Warn when returning the address of a temporary (middle-end) v2

Message ID	alpine.DEB.2.02.1406221930380.20514@stedding.saclay.inria.fr
State	New
Headers	show Return-Path: <gcc-patches-return-370772-incoming=patchwork.ozlabs.org@gcc.gnu.org> DomainKey-Signature: a=rsa-sha1; c=nofws; d=gcc.gnu.org; h=list-id :list-unsubscribe:list-archive:list-post:list-help:sender:date :from:to:subject:message-id:mime-version:content-type; q=dns; s= default; b=OT5fvUnrFu5sATYEtp9FWi48y3zkG8DJDDN0B2CrSHxUqytf0tJMK G0mnYlfPgXKrct5L93RQCYSt2CpILpmxJdmdziYcr9ffCs/XVvXJPPKJ9/qJjB6Y T6uAI3Pg8gv6msJFWdPfjbqDTzBwCyimRFQR8NtOu7RJeOoU+35Krc= Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk Sender: gcc-patches-owner@gcc.gnu.org Date: Sun, 22 Jun 2014 20:20:41 +0200 (CEST) From: Marc Glisse <marc.glisse@inria.fr> To: gcc-patches@gcc.gnu.org Subject: Warn when returning the address of a temporary (middle-end) v2 Message-ID: <alpine.DEB.2.02.1406221930380.20514@stedding.saclay.inria.fr> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="8323329-701475119-1403461241=:20514"

Index: gcc/c/c-typeck.c =================================================================== --- gcc/c/c-typeck.c (revision 211874) +++ gcc/c/c-typeck.c (working copy) @@ -9315,22 +9315,26 @@ c_finish_return (location_t loc, tree re if (DECL_P (inner) && !DECL_EXTERNAL (inner) && !TREE_STATIC (inner) && DECL_CONTEXT (inner) == current_function_decl) { if (TREE_CODE (inner) == LABEL_DECL) warning_at (loc, OPT_Wreturn_local_addr, "function returns address of label"); else - warning_at (loc, OPT_Wreturn_local_addr, - "function returns address of local variable"); + { + warning_at (loc, OPT_Wreturn_local_addr, + "function returns address of local variable"); + tree zero = build_zero_cst (TREE_TYPE (res)); + t = build_compound_expr (loc, t, zero); + } } break; default: break; } break; } Index: gcc/c-family/c.opt =================================================================== --- gcc/c-family/c.opt (revision 211874) +++ gcc/c-family/c.opt (working copy) @@ -682,24 +682,20 @@ ObjC ObjC++ Var(warn_protocol) Init(1) W Warn if inherited methods are unimplemented Wredundant-decls C ObjC C++ ObjC++ Var(warn_redundant_decls) Warning Warn about multiple declarations of the same object Wreorder C++ ObjC++ Var(warn_reorder) Warning LangEnabledBy(C++ ObjC++,Wall) Warn when the compiler reorders code -Wreturn-local-addr -C ObjC C++ ObjC++ Var(warn_return_local_addr) Init(1) Warning -Warn about returning a pointer/reference to a local or temporary variable. - Wreturn-type C ObjC C++ ObjC++ Var(warn_return_type) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall) Warn whenever a function's return type defaults to \"int\" (C), or about inconsistent return types (C++) Wselector ObjC ObjC++ Var(warn_selector) Warning Warn if a selector has multiple methods Wshadow-ivar ObjC ObjC++ Var(warn_shadow_ivar) EnabledBy(Wshadow) Init(1) Warning Index: gcc/common.opt =================================================================== --- gcc/common.opt (revision 211874) +++ gcc/common.opt (working copy) @@ -596,20 +596,24 @@ Common Var(warn_packed) Warning Warn when the packed attribute has no effect on struct layout Wpadded Common Var(warn_padded) Warning Warn when padding is required to align structure members Wpedantic Common Var(pedantic) Warning Issue warnings needed for strict compliance to the standard +Wreturn-local-addr +Common Var(warn_return_local_addr) Init(1) Warning +Warn about returning a pointer/reference to a local or temporary variable. + Wshadow Common Var(warn_shadow) Warning Warn when one local variable shadows another Wstack-protector Common Var(warn_stack_protect) Warning Warn when not issuing stack smashing protection for some reason Wstack-usage= Common Joined RejectNegative UInteger Var(warn_stack_usage) Init(-1) Warning Index: gcc/cp/typeck.c =================================================================== --- gcc/cp/typeck.c (revision 211874) +++ gcc/cp/typeck.c (working copy) @@ -49,21 +49,21 @@ static tree convert_for_assignment (tree static tree cp_pointer_int_sum (enum tree_code, tree, tree, tsubst_flags_t); static tree rationalize_conditional_expr (enum tree_code, tree, tsubst_flags_t); static int comp_ptr_ttypes_real (tree, tree, int); static bool comp_except_types (tree, tree, bool); static bool comp_array_types (const_tree, const_tree, bool); static tree pointer_diff (tree, tree, tree, tsubst_flags_t); static tree get_delta_difference (tree, tree, bool, bool, tsubst_flags_t); static void casts_away_constness_r (tree *, tree *, tsubst_flags_t); static bool casts_away_constness (tree, tree, tsubst_flags_t); -static void maybe_warn_about_returning_address_of_local (tree); +static bool maybe_warn_about_returning_address_of_local (tree); static tree lookup_destructor (tree, tree, tree, tsubst_flags_t); static void warn_args_num (location_t, tree, bool); static int convert_arguments (tree, vec<tree, va_gc> **, tree, int, tsubst_flags_t); /* Do `exp = require_complete_type (exp);' to make sure exp does not have an incomplete type. (That includes void types.) Returns error_mark_node if the VALUE does not have complete type when this function returns. */ @@ -8278,82 +8278,84 @@ convert_for_initialization (tree exp, tr return rhs; if (MAYBE_CLASS_TYPE_P (type)) return perform_implicit_conversion_flags (type, rhs, complain, flags); return convert_for_assignment (type, rhs, errtype, fndecl, parmnum, complain, flags); } /* If RETVAL is the address of, or a reference to, a local variable or - temporary give an appropriate warning. */ + temporary give an appropriate warning and return true. */ -static void +static bool maybe_warn_about_returning_address_of_local (tree retval) { tree valtype = TREE_TYPE (DECL_RESULT (current_function_decl)); tree whats_returned = retval; for (;;) { if (TREE_CODE (whats_returned) == COMPOUND_EXPR) whats_returned = TREE_OPERAND (whats_returned, 1); else if (CONVERT_EXPR_P (whats_returned) || TREE_CODE (whats_returned) == NON_LVALUE_EXPR) whats_returned = TREE_OPERAND (whats_returned, 0); else break; } if (TREE_CODE (whats_returned) != ADDR_EXPR) - return; + return false; whats_returned = TREE_OPERAND (whats_returned, 0); while (TREE_CODE (whats_returned) == COMPONENT_REF || TREE_CODE (whats_returned) == ARRAY_REF) whats_returned = TREE_OPERAND (whats_returned, 0); if (TREE_CODE (valtype) == REFERENCE_TYPE) { if (TREE_CODE (whats_returned) == AGGR_INIT_EXPR || TREE_CODE (whats_returned) == TARGET_EXPR) { warning (OPT_Wreturn_local_addr, "returning reference to temporary"); - return; + return true; } if (VAR_P (whats_returned) && DECL_NAME (whats_returned) && TEMP_NAME_P (DECL_NAME (whats_returned))) { warning (OPT_Wreturn_local_addr, "reference to non-lvalue returned"); - return; + return true; } } if (DECL_P (whats_returned) && DECL_NAME (whats_returned) && DECL_FUNCTION_SCOPE_P (whats_returned) && !is_capture_proxy (whats_returned) && !(TREE_STATIC (whats_returned) || TREE_PUBLIC (whats_returned))) { if (TREE_CODE (valtype) == REFERENCE_TYPE) warning (OPT_Wreturn_local_addr, "reference to local variable %q+D returned", whats_returned); else if (TREE_CODE (whats_returned) == LABEL_DECL) warning (OPT_Wreturn_local_addr, "address of label %q+D returned", whats_returned); else warning (OPT_Wreturn_local_addr, "address of local variable %q+D " "returned", whats_returned); - return; + return true; } + + return false; } /* Check that returning RETVAL from the current function is valid. Return an expression explicitly showing all conversions required to change RETVAL into the function return type, and to assign it to the DECL_RESULT for the function. Set *NO_WARNING to true if code reaches end of non-void function warning shouldn't be issued on this RETURN_EXPR. */ tree @@ -8634,22 +8636,23 @@ check_return_expr (tree retval, bool *no /* If the conversion failed, treat this just like `return;'. */ if (retval == error_mark_node) return retval; /* We can't initialize a register from a AGGR_INIT_EXPR. */ else if (! cfun->returns_struct && TREE_CODE (retval) == TARGET_EXPR && TREE_CODE (TREE_OPERAND (retval, 1)) == AGGR_INIT_EXPR) retval = build2 (COMPOUND_EXPR, TREE_TYPE (retval), retval, TREE_OPERAND (retval, 0)); - else - maybe_warn_about_returning_address_of_local (retval); + else if (maybe_warn_about_returning_address_of_local (retval)) + retval = build2 (COMPOUND_EXPR, TREE_TYPE (retval), retval, + build_zero_cst (TREE_TYPE (retval))); } /* Actually copy the value returned into the appropriate location. */ if (retval && retval != result) retval = build2 (INIT_EXPR, TREE_TYPE (result), result, retval); return retval; } Index: gcc/gimple-ssa-isolate-paths.c =================================================================== --- gcc/gimple-ssa-isolate-paths.c (revision 211874) +++ gcc/gimple-ssa-isolate-paths.c (working copy) @@ -35,20 +35,21 @@ along with GCC; see the file COPYING3. #include "tree-ssa.h" #include "stringpool.h" #include "tree-ssanames.h" #include "gimple-ssa.h" #include "tree-ssa-operands.h" #include "tree-phinodes.h" #include "ssa-iterators.h" #include "cfgloop.h" #include "tree-pass.h" #include "tree-cfg.h" +#include "diagnostic-core.h" static bool cfg_altered; /* Callback for walk_stmt_load_store_ops. Return TRUE if OP will dereference the tree stored in DATA, FALSE otherwise. This routine only makes a superficial check for a dereference. Thus, @@ -125,41 +126,44 @@ insert_trap_and_remove_trailing_statemen /* BB when reached via incoming edge E will exhibit undefined behaviour at STMT. Isolate and optimize the path which exhibits undefined behaviour. Isolation is simple. Duplicate BB and redirect E to BB'. Optimization is simple as well. Replace STMT in BB' with an unconditional trap and remove all outgoing edges from BB'. + If RET_ZERO, do not trap, only return NULL. + DUPLICATE is a pre-existing duplicate, use it as BB' if it exists. Return BB'. */ basic_block isolate_path (basic_block bb, basic_block duplicate, - edge e, gimple stmt, tree op) + edge e, gimple stmt, tree op, bool ret_zero) { gimple_stmt_iterator si, si2; edge_iterator ei; edge e2; /* First duplicate BB if we have not done so already and remove all the duplicate's outgoing edges as duplicate is going to unconditionally trap. Removing the outgoing edges is both an optimization and ensures we don't need to do any PHI node updates. */ if (!duplicate) { duplicate = duplicate_block (bb, NULL, NULL); - for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); ) - remove_edge (e2); + if (!ret_zero) + for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); ) + remove_edge (e2); } /* Complete the isolation step by redirecting E to reach DUPLICATE. */ e2 = redirect_edge_and_branch (e, duplicate); if (e2) flush_pending_stmts (e2); /* There may be more than one statement in DUPLICATE which exhibits undefined behaviour. Ultimately we want the first such statement in @@ -190,21 +194,31 @@ isolate_path (basic_block bb, basic_bloc } /* This would be an indicator that we never found STMT in BB, which should never happen. */ gcc_assert (!gsi_end_p (si)); /* If we did not run to the end of DUPLICATE, then SI points to STMT and SI2 points to the duplicate of STMT in DUPLICATE. Insert a trap before SI2 and remove SI2 and all trailing statements. */ if (!gsi_end_p (si2)) - insert_trap_and_remove_trailing_statements (&si2, op); + { + if (ret_zero) + { + gimple ret = gsi_stmt (si2); + tree zero = build_zero_cst (TREE_TYPE (gimple_return_retval (ret))); + gimple_return_set_retval (ret, zero); + update_stmt (ret); + } + else + insert_trap_and_remove_trailing_statements (&si2, op); + } return duplicate; } /* Look for PHI nodes which feed statements in the same block where the value of the PHI node implies the statement is erroneous. For example, a NULL PHI arg value which then feeds a pointer dereference. @@ -248,47 +262,79 @@ find_implicit_erroneous_behaviour (void) arguments are NULL. When we remove an edge, we want to reprocess the current index, hence the ugly way we update I for each iteration. */ basic_block duplicate = NULL; for (unsigned i = 0, next_i = 0; i < gimple_phi_num_args (phi); i = next_i) { tree op = gimple_phi_arg_def (phi, i); + edge e = gimple_phi_arg_edge (phi, i); + imm_use_iterator iter; + gimple use_stmt; next_i = i + 1; + if (TREE_CODE (op) == ADDR_EXPR) + { + tree valbase = get_base_address (TREE_OPERAND (op, 0)); + if (TREE_CODE (valbase) == VAR_DECL + && !is_global_var (valbase)) + { + FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs) + { + if (gimple_code (use_stmt) != GIMPLE_RETURN + || gimple_return_retval (use_stmt) != lhs) + continue; + + if (warning_at (gimple_location (use_stmt), + OPT_Wreturn_local_addr, + "function may return address " + "of local variable")) + inform (DECL_SOURCE_LOCATION(valbase), + "declared here"); + + if (gimple_bb (use_stmt) == bb) + { + duplicate = isolate_path (bb, duplicate, e, + use_stmt, lhs, true); + + /* When we remove an incoming edge, we need to + reprocess the Ith element. */ + next_i = i; + cfg_altered = true; + } + } + } + } + if (!integer_zerop (op)) continue; - edge e = gimple_phi_arg_edge (phi, i); - imm_use_iterator iter; - gimple use_stmt; - /* We've got a NULL PHI argument. Now see if the PHI's result is dereferenced within BB. */ FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs) { /* We only care about uses in BB. Catching cases in in other blocks would require more complex path isolation code. */ if (gimple_bb (use_stmt) != bb) continue; if (infer_nonnull_range (use_stmt, lhs, flag_isolate_erroneous_paths_dereference, flag_isolate_erroneous_paths_attribute)) { - duplicate = isolate_path (bb, duplicate, - e, use_stmt, lhs); + duplicate = isolate_path (bb, duplicate, e, + use_stmt, lhs, false); /* When we remove an incoming edge, we need to reprocess the Ith element. */ next_i = i; cfg_altered = true; } } } } } @@ -340,23 +386,55 @@ find_explicit_erroneous_behaviour (void) for (edge_iterator ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); ) remove_edge (e); /* Ignore any more operands on this statement and continue the statement iterator (which should terminate its loop immediately. */ cfg_altered = true; break; } + + /* Detect returning the address of a local variable. This only + becomes undefined behavior if the result is used, so we do not + insert a trap and only return NULL instead. */ + if (gimple_code (stmt) == GIMPLE_RETURN) + { + tree val = gimple_return_retval (stmt); + if (val && TREE_CODE (val) == ADDR_EXPR) + { + tree valbase = get_base_address (TREE_OPERAND (val, 0)); + if (TREE_CODE (valbase) == VAR_DECL + && !is_global_var (valbase)) + { + const char* msg; + bool always_executed = dominated_by_p + (CDI_POST_DOMINATORS, + single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)), bb); + if (always_executed) + msg = "function returns address of local variable"; + else + msg = "function may return address of local variable"; + + if (warning_at (gimple_location (stmt), + OPT_Wreturn_local_addr, msg)) + inform (DECL_SOURCE_LOCATION(valbase), "declared here"); + tree zero = build_zero_cst (TREE_TYPE (val)); + gimple_return_set_retval (stmt, zero); + update_stmt (stmt); + } + } + } } } } + /* Search the function for statements which, if executed, would cause the program to fault such as a dereference of a NULL pointer. Such a program can't be valid if such a statement was to execute according to ISO standards. We detect explicit NULL pointer dereferences as well as those implied by a PHI argument having a NULL value which unconditionally flows into a dereference in the same block as the PHI. @@ -371,20 +449,21 @@ find_explicit_erroneous_behaviour (void) A warning for both cases may be advisable as well. Other statically detectable violations of the ISO standard could be handled in a similar way, such as out-of-bounds array indexing. */ static unsigned int gimple_ssa_isolate_erroneous_paths (void) { initialize_original_copy_tables (); + calculate_dominance_info (CDI_POST_DOMINATORS); /* Search all the blocks for edges which, if traversed, will result in undefined behaviour. */ cfg_altered = false; /* First handle cases where traversal of a particular edge triggers undefined behaviour. These cases require creating duplicate blocks and thus new SSA_NAMEs. We want that process complete prior to the phase where we start Index: gcc/testsuite/c-c++-common/addrtmp.c =================================================================== --- gcc/testsuite/c-c++-common/addrtmp.c (revision 0) +++ gcc/testsuite/c-c++-common/addrtmp.c (working copy) @@ -0,0 +1,24 @@ +/* { dg-do compile } */ +/* { dg-options "-O2" } */ + +typedef struct A { int a,b; } A; +int*g(int*x){return x;} +int*f1(){ + A x[2]={{1,2},{3,4}}; + return g(&x[1].a); // { dg-warning "returns address of local variable" } +} +int*f2(int n){ + A x[2]={{1,2},{3,4}}; + return n?0:g(&x[1].a); // { dg-warning "may return address of local variable" } +} +A y[2]={{1,2},{3,4}}; +int*h(){ + return g(&y[1].a); +} +int*j(int n){ + A x[2]={{1,2},{3,4}}; + int*p=g(&y[1].a); + if(n==1)p=g(&x[1].a); + if(n==2)p=g(&x[0].b); + return p; // { dg-warning "may return address of local variable" } +} Index: gcc/testsuite/c-c++-common/uninit-G.c =================================================================== --- gcc/testsuite/c-c++-common/uninit-G.c (revision 211874) +++ gcc/testsuite/c-c++-common/uninit-G.c (working copy) @@ -1,9 +1,10 @@ /* Test we do not warn about initializing variable with address of self in the initialization. */ /* { dg-do compile } */ /* { dg-options "-O -Wuninitialized" } */ -void *f() +void g(void*); +void f() { void *i = &i; - return i; + g(i); }

Warn when returning the address of a temporary (middle-end) v2

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