From 4dc7ce6fb3917958d1a6036d8acf2953b9c1b868 Mon Sep 17 00:00:00 2001 From: Martin Sebor Date: Fri, 1 Oct 2021 11:50:25 -0600 Subject: Enhance -Waddress to detect more suspicious expressions [PR102103]. Resolves: PR c/102103 - missing warning comparing array address to null gcc/ChangeLog: PR c/102103 * doc/invoke.texi (-Waddress): Update. * gengtype.c (write_types): Avoid -Waddress. * poly-int.h (POLY_SET_COEFF): Avoid using null. gcc/c-family/ChangeLog: PR c/102103 * c-common.c (decl_with_nonnull_addr_p): Handle members. Check and perform warning suppression. (c_common_truthvalue_conversion): Enhance warning suppression. gcc/c/ChangeLog: PR c/102103 * c-typeck.c (maybe_warn_for_null_address): New function. (build_binary_op): Call it. gcc/cp/ChangeLog: PR c/102103 * typeck.c (warn_for_null_address): Enhance. (cp_build_binary_op): Call it also for member pointers. gcc/fortran/ChangeLog: PR c/102103 * array.c: Remove an unnecessary test. * trans-array.c: Same. gcc/testsuite/ChangeLog: PR c/102103 * g++.dg/cpp0x/constexpr-array-ptr10.C: Suppress a valid warning. * g++.dg/warn/Wreturn-local-addr-6.C: Correct a cast. * gcc.dg/Waddress.c: Expect a warning. * c-c++-common/Waddress-3.c: New test. * c-c++-common/Waddress-4.c: New test. * g++.dg/warn/Waddress-5.C: New test. * g++.dg/warn/Waddress-6.C: New test. * g++.dg/warn/pr101219.C: Expect a warning. * gcc.dg/Waddress-3.c: New test. --- gcc/c/c-typeck.c | 140 +++++++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 106 insertions(+), 34 deletions(-) (limited to 'gcc/c') diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c index c74f876..33963d7 100644 --- a/gcc/c/c-typeck.c +++ b/gcc/c/c-typeck.c @@ -11554,6 +11554,110 @@ build_vec_cmp (tree_code code, tree type, return build3 (VEC_COND_EXPR, type, cmp, minus_one_vec, zero_vec); } +/* Possibly warn about an address of OP never being NULL in a comparison + operation CODE involving null. */ + +static void +maybe_warn_for_null_address (location_t loc, tree op, tree_code code) +{ + if (!warn_address || warning_suppressed_p (op, OPT_Waddress)) + return; + + if (TREE_CODE (op) == NOP_EXPR) + { + /* Allow casts to intptr_t to suppress the warning. */ + tree type = TREE_TYPE (op); + if (TREE_CODE (type) == INTEGER_TYPE) + return; + op = TREE_OPERAND (op, 0); + } + + if (TREE_CODE (op) == POINTER_PLUS_EXPR) + { + /* Allow a cast to void* to suppress the warning. */ + tree type = TREE_TYPE (TREE_TYPE (op)); + if (VOID_TYPE_P (type)) + return; + + /* Adding any value to a null pointer, including zero, is undefined + in C. This includes the expression &p[0] where p is the null + pointer, although &p[0] will have been folded to p by this point + and so not diagnosed. */ + if (code == EQ_EXPR) + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the pointer operand in %qE must not be NULL", + op); + else + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the pointer operand in %qE must not be NULL", + op); + + return; + } + + if (TREE_CODE (op) != ADDR_EXPR) + return; + + op = TREE_OPERAND (op, 0); + + if (TREE_CODE (op) == IMAGPART_EXPR + || TREE_CODE (op) == REALPART_EXPR) + { + /* The address of either complex part may not be null. */ + if (code == EQ_EXPR) + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the address of %qE will never be NULL", + op); + else + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the address of %qE will never be NULL", + op); + return; + } + + /* Set to true in the loop below if OP dereferences is operand. + In such a case the ultimate target need not be a decl for + the null [in]equality test to be constant. */ + bool deref = false; + + /* Get the outermost array or object, or member. */ + while (handled_component_p (op)) + { + if (TREE_CODE (op) == COMPONENT_REF) + { + /* Get the member (its address is never null). */ + op = TREE_OPERAND (op, 1); + break; + } + + /* Get the outer array/object to refer to in the warning. */ + op = TREE_OPERAND (op, 0); + deref = true; + } + + if ((!deref && !decl_with_nonnull_addr_p (op)) + || from_macro_expansion_at (loc)) + return; + + if (code == EQ_EXPR) + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the address of %qE will never be NULL", + op); + else + warning_at (loc, OPT_Waddress, + "the comparison will always evaluate as % " + "for the address of %qE will never be NULL", + op); + + if (DECL_P (op)) + inform (DECL_SOURCE_LOCATION (op), "%qD declared here", op); +} + /* Build a binary-operation expression without default conversions. CODE is the kind of expression to build. LOCATION is the operator's location. @@ -12189,44 +12293,12 @@ build_binary_op (location_t location, enum tree_code code, short_compare = 1; else if (code0 == POINTER_TYPE && null_pointer_constant_p (orig_op1)) { - if (TREE_CODE (op0) == ADDR_EXPR - && decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)) - && !from_macro_expansion_at (location)) - { - if (code == EQ_EXPR) - warning_at (location, - OPT_Waddress, - "the comparison will always evaluate as % " - "for the address of %qD will never be NULL", - TREE_OPERAND (op0, 0)); - else - warning_at (location, - OPT_Waddress, - "the comparison will always evaluate as % " - "for the address of %qD will never be NULL", - TREE_OPERAND (op0, 0)); - } + maybe_warn_for_null_address (location, op0, code); result_type = type0; } else if (code1 == POINTER_TYPE && null_pointer_constant_p (orig_op0)) { - if (TREE_CODE (op1) == ADDR_EXPR - && decl_with_nonnull_addr_p (TREE_OPERAND (op1, 0)) - && !from_macro_expansion_at (location)) - { - if (code == EQ_EXPR) - warning_at (location, - OPT_Waddress, - "the comparison will always evaluate as % " - "for the address of %qD will never be NULL", - TREE_OPERAND (op1, 0)); - else - warning_at (location, - OPT_Waddress, - "the comparison will always evaluate as % " - "for the address of %qD will never be NULL", - TREE_OPERAND (op1, 0)); - } + maybe_warn_for_null_address (location, op1, code); result_type = type1; } else if (code0 == POINTER_TYPE && code1 == POINTER_TYPE) -- cgit v1.1