C++ and Java CNI: Check Java references

Mon Apr 23 12:15:00 GMT 2001

Shoudn't that be a #pragma put on the top of the CNI file?
Cedric
Andrew Haley wrote:
> The semantics of Java require dereferencing a null pointer to an
> object to throw a NullPointerException. We already generate code to
> do this in the Java compiler; this patch is for CNI code that is
> written in C++.
>> An alternative way to do this is to trap SEGV and throw an exception
> from a signal handler but not every processor/OS combination allows
> this, and we haven't ported code to do this to many systems.
>> This patch only throws a NullPointerException from references to Java
> objects, not for arbitrary pointer dereferencing. People writing CNI
> code had better check non-Java pointers themselves.
>> I'm not absolutely sure where this option should be documented.
> Should it be documented anywhere other than in the gcj docs?
>> There is an associated patch for libgcj that is required in order to
> use this option.
>> Andrew.
>> 2001年04月23日 Andrew Haley <aph@cambridge.redhat.com>
>> * lang-options.h: Document "-fcheck-java-references".
> * decl2.c (flag_check_java_references): New flag.
> * cp-tree.h (flag_check_java_references): New flag.
> (lang_f_options): Set lang_check_java_references.
> (check_java_reference): New function.
> * call.c (check_java_reference): New function.
> * typeck.c (build_indirect_ref): Call check_java_reference on Java
> objects.
>> Index: call.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cp/call.c,v
> retrieving revision 1.265
> diff -p -2 -c -r1.265 call.c
> *** call.c 2001年03月23日 01:49:10 1.265
> --- call.c 2001年04月23日 17:18:18
> *************** initialize_reference (type, expr)
> *** 5534,5535 ****
> --- 5534,5591 ----
> return convert_like (conv, expr);
> }
> +
> + static tree java_nullpointer_exception;
> +
> + tree
> + check_java_reference (exp)
> + tree exp;
> + {
> + tree e = exp;
> +
> + if (!flag_check_java_references)
> + return exp;
> +
> + /* Strip off all pointer conversions and if the thing at the root is
> + an integer we won't bother to check it. The main reason for this
> + is that offsetof is often defined as
> +
> + ((size_t)&((type *)0)->memb)
> +
> + which implicitly dereferences a null pointer. Let's not check that. */
> +
> + while (TREE_CODE (e) == NOP_EXPR
> + && TREE_CODE (TREE_TYPE (e)) == POINTER_TYPE)
> + (e) = TREE_OPERAND (e, 0);
> +
> + if (TREE_CODE (e) == INTEGER_CST)
> + return exp;
> +
> + if (java_nullpointer_exception == NULL_TREE)
> + {
> + tree endlink = build_void_list_node ();
> + java_nullpointer_exception
> + = builtin_function ("_Jv_ThrowNullPointerException",
> + build_function_type (void_type_node, endlink),
> + 0, NOT_BUILT_IN, NULL_PTR);
> + TREE_THIS_VOLATILE (java_nullpointer_exception) = 1;
> + TREE_SIDE_EFFECTS (java_nullpointer_exception) = 1;
> + java_nullpointer_exception
> + = build1 (ADDR_EXPR,
> + build_pointer_type
> + (TREE_TYPE (java_nullpointer_exception)),
> + java_nullpointer_exception);
> + ggc_add_tree_root (&java_nullpointer_exception, 1);
> + }
> +
> + exp = stabilize_reference (exp);
> + {
> + tree cond = build (NE_EXPR, boolean_type_node, exp, integer_zero_node);
> + tree bad =
> + build (CALL_EXPR, void_type_node,
> + java_nullpointer_exception,
> + NULL_TREE, NULL_TREE);
> + exp = build (COND_EXPR, TREE_TYPE (exp), cond, exp, bad);
> + }
> +
> + return exp;
> + }
> Index: cp-tree.h
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cp/cp-tree.h,v
> retrieving revision 1.590
> diff -p -2 -c -r1.590 cp-tree.h
> *** cp-tree.h 2001年03月26日 08:37:24 1.590
> --- cp-tree.h 2001年04月23日 17:18:28
> *************** extern int flag_access_control;
> *** 1146,1149 ****
> --- 1146,1153 ----
> extern int flag_check_new;
>> + /* Java objects: when non zero, generate checks for references to
> + NULL. */
> + extern int flag_check_java_references;
> +
> /* Nonnull if we want to dump class heirarchies. */
>> *************** extern tree initialize_reference
> *** 3699,3702 ****
> --- 3703,3707 ----
> extern tree strip_top_quals PARAMS ((tree));
> extern tree perform_implicit_conversion PARAMS ((tree, tree));
> + extern tree check_java_reference PARAMS ((tree));
>> /* in class.c */
> Index: decl2.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cp/decl2.c,v
> retrieving revision 1.448
> diff -p -2 -c -r1.448 decl2.c
> *** decl2.c 2001年03月22日 00:55:11 1.448
> --- decl2.c 2001年04月23日 17:18:38
> *************** int flag_enforce_eh_specs = 1;
> *** 448,451 ****
> --- 448,455 ----
> c_language_kind c_language = clk_cplusplus;
>> + /* Java objects: when non zero, generate checks for references to
> + NULL. */
> + int flag_check_java_references = 0;
> +
> /* Table of language-dependent -f options.
> STRING is the option name. VARIABLE is the address of the variable.
> *************** lang_f_options[] =
> *** 471,474 ****
> --- 475,479 ----
> {"access-control", &flag_access_control, 1},
> {"check-new", &flag_check_new, 1},
> + {"check-java-references", &flag_check_java_references, 1},
> {"conserve-space", &flag_conserve_space, 1},
> {"const-strings", &flag_const_strings, 1},
> Index: lang-options.h
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cp/lang-options.h,v
> retrieving revision 1.37
> diff -p -2 -c -r1.37 lang-options.h
> *** lang-options.h 2001年01月05日 19:12:19 1.37
> --- lang-options.h 2001年04月23日 17:18:40
> *************** DEFINE_LANG_NAME ("C++")
> *** 112,115 ****
> --- 112,116 ----
> { "-fxref", "Emit cross referencing information" },
> { "-fno-xref", "" },
> + { "-fcheck-java-references", "Generate null pointer checks for Java objects" },
>> { "-Wreturn-type", "Warn about inconsistent return types" },
> Index: typeck.c
> ===================================================================
> RCS file: /cvs/gcc/gcc/gcc/cp/typeck.c,v
> retrieving revision 1.342
> diff -p -2 -c -r1.342 typeck.c
> *** typeck.c 2001年03月06日 20:45:05 1.342
> --- typeck.c 2001年04月23日 17:18:45
> *************** build_indirect_ref (ptr, errorstring)
> *** 2380,2384 ****
> else
> {
> ! tree ref = build1 (INDIRECT_REF, t, pointer);
>> /* We *must* set TREE_READONLY when dereferencing a pointer to const,
> --- 2380,2388 ----
> else
> {
> ! tree ref
> ! = build1 (INDIRECT_REF, t,
> ! TYPE_FOR_JAVA (t) && AGGREGATE_TYPE_P (t)
> ! ? check_java_reference (pointer)
> ! : pointer);
>> /* We *must* set TREE_READONLY when dereferencing a pointer to const,