything that does not return is picked up afteward.
+switch (TREE_CODE(rhs)) {
+case INTEGER_CST:
+if (this.outparams.has(lhs)) {
+warning("assigning to outparam pointer");
+return;
+}
+break;
+case EQ_EXPR: {
+// We only care about testing outparams for NULL (and then not writing)
+let [op1, op2] = rhs.operands();
+if (DECL_P(op1) && this.outparams.has(op1) && expr_literal_int(op2) == 0) {
+state.update(function(ss) {
+let [s1, s2] = [ss, ss.copy()]; // s1 true, s2 false
+s1.assignValue(lhs, av.NONZERO, isn);
+s1.assignValue(op1, av.NULL, isn);
+s2.assignValue(lhs, av.ZERO, isn);
+return [s1, s2];
+});
+return;
+}
+}
+break;
+case CALL_EXPR:
+/* Embedded CALL_EXPRs are a 4.3 issue */
+this.processCall(rhs, isn, state, lhs);
+return;
+case INDIRECT_REF:
+// If rhs is *outparam and pointer-typed, lhs is NULL iff rhs is
+// WROTE_NULL. Required for testcase onull.cpp.
+let v = rhs.operands()[0];
+if (DECL_P(v) && this.outparams.has(v) &&
+TREE_CODE(TREE_TYPE(v)) == POINTER_TYPE) {
+state.update(function(ss) {
+let val = ss.get(v) == av.WROTE_NULL ? av.ZERO : av.NONZERO;
+ss.assignValue(lhs, val, isn);
+return [ ss ];
+});
+return;
+}
+}
+// Nothing special -- delegate
+this.zeroNonzero.processAssign(isn, state);
+return;
+}
+switch (TREE_CODE(lhs)) {
+case INDIRECT_REF:
+// Writing to an outparam. We want to try to figure out if we're
+// writing NULL.
+let e = TREE_OPERAND(lhs, 0);
+if (this.outparams.has(e)) {
+if (expr_literal_int(rhs) == 0) {
+state.assignValue(e, av.WROTE_NULL, isn);
+} else if (DECL_P(rhs)) {
+state.update(function(ss) {
+let [s1, s2] = [ss.copy(), ss]; // s1 NULL, s2 non-NULL
+s1.assignValue(e, av.WROTE_NULL, isn);
+s1.assignValue(rhs, av.ZERO, isn);
+s2.assignValue(e, av.WRITTEN, isn);
+s2.assignValue(rhs, av.NONZERO, isn);
+return [s1,s2];
+});
+} else {
+state.assignValue(e, av.WRITTEN, isn);
+}
+} else {
+// unsound -- could be writing to anything through this ptr
+}
+break;
+case COMPONENT_REF: // unsound
+case ARRAY_REF: // unsound
+case EXC_PTR_EXPR:
+case FILTER_EXPR:
+break;
+default:
+print(TREE_CODE(lhs));
+throw new Error("ni");
+}
+}
+// Handle an assignment x := test(foo) where test is a simple predicate
+OutparamCheck.prototype.processTest = function(lhs, call, val, blame, state) {
+let arg = gimple_call_arg(call, 0);
+if (DECL_P(arg)) {
+this.zeroNonzero.predicate(state, lhs, val, arg, blame);
+} else {
+state.assignValue(lhs, ESP.TOP, blame);
+}
+};
+// The big one: outparam semantics of function calls.
+OutparamCheck.prototype.processCall = function(call, blame, state, dest) {
+if (!dest)
+dest = gimple_call_lhs(call);
+let args = gimple_call_args(call);
+let callable = callable_arg_function_decl(gimple_call_fn(call));
+let psem = this.func_param_semantics(callable);
+let name = function_decl_name(callable);
+if (name == 'NS_FAILED') {
+this.processTest(dest, call, av.NONZERO, call, state);
+return;
+} else if (name == 'NS_SUCCEEDED') {
+this.processTest(dest, call, av.ZERO, call, state);
+return;
+} else if (name == '__builtin_expect') {
+// Same as an assign from arg 0 to lhs
+state.assign(dest, args[0], call);
+return;
+}
+if (TRACE_CALL_SEM) {
+print("param semantics:" + psem);
+}
+if (args.length != psem.length) {
+let ct = TREE_TYPE(callable);
+if (TREE_CODE(ct) == POINTER_TYPE) ct = TREE_TYPE(ct);
+if (args.length < psem.length || !stdarg_p(ct)) {
+// TODO Can __builtin_memcpy write to an outparam? Probably not.
+if (name != 'operator new' && name != 'operator delete' &&
+name != 'operator new []' && name != 'operator delete []' &&
+name.substr(0, 5) != '__cxa' &&
+name.substr(0, 9) != '__builtin') {
+throw Error("bad len for '" + name + "': " + args.length + ' args, ' +
+psem.length + ' params');
+}
+}
+}
+// Collect variables that are possibly written to on callee success
+let updates = [];
+for (let i = 0; i < psem.length; ++i) {
+let arg = args[i];
+// The arg could be the address of a return-value variable.
+// This means it's really the nsresult code for the call,
+// so we treat it the same as the target of an rv assignment.
+if (TREE_CODE(arg) == ADDR_EXPR) {
+let v = arg.operands()[0];
+if (DECL_P(v) && this.retvar_set.has(v)) {
+dest = v;
+}
+}
+// The arg could be a copy of an outparam. We'll unwrap to the
+// outparam if it is. The following is cheating a bit because
+// we munge states together, but it should be OK in practice.
+arg = unwrap_outparam(arg, state);
+let sem = psem[i];
+if (sem == ps.CONST) continue;
+// At this point, we know the call can write thru this param.
+// Invalidate any vars whose addresses are passed here. This
+// is distinct from the rv handling above.
+if (TREE_CODE(arg) == ADDR_EXPR) {
+let v = arg.operands()[0];
+if (DECL_P(v)) {
+state.remove(v);
+}
+}
+if (!DECL_P(arg) || !this.outparams.has(arg)) continue;
+// At this point, we may be writing to an outparam
+updates.push([arg, sem]);
+}
+if (updates.length) {
+if (dest != undefined && DECL_P(dest)) {
+// Update & stored rv. Do updates predicated on success.
+let [ succ_ret, fail_ret ] = ret_coding(callable);
+state.update(function(ss) {
+let [s1, s2] = [ss.copy(), ss]; // s1 success, s2 fail
+for each (let [vbl, sem] in updates) {
+s1.assignValue(vbl, sem.val, blame);
+s1.assignValue(dest, succ_ret, blame);
+}
+s2.assignValue(dest, fail_ret, blame);
+return [s1,s2];
+});
+} else {
+// Discarded rv. Per spec in the bug, we assume that either success
+// or failure is possible (if not, callee should return void).
+// Exceptions: Methods that return void and string mutators are
+//     considered no-fail.
+state.update(function(ss) {
+for each (let [vbl, sem] in updates) {
+if (sem == ps.OUTNOFAIL || sem == ps.OUTNOFAILNOCHECK) {
+ss.assignValue(vbl, av.WRITTEN, blame);
+return [ss];
+} else {
+let [s1, s2] = [ss.copy(), ss]; // s1 success, s2 fail
+for each (let [vbl, sem] in updates) {
+s1.assignValue(vbl, sem.val, blame);
+}
+return [s1,s2];
+}
+}
+});
+}
+} else {
+// no updates, just kill any destination for the rv
+if (dest != undefined && DECL_P(dest)) {
+state.remove(dest, blame);
+}
+}
+};
+/** Return the return value coding of the given function. This is a pair
+*  [ succ, fail ] giving the abstract values of the return value under
+*  success and failure conditions. */
+function ret_coding(callable) {
+let type = TREE_TYPE(callable);
+if (TREE_CODE(type) == POINTER_TYPE) type = TREE_TYPE(type);
+let rtname = TYPE_NAME(TREE_TYPE(type));
+if (rtname && IDENTIFIER_POINTER(DECL_NAME(rtname)) == 'PRBool') {
+return [ av.NONZERO, av.ZERO ];
+} else {
+return [ av.ZERO, av.NONZERO ];
+}
+}
+function unwrap_outparam(arg, state) {
+if (!DECL_P(arg) || state.factory.outparams.has(arg)) return arg;
+let outparam;
+for (let ss in state.substates.getValues()) {
+let val = ss.get(arg);
+if (val != undefined && val.hasOwnProperty('outparam')) {
+outparam = val.outparam;
+}
+}
+if (outparam) return outparam;
+return arg;
+}
+// Check for errors. Must .run() analysis before calling this.
+OutparamCheck.prototype.check = function(isvoid, fndecl) {
+let state = this.cfg.x_exit_block_ptr.stateOut;
+for (let substate in state.substates.getValues()) {
+this.checkSubstate(isvoid, fndecl, substate);
+}
+}
+OutparamCheck.prototype.checkSubstate = function(isvoid, fndecl, ss) {
+if (isvoid) {
+this.checkSubstateSuccess(ss);
+} else {
+let [succ, fail] = ret_coding(fndecl);
+let rv = ss.get(this.retvar);
+// We want to check if the abstract value of the rv is entirely
+// contained in the success or failure condition.
+if (av.meet(rv, succ) == rv) {
+this.checkSubstateSuccess(ss);
+} else if (av.meet(rv, fail) == rv) {
+this.checkSubstateFailure(ss);
+} else {
+// This condition indicates a bug in outparams.js. We'll just
+// warn so we don't break static analysis builds.
+warning("Outparams checker cannot determine rv success/failure",
+location_of(fndecl));
+this.checkSubstateSuccess(ss);
+this.checkSubstateFailure(ss);
+}
+}
+}
+/* @return     The return statement in the function
+*             that writes the return value in the given substate.
+*             If the function returns void, then the substate doesn't
+*             matter and we just look for the return. */
+OutparamCheck.prototype.findReturnStmt = function(ss) {
+if (this.retvar != undefined)
+return ss.getBlame(this.retvar);
+if (this.cfg._cached_return)
+return this.cfg._cached_return;
+for (let bb in cfg_bb_iterator(this.cfg)) {
+for (let isn in bb_isn_iterator(bb)) {
+if (isn.tree_code() == GIMPLE_RETURN) {
+return this.cfg._cached_return = isn;
+}
+}
+}
+return undefined;
+}
+OutparamCheck.prototype.checkSubstateSuccess = function(ss) {
+for (let i = 0; i < this.psem_list.length; ++i) {
+let [v, psem] = [ this.outparam_list[i], this.psem_list[i] ];
+if (psem == ps.INOUT) continue;
+let val = ss.get(v);
+if (val == av.NOT_WRITTEN) {
+this.logResult('succ', 'not_written', 'error');
+this.warn([this.findReturnStmt(ss), "outparam '" + expr_display(v) + "' not written on NS_SUCCEEDED(return value)"],
+[v, "outparam declared here"]);
+} else if (val == av.MAYBE_WRITTEN) {
+this.logResult('succ', 'maybe_written', 'error');
+let blameStmt = ss.getBlame(v);
+let callMsg;
+let callName = "";
+try {
+let call = TREE_CHECK(blameStmt, GIMPLE_CALL, GIMPLE_MODIFY_STMT);
+let callDecl = callable_arg_function_decl(gimple_call_fn(call));
+callMsg = [callDecl, "declared here"];
+callName = " '" + decl_name(callDecl) + "'";
+}
+catch (e if e.TreeCheckError) { }
+this.warn([this.findReturnStmt(ss), "outparam '" + expr_display(v) + "' not written on NS_SUCCEEDED(return value)"],
+[v, "outparam declared here"],
+[blameStmt, "possibly written by unannotated function call" + callName],
+callMsg);
+} else {
+this.logResult('succ', '', 'ok');
+}
+}
+}
+OutparamCheck.prototype.checkSubstateFailure = function(ss) {
+for (let i = 0; i < this.psem_list.length; ++i) {
+let [v, ps] = [ this.outparam_list[i], this.psem_list[i] ];
+let val = ss.get(v);
+if (val == av.WRITTEN) {
+this.logResult('fail', 'written', 'error');
+if (WARN_ON_SET_FAILURE) {
+this.warn([this.findReturnStmt(ss), "outparam '" + expr_display(v) + "' written on NS_FAILED(return value)"],
+[v, "outparam declared here"],
+[ss.getBlame(v), "written here"]);
+}
+} else if (val == av.WROTE_NULL) {
+this.logResult('fail', 'wrote_null', 'warning');
+if (WARN_ON_SET_NULL) {
+this.warn([this.findReturnStmt(ss), "NULL written to outparam '" + expr_display(v) + "' on NS_FAILED(return value)"],
+[v, "outparam declared here"],
+[ss.getBlame(v), "written here"]);
+}
+} else {
+this.logResult('fail', '', 'ok');
+}
+}
+}
+/**
+* Generate a warning from one or more tuples [treeforloc, message]
+*/
+OutparamCheck.prototype.warn = function(arg0) {
+let loc = safe_location_of(arg0[0]);
+let msg = arg0[1];
+for (let i = 1; i < arguments.length; ++i) {
+if (arguments[i] === undefined) continue;
+let [atree, amsg] = arguments[i];
+msg += "\n" + loc_string(safe_location_of(atree)) + ":   " + amsg;
+}
+warning(msg, loc);
+}
+OutparamCheck.prototype.logResult = function(rv, msg, kind) {
+if (LOG_RESULTS) {
+let s = [ '"' + x + '"' for each (x in [ loc_string(location_of(this.fndecl)), function_decl_name(this.fndecl), rv, msg, kind ]) ].join(', ');
+print(":LR: (" + s + ")");
+}
+}
+// Parameter Semantics values -- indicates whether a parameter is
+// an outparam.
+//    label    Used for debugging output
+//    val      Abstract value (state) that holds on an argument after
+//             a call
+//    check    True if parameters with this semantics should be
+//             checked by this analysis
+let ps = {
+OUTNOFAIL: { label: 'out-no-fail', val: av.WRITTEN,  check: true },
+// Special value for receiver of strings methods. Callers should
+// consider this to be an outparam (i.e., it modifies the string),
+// but we don't want to check the method itself.
+OUTNOFAILNOCHECK: { label: 'out-no-fail-no-check' },
+OUT:       { label: 'out',         val: av.WRITTEN,  check: true },
+INOUT:     { label: 'inout',       val: av.WRITTEN,  check: true },
+MAYBE:     { label: 'maybe',       val: av.MAYBE_WRITTEN},  // maybe out
+CONST:     { label: 'const' }   // i.e. not out
+};
+// Return the param semantics of a FUNCTION_DECL or VAR_DECL representing
+// a function pointer. The result is a pair [ ann, sems ].
+OutparamCheck.prototype.func_param_semantics = function(callable) {
+let ftype = TREE_TYPE(callable);
+if (TREE_CODE(ftype) == POINTER_TYPE) ftype = TREE_TYPE(ftype);
+// What failure semantics to use for outparams
+let rtype = TREE_TYPE(ftype);
+let nofail = TREE_CODE(rtype) == VOID_TYPE;
+// Whether to guess outparams by type
+let guess = type_string(rtype) == 'nsresult';
+// Set up param lists for analysis
+let params;     // param decls, if available
+let types;      // param types
+let string_mutator = false;
+if (TREE_CODE(callable) == FUNCTION_DECL) {
+params = [ p for (p in function_decl_params(callable)) ];
+types = [ TREE_TYPE(p) for each (p in params) ];
+string_mutator = is_string_mutator(callable);
+} else {
+types = [ p for (p in function_type_args(ftype))
+if (TREE_CODE(p) != VOID_TYPE) ];
+}
+// Analyze params
+let ans = [];
+for (let i = 0; i < types.length; ++i) {
+let sem;
+if (i == 0 && string_mutator) {
+// Special case: string mutator receiver is an no-fail outparams
+//               but not checkable
+sem = ps.OUTNOFAILNOCHECK;
+} else {
+if (params) sem = decode_attr(DECL_ATTRIBUTES(params[i]));
+if (TRACE_CALL_SEM >= 2) print("param " + i + ": annotated " + sem);
+if (sem == undefined) {
+sem = decode_attr(TYPE_ATTRIBUTES(types[i]));
+if (TRACE_CALL_SEM >= 2) print("type " + i + ": annotated " + sem);
+if (sem == undefined) {
+if (guess && type_is_outparam(types[i])) {
+// Params other than last are guessed as MAYBE
+sem = i < types.length - 1 ? ps.MAYBE : ps.OUT;
+} else {
+sem = ps.CONST;
+}
+}
+}
+if (sem == ps.OUT && nofail) sem = ps.OUTNOFAIL;
+}
+if (sem == undefined) throw new Error("assert");
+ans.push(sem);
+}
+return ans;
+}
+/* Decode parameter semantics GCC attributes.
+* @param attrs    GCC attributes of a parameter. E.g., TYPE_ATTRIBUTES
+*                 or DECL_ATTRIBUTES of an item
+* @return         The parameter semantics value defined by the attributes,
+*                 or undefined if no such attributes were present. */
+function decode_attr(attrs) {
+// Note: we're not checking for conflicts, we just take the first
+// one we find.
+for each (let attr in rectify_attributes(attrs)) {
+if (attr.name == 'user') {
+for each (let arg in attr.args) {
+if (arg == 'NS_outparam') {
+return ps.OUT;
+} else if (arg == 'NS_inoutparam') {
+return ps.INOUT;
+} else if (arg == 'NS_inparam') {
+return ps.CONST;
+}
+}
+}
+}
+return undefined;
+}
+/* @return       true if the given type appears to be an outparam
+*               type based on the type alone (i.e., not considering
+*               attributes. */
+function type_is_outparam(type) {
+switch (TREE_CODE(type)) {
+case POINTER_TYPE:
+return pointer_type_is_outparam(TREE_TYPE(type));
+case REFERENCE_TYPE:
+let rt = TREE_TYPE(type);
+return !TYPE_READONLY(rt) && is_string_type(rt);
+default:
+// Note: This is unsound for UNION_TYPE, because the union could
+//       contain a pointer.
+return false;
+}
+}
+/* Helper for type_is_outparam.
+* @return      true if 'pt *' looks like an outparam type. */
+function pointer_type_is_outparam(pt) {
+if (TYPE_READONLY(pt)) return false;
+switch (TREE_CODE(pt)) {
+case POINTER_TYPE:
+case ARRAY_TYPE: {
+// Look for void **, nsIFoo **, char **, PRUnichar **
+let ppt = TREE_TYPE(pt);
+let tname = TYPE_NAME(ppt);
+if (tname == undefined) return false;
+let name = decl_name_string(tname);
+return name == 'void' || name == 'char' || name == 'PRUnichar' ||
+name.substr(0, 3) == 'nsI';
+}
+case INTEGER_TYPE: {
+// char * and PRUnichar * are probably strings, otherwise guess
+// it is an integer outparam.
+let name = decl_name_string(TYPE_NAME(pt));
+return name != 'char' && name != 'PRUnichar';
+}
+case ENUMERAL_TYPE:
+case REAL_TYPE:
+case UNION_TYPE:
+case BOOLEAN_TYPE:
+return true;
+case RECORD_TYPE:
+// TODO: should we consider field writes?
+return false;
+case FUNCTION_TYPE:
+case VOID_TYPE:
+return false;
+default:
+throw new Error("can't guess if a pointer to this type is an outparam: " +
+TREE_CODE(pt) + ': ' + type_string(pt));
+}
+}
+// Map type name to boolean as to whether it is a string.
+let cached_string_types = MapFactory.create_map(
+function (x, y) x == y,
+function (x) x,
+function (t) t,
+function (t) t);
+// Base string types. Others will be found by searching the inheritance
+// graph.
+cached_string_types.put('nsAString', true);
+cached_string_types.put('nsACString', true);
+cached_string_types.put('nsAString_internal', true);
+cached_string_types.put('nsACString_internal', true);
+// Return true if the given type represents a Mozilla string type.
+// The binfo arg is the binfo to use for further iteration. This is
+// for internal use only, users of this function should pass only
+// one arg.
+function is_string_type(type, binfo) {
+if (TREE_CODE(type) != RECORD_TYPE) return false;
+//print(">>>IST " + type_string(type));
+let name = decl_name_string(TYPE_NAME(type));
+let ans = cached_string_types.get(name);
+if (ans != undefined) return ans;
+ans = false;
+binfo = binfo != undefined ? binfo : TYPE_BINFO(type);
+if (binfo != undefined) {
+for each (let base in VEC_iterate(BINFO_BASE_BINFOS(binfo))) {
+let parent_ans = is_string_type(BINFO_TYPE(base), base);
+if (parent_ans) {
+ans = true;
+break;
+}
+}
+}
+cached_string_types.put(name, ans);
+//print("<<<IST " + type_string(type) + ' ' + ans);
+return ans;
+}
+function is_string_ptr_type(type) {
+return TREE_CODE(type) == POINTER_TYPE && is_string_type(TREE_TYPE(type));
+}
+// Return true if the given function is a mutator method of a Mozilla
+// string type.
+function is_string_mutator(fndecl) {
+let first_param = function() {
+for (let p in function_decl_params(fndecl)) {
+return p;
+}
+return undefined;
+}();
+return first_param != undefined &&
+decl_name_string(first_param) == 'this' &&
+is_string_ptr_type(TREE_TYPE(first_param)) &&
+!TYPE_READONLY(TREE_TYPE(TREE_TYPE(first_param)));
+}