On Wed, 17 Aug 2022, Qing Zhao wrote: > Add the following new option -fstrict-flex-array[=n] and a corresponding > attribute strict_flex_array to GCC: > > '-fstrict-flex-array' > Treat the trailing array of a structure as a flexible array member > in a stricter way. The positive form is equivalent to > '-fstrict-flex-array=3', which is the strictest. A trailing array > is treated as a flexible array member only when it is declared as a > flexible array member per C99 standard onwards. The negative form > is equivalent to '-fstrict-flex-array=0', which is the least > strict. All trailing arrays of structures are treated as flexible > array members. > > '-fstrict-flex-array=LEVEL' > Treat the trailing array of a structure as a flexible array member > in a stricter way. The value of LEVEL controls the level of > strictness. > > The possible values of LEVEL are the same as for the > 'strict_flex_array' attribute (*note Variable Attributes::). > > You can control this behavior for a specific trailing array field > of a structure by using the variable attribute 'strict_flex_array' > attribute (*note Variable Attributes::). > > This option is only valid when flexible array member is supported in the > language. FOR ISO C before C99 and ISO C++, no language support for the > flexible > array member at all, this option will be invalid and a warning will be > issued. > When -std=gnu89 is specified or C++ with GNU extension, only zero-length > array > extension and one-size array are supported, as a result, LEVEL=3 will be > invalid and a warning will be issued. > > 'strict_flex_array (LEVEL)' > The 'strict_flex_array' attribute should be attached to the > trailing array field of a structure. It specifies the level of > strictness of treating the trailing array field of a structure as a > flexible array member. LEVEL must be an integer betwen 0 to 3. > > LEVEL=0 is the least strict level, all trailing arrays of > structures are treated as flexible array members. LEVEL=3 is the > strictest level, only when the trailing array is declared as a > flexible array member per C99 standard onwards ([]), it is treated > as a flexible array member. > > There are two more levels in between 0 and 3, which are provided to > support older codes that use GCC zero-length array extension ([0]) > or one-size array as flexible array member ([1]): When LEVEL is 1, > the trailing array is treated as a flexible array member when it is > declared as either [], [0], or [1]; When LEVEL is 2, the trailing > array is treated as a flexible array member when it is declared as > either [], or [0]. > > This attribute can be used with or without '-fstrict-flex-array'. > When both the attribute and the option present at the same time, > the level of the strictness for the specific trailing array field > is determined by the attribute. > > This attribute is only valid when flexible array member is supported in > the > language. For ISO C before C99 and ISO C++, no language support for the > flexible > array member at all, this attribute will be invalid and a warning is > issued. > When -std=gnu89 is specified or C++ with GNU extension, only zero-length > array > extension and one-size array are supported, as a result, LEVEL=3 will be > invalid and a warning is issued. > > gcc/c-family/ChangeLog: > > * c-attribs.cc (handle_strict_flex_arrays_attribute): New function. > (c_common_attribute_table): New item for strict_flex_array. > * c-opts.cc (c_common_post_options): Handle the combination of > -fstrict-flex-arrays and -std specially. > * c.opt: (fstrict-flex-array): New option. > (fstrict-flex-array=): New option. > > gcc/c/ChangeLog: > > * c-decl.cc (flexible_array_member_type_p): New function. > (one_element_array_type_p): Likewise. > (zero_length_array_type_p): Likewise. > (add_flexible_array_elts_to_size): Call new utility > routine flexible_array_member_type_p. > (is_flexible_array_member_p): New function. > (finish_struct): Set the new DECL_NOT_FLEXARRAY flag. > > gcc/cp/ChangeLog: > > * module.cc (trees_out::core_bools): Stream out new bit > decl_not_flexarray. > (trees_in::core_bools): Stream in new bit decl_not_flexarray. > > gcc/ChangeLog: > > * doc/extend.texi: Document strict_flex_array attribute. > * doc/invoke.texi: Document -fstrict-flex-array[=n] option. > * print-tree.cc (print_node): Print new bit decl_not_flexarray. > * tree-core.h (struct tree_decl_common): New bit field > decl_not_flexarray. > * tree-streamer-in.cc (unpack_ts_decl_common_value_fields): Stream > in new bit decl_not_flexarray. > * tree-streamer-out.cc (pack_ts_decl_common_value_fields): Stream > out new bit decl_not_flexarray. > * tree.cc (array_at_struct_end_p): Update it with the new bit field > decl_not_flexarray. > * tree.h (DECL_NOT_FLEXARRAY): New fla
The middle-end changes are OK, the c/ and cp/ changes need review from a frontend maintainer. Are the testcases actually C/C++ code? You can use testsuite/c-c++-common/ to place tests that run with both frontends. Richard. > > gcc/testsuite/ChangeLog: > > * g++.dg/strict-flex-array-1.C: New test. > * g++.dg/strict-flex-array-2.C: New test. > * g++.dg/strict-flex-array-3.C: New test. > * g++.dg/strict-flex-array-4.C: New test. > * gcc.dg/strict-flex-array-1.c: New test. > * gcc.dg/strict-flex-array-2.c: New test. > * gcc.dg/strict-flex-array-3.c: New test. > * gcc.dg/strict-flex-array-4.c: New test. > --- > gcc/c-family/c-attribs.cc | 94 +++++++++++++++ > gcc/c-family/c-opts.cc | 41 +++++++ > gcc/c-family/c.opt | 7 ++ > gcc/c/c-decl.cc | 130 +++++++++++++++++++-- > gcc/cp/module.cc | 2 + > gcc/doc/extend.texi | 33 ++++++ > gcc/doc/invoke.texi | 34 +++++- > gcc/print-tree.cc | 8 +- > gcc/testsuite/g++.dg/strict-flex-array-1.C | 31 +++++ > gcc/testsuite/g++.dg/strict-flex-array-2.C | 16 +++ > gcc/testsuite/g++.dg/strict-flex-array-3.C | 21 ++++ > gcc/testsuite/g++.dg/strict-flex-array-4.C | 9 ++ > gcc/testsuite/gcc.dg/strict-flex-array-1.c | 31 +++++ > gcc/testsuite/gcc.dg/strict-flex-array-2.c | 15 +++ > gcc/testsuite/gcc.dg/strict-flex-array-3.c | 21 ++++ > gcc/testsuite/gcc.dg/strict-flex-array-4.c | 10 ++ > gcc/tree-core.h | 5 +- > gcc/tree-streamer-in.cc | 1 + > gcc/tree-streamer-out.cc | 1 + > gcc/tree.cc | 45 +++++-- > gcc/tree.h | 14 ++- > 21 files changed, 541 insertions(+), 28 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-1.C > create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-2.C > create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-3.C > create mode 100644 gcc/testsuite/g++.dg/strict-flex-array-4.C > create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-1.c > create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-2.c > create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-3.c > create mode 100644 gcc/testsuite/gcc.dg/strict-flex-array-4.c > > diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc > index e4f1d3542f37..9c9927cefa0d 100644 > --- a/gcc/c-family/c-attribs.cc > +++ b/gcc/c-family/c-attribs.cc > @@ -101,6 +101,8 @@ static tree handle_special_var_sec_attribute (tree *, > tree, tree, int, bool *); > static tree handle_aligned_attribute (tree *, tree, tree, int, bool *); > static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree, > int, bool *); > +static tree handle_strict_flex_arrays_attribute (tree *, tree, tree, > + int, bool *); > static tree handle_weak_attribute (tree *, tree, tree, int, bool *) ; > static tree handle_noplt_attribute (tree *, tree, tree, int, bool *) ; > static tree handle_alias_ifunc_attribute (bool, tree *, tree, tree, bool *); > @@ -368,6 +370,8 @@ const struct attribute_spec c_common_attribute_table[] = > attr_aligned_exclusions }, > { "warn_if_not_aligned", 0, 1, false, false, false, false, > handle_warn_if_not_aligned_attribute, NULL }, > + { "strict_flex_arrays", 1, 1, false, false, false, false, > + handle_strict_flex_arrays_attribute, NULL }, > { "weak", 0, 0, true, false, false, false, > handle_weak_attribute, NULL }, > { "noplt", 0, 0, true, false, false, false, > @@ -2505,6 +2509,96 @@ handle_warn_if_not_aligned_attribute (tree *node, tree > name, > no_add_attrs, true); > } > > +/* Handle a "strict_flex_arrays" attribute; arguments as in > + struct attribute_spec.handler. */ > + > +static tree > +handle_strict_flex_arrays_attribute (tree *node, tree name, > + tree args, int ARG_UNUSED (flags), > + bool *no_add_attrs) > +{ > + tree decl = *node; > + tree argval = TREE_VALUE (args); > + > + /* This attribute only applies to field decls of a structure. */ > + if (TREE_CODE (decl) != FIELD_DECL) > + { > + error_at (DECL_SOURCE_LOCATION (decl), > + "%qE attribute may not be specified for %q+D", name, decl); > + *no_add_attrs = true; > + } > + /* This attribute only applies to field with array type. */ > + else if (TREE_CODE (TREE_TYPE (decl)) != ARRAY_TYPE) > + { > + error_at (DECL_SOURCE_LOCATION (decl), > + "%qE attribute may not be specified for a non array field", > + name); > + *no_add_attrs = true; > + } > + else if (TREE_CODE (argval) != INTEGER_CST) > + { > + error_at (DECL_SOURCE_LOCATION (decl), > + "%qE attribute argument not an integer", name); > + *no_add_attrs = true; > + } > + else if (!tree_fits_uhwi_p (argval) || tree_to_uhwi (argval) > 3) > + { > + error_at (DECL_SOURCE_LOCATION (decl), > + "%qE attribute argument %qE is not an integer constant" > + " between 0 and 3", name, argval); > + *no_add_attrs = true; > + } > + else > + { > + unsigned int level = tree_to_uhwi (argval); > + /* check whether the attribute is valid based on language standard. > + the attribute is only valid when flexible array member is > + supported in the language. Therefore, we should invalid this attribute > or > + specific level of this attribute for the following situations: > + A. When -std=c89 is specified, no language support at all, invalid this > + attribute and issue a warning; > + B. When -std=gnu89 is specified, only zero-length array extension and > + one-size array are supported, level=3 will be invalid and a warning > + will be issued. > + C. C++ without GNU extension, no language support at all, invalid this > + attribute and issue a warning; > + D. C++ with GNU extension, only zero-length array extension and one-size > + array are supported, level=3 will be invalid and a warning will be > + issued. */ > + if (level > 0) > + { > + if (!c_dialect_cxx () && flag_iso && flag_isoc99 == 0) > + { > + warning (OPT_Wattributes, "%qE attribute ignored since it is " > + "not supported with a ISO C before C99", name); > + *no_add_attrs = true; > + } > + else if (!c_dialect_cxx () && !flag_iso > + && flag_isoc99 == 0 && level == 3) > + { > + warning (OPT_Wattributes, "%qE = 3 attribute ignored since it is " > + "not supported with a GNU extension GNU89", name); > + *no_add_attrs = true; > + } > + else if (c_dialect_cxx () && flag_iso) > + { > + warning (OPT_Wattributes, "%qE attribute ignored since it is " > + "not supported with a ISO C++", name); > + *no_add_attrs = true; > + } > + else if (c_dialect_cxx () && !flag_iso > + && level == 3) > + { > + warning (OPT_Wattributes, "%qE = 3 attribute ignored since it is " > + "not supported for C++ with GNU extension", name); > + *no_add_attrs = true; > + } > + } > + } > + > + return NULL_TREE; > +} > + > /* Handle a "weak" attribute; arguments as in > struct attribute_spec.handler. */ > > diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc > index 4e1463689de3..639eb40f3c86 100644 > --- a/gcc/c-family/c-opts.cc > +++ b/gcc/c-family/c-opts.cc > @@ -870,6 +870,47 @@ c_common_post_options (const char **pfilename) > SET_OPTION_IF_UNSET (&global_options, &global_options_set, > flag_tree_loop_distribute_patterns, 0); > > + /* -fstrict-flex-arrays is only valid when flexible array member is > + supported in the language. Therefore, we should invalid this option or > + specific level of this option for the following situations: > + A. When -std=c89 is specified, no language support at all, invalid this > + option and issue a warning; > + B. When -std=gnu89 is specified, only zero-length array extension and > + one-size array are supported, level=3 will be invalid and a warning > + will be issued. > + C. C++ without GNU extension, no language support at all, invalid this > + option and issue a warning; > + D. C++ with GNU extension, only zero-length array extension and one-size > + array are supported, level=3 will be invalid and a warning will be > + issued. */ > + if (flag_strict_flex_arrays > 0) > + { > + if (!c_dialect_cxx () && flag_iso && flag_isoc99 == 0) > + { > + flag_strict_flex_arrays = 0; > + warning (0, "%<-fstrict-flex-arrays%> is not supported with a ISO C " > + "before C99, ignored"); > + } > + else if (!c_dialect_cxx () && !flag_iso && flag_isoc99 == 0 && > flag_strict_flex_arrays == 3) > + { > + flag_strict_flex_arrays = 0; > + warning (0, "%<-fstrict-flex-arrays=3%> is not supported with a " > + "GNU extension GNU89, ignored"); > + } > + else if (c_dialect_cxx () && flag_iso) > + { > + flag_strict_flex_arrays = 0; > + warning (0, "%<-fstrict-flex-arrays%> is not supported with a ISO " > + "C++, ignored"); > + } > + else if (c_dialect_cxx () && !flag_iso && flag_strict_flex_arrays == 3) > + { > + flag_strict_flex_arrays = 0; > + warning (0, "%<-fstrict-flex-arrays=3%> is not supported for C++ " > + "with GNU extension, ignored"); > + } > + } > + > /* -Woverlength-strings is off by default, but is enabled by -Wpedantic. > It is never enabled in C++, as the minimum limit is not normative > in that standard. */ > diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt > index 44e1a60ce246..1e944f8a3055 100644 > --- a/gcc/c-family/c.opt > +++ b/gcc/c-family/c.opt > @@ -2060,6 +2060,13 @@ fsized-deallocation > C++ ObjC++ Var(flag_sized_deallocation) Init(-1) > Enable C++14 sized deallocation support. > > +fstrict-flex-arrays > +C C++ Common Alias(fstrict-flex-arrays=,3,0) > + > +fstrict-flex-arrays= > +C C++ Common Joined RejectNegative UInteger Var(flag_strict_flex_arrays) > Init(0) IntegerRange(0,3) > +-fstrict-flex-arrays=<level> Treat the trailing array of a structure as a > flexible array in a stricter way. The default is treating all trailing > arrays of structures as flexible arrays. > + > fsquangle > C++ ObjC++ WarnRemoved > > diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc > index ae8990c138fd..a2e125d4ddd5 100644 > --- a/gcc/c/c-decl.cc > +++ b/gcc/c/c-decl.cc > @@ -4999,6 +4999,41 @@ set_array_declarator_inner (struct c_declarator *decl, > return decl; > } > > +/* Determine whether TYPE is a ISO C99 flexible array memeber type "[]". */ > +static bool > +flexible_array_member_type_p (const_tree type) > +{ > + if (TREE_CODE (type) == ARRAY_TYPE > + && TYPE_SIZE (type) == NULL_TREE > + && TYPE_DOMAIN (type) != NULL_TREE > + && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE) > + return true; > + > + return false; > +} > + > +/* Determine whether TYPE is a one-element array type "[1]". */ > +static bool > +one_element_array_type_p (const_tree type) > +{ > + if (TREE_CODE (type) != ARRAY_TYPE) > + return false; > + return integer_zerop (array_type_nelts (type)); > +} > + > +/* Determine whether TYPE is a zero-length array type "[0]". */ > +static bool > +zero_length_array_type_p (const_tree type) > +{ > + if (TREE_CODE (type) == ARRAY_TYPE) > + if (tree type_size = TYPE_SIZE_UNIT (type)) > + if ((integer_zerop (type_size)) > + && TYPE_DOMAIN (type) != NULL_TREE > + && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE) > + return true; > + return false; > +} > + > /* INIT is a constructor that forms DECL's initializer. If the final > element initializes a flexible array field, add the size of that > initializer to DECL's size. */ > @@ -5013,10 +5048,7 @@ add_flexible_array_elts_to_size (tree decl, tree init) > > elt = CONSTRUCTOR_ELTS (init)->last ().value; > type = TREE_TYPE (elt); > - if (TREE_CODE (type) == ARRAY_TYPE > - && TYPE_SIZE (type) == NULL_TREE > - && TYPE_DOMAIN (type) != NULL_TREE > - && TYPE_MAX_VALUE (TYPE_DOMAIN (type)) == NULL_TREE) > + if (flexible_array_member_type_p (type)) > { > complete_array_type (&type, elt, false); > DECL_SIZE (decl) > @@ -8720,6 +8752,81 @@ finish_incomplete_vars (tree incomplete_vars, bool > toplevel) > } > } > > + > +/* Determine whether the FIELD_DECL X is a flexible array member according to > + the following info: > + A. whether the FIELD_DECL X is the last field of the DECL_CONTEXT; > + B. whether the FIELD_DECL is an array that is declared as "[]", "[0]", > + or "[1]"; > + C. flag_strict_flex_arrays; > + D. the attribute strict_flex_array that is attached to the field > + if presenting. > + Return TRUE when it's a flexible array member, FALSE otherwise. */ > + > +static bool > +is_flexible_array_member_p (bool is_last_field, > + tree x) > +{ > + /* if not the last field, return false. */ > + if (!is_last_field) > + return false; > + > + /* if not an array field, return false. */ > + if (TREE_CODE (TREE_TYPE (x)) != ARRAY_TYPE) > + return false; > + > + bool is_zero_length_array = zero_length_array_type_p (TREE_TYPE (x)); > + bool is_one_element_array = one_element_array_type_p (TREE_TYPE (x)); > + bool is_flexible_array = flexible_array_member_type_p (TREE_TYPE (x)); > + > + unsigned int strict_flex_array_level = flag_strict_flex_arrays; > + > + tree attr_strict_flex_array = lookup_attribute ("strict_flex_arrays", > + DECL_ATTRIBUTES (x)); > + /* if there is a strict_flex_array attribute attached to the field, > + override the flag_strict_flex_arrays. */ > + if (attr_strict_flex_array) > + { > + /* get the value of the level first from the attribute. */ > + unsigned HOST_WIDE_INT attr_strict_flex_array_level = 0; > + gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE); > + attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array); > + gcc_assert (TREE_VALUE (attr_strict_flex_array) != NULL_TREE); > + attr_strict_flex_array = TREE_VALUE (attr_strict_flex_array); > + gcc_assert (tree_fits_uhwi_p (attr_strict_flex_array)); > + attr_strict_flex_array_level = tree_to_uhwi (attr_strict_flex_array); > + > + /* the attribute has higher priority than flag_struct_flex_array. */ > + strict_flex_array_level = attr_strict_flex_array_level; > + } > + > + switch (strict_flex_array_level) > + { > + case 0: > + /* default, all trailing arrays are flexiable array members. */ > + return true; > + case 1: > + /* Level 1: all "[1]", "[0]", and "[]" are flexiable array members. */ > + if (is_one_element_array) > + return true; > + /* FALLTHROUGH. */ > + case 2: > + /* Level 2: all "[0]", and "[]" are flexiable array members. */ > + if (is_zero_length_array) > + return true; > + /* FALLTHROUGH. */ > + case 3: > + /* Level 3: Only "[]" are flexible array members. */ > + if (is_flexible_array) > + return true; > + break; > + default: > + gcc_unreachable (); > + } > + return false; > +} > + > + > /* Fill in the fields of a RECORD_TYPE or UNION_TYPE node, T. > LOC is the location of the RECORD_TYPE or UNION_TYPE's definition. > FIELDLIST is a chain of FIELD_DECL nodes for the fields. > @@ -8781,6 +8888,11 @@ finish_struct (location_t loc, tree t, tree fieldlist, > tree attributes, > bool saw_named_field = false; > for (x = fieldlist; x; x = DECL_CHAIN (x)) > { > + /* whether this field is the last field of the structure or union. > + for UNION, any field is the last field of it. */ > + bool is_last_field = (DECL_CHAIN (x) == NULL_TREE) > + || (TREE_CODE (t) == UNION_TYPE); > + > if (TREE_TYPE (x) == error_mark_node) > continue; > > @@ -8819,10 +8931,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, > tree attributes, > DECL_PACKED (x) = 1; > > /* Detect flexible array member in an invalid context. */ > - if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE > - && TYPE_SIZE (TREE_TYPE (x)) == NULL_TREE > - && TYPE_DOMAIN (TREE_TYPE (x)) != NULL_TREE > - && TYPE_MAX_VALUE (TYPE_DOMAIN (TREE_TYPE (x))) == NULL_TREE) > + if (flexible_array_member_type_p (TREE_TYPE (x))) > { > if (TREE_CODE (t) == UNION_TYPE) > { > @@ -8830,7 +8939,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, > tree attributes, > "flexible array member in union"); > TREE_TYPE (x) = error_mark_node; > } > - else if (DECL_CHAIN (x) != NULL_TREE) > + else if (!is_last_field) > { > error_at (DECL_SOURCE_LOCATION (x), > "flexible array member not at end of struct"); > @@ -8850,6 +8959,9 @@ finish_struct (location_t loc, tree t, tree fieldlist, > tree attributes, > pedwarn (DECL_SOURCE_LOCATION (x), OPT_Wpedantic, > "invalid use of structure with flexible array member"); > > + /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x. */ > + DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field, > x); > + > if (DECL_NAME (x) > || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x))) > saw_named_field = true; > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc > index f27f4d091e5e..75ee2514f66b 100644 > --- a/gcc/cp/module.cc > +++ b/gcc/cp/module.cc > @@ -5414,6 +5414,7 @@ trees_out::core_bools (tree t) > WB (t->decl_common.decl_by_reference_flag); > WB (t->decl_common.decl_read_flag); > WB (t->decl_common.decl_nonshareable_flag); > + WB (t->decl_common.decl_not_flexarray); > } > > if (CODE_CONTAINS_STRUCT (code, TS_DECL_WITH_VIS)) > @@ -5558,6 +5559,7 @@ trees_in::core_bools (tree t) > RB (t->decl_common.decl_by_reference_flag); > RB (t->decl_common.decl_read_flag); > RB (t->decl_common.decl_nonshareable_flag); > + RB (t->decl_common.decl_not_flexarray); > } > > if (CODE_CONTAINS_STRUCT (code, TS_DECL_WITH_VIS)) > diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi > index 7fe7f8817cdd..99b43ed3852c 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > @@ -7473,6 +7473,39 @@ This warning can be disabled by > @option{-Wno-if-not-aligned}. > The @code{warn_if_not_aligned} attribute can also be used for types > (@pxref{Common Type Attributes}.) > > +@cindex @code{strict_flex_arrays} variable attribute > +@item strict_flex_arrays (@var{level}) > +The @code{strict_flex_arrays} attribute should be attached to the trailing > +array field of a structure. It specifies the level of strictness of > +treating the trailing array field of a structure as a flexible array > +member. @var{level} must be an integer betwen 0 to 3. > + > +@var{level}=0 is the least strict level, all trailing arrays of structures > +are treated as flexible array members. @var{level}=3 is the strictest level, > +only when the trailing array is declared as a flexible array member per C99 > +standard onwards ([]), it is treated as a flexible array member. > + > +There are two more levels in between 0 and 3, which are provided to support > +older codes that use GCC zero-length array extension ([0]) or one-size array > +as flexible array member ([1]): > +When @var{level} is 1, the trailing array is treated as a flexible array > member > +when it is declared as either "[]", "[0]", or "[1]"; > +When @var{level} is 2, the trailing array is treated as a flexible array > member > +when it is declared as either "[]", or "[0]". > + > +This attribute can be used with or without the @option{-fstrict-flex-arrays}. > +When both the attribute and the option present at the same time, the level of > +the strictness for the specific trailing array field is determined by the > +attribute. > + > +This attribute is only valid when flexible array member is supported in the > +language. For ISO C before C99 and ISO C++, no language support for the > flexible > +array member at all, this attribute will be invalid and a warning is issued. > +When -std=gnu89 is specified or C++ with GNU extension, only zero-length > array > +extension and one-size array are supported, as a result, @var{level}=3 will > be > +invalid and a warning is issued. > + > + > @item alloc_size (@var{position}) > @itemx alloc_size (@var{position-1}, @var{position-2}) > @cindex @code{alloc_size} variable attribute > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > index 863580b3710a..2a0a3cf3de10 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -207,7 +207,8 @@ in the following sections. > -fopenmp -fopenmp-simd @gol > -fpermitted-flt-eval-methods=@var{standard} @gol > -fplan9-extensions -fsigned-bitfields -funsigned-bitfields @gol > --fsigned-char -funsigned-char -fsso-struct=@var{endianness}} > +-fsigned-char -funsigned-char -fstrict-flex-arrays[=@var{n}] @gol > +-fsso-struct=@var{endianness}} > > @item C++ Language Options > @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. > @@ -2826,6 +2827,37 @@ The type @code{char} is always a distinct type from > each of > @code{signed char} or @code{unsigned char}, even though its behavior > is always just like one of those two. > > +@item -fstrict-flex-arrays > +@opindex fstrict-flex-arrays > +@opindex fno-strict-flex-arrays > +Treat the trailing array of a structure as a flexible array member in a > +stricter way. > +The positive form is equivalent to @option{-fstrict-flex-arrays=3}, which is > the > +strictest. A trailing array is treated as a flexible array member only when > it > +is declared as a flexible array member per C99 standard onwards. > +The negative form is equivalent to @option{-fstrict-flex-arrays=0}, which is > the > +least strict. All trailing arrays of structures are treated as flexible > array > +members. > + > +@item -fstrict-flex-arrays=@var{level} > +@opindex fstrict-flex-arrays=@var{level} > +Treat the trailing array of a structure as a flexible array member in a > +stricter way. The value of @var{level} controls the level of strictness. > + > +The possible values of @var{level} are the same as for the > +@code{strict_flex_array} attribute (@pxref{Variable Attributes}). > + > +You can control this behavior for a specific trailing array field of a > +structure by using the variable attribute @code{strict_flex_array} attribute > +(@pxref{Variable Attributes}). > + > +This option is only valid when flexible array member is supported in the > +language. FOR ISO C before C99 and ISO C++, no language support for the > flexible > +array member at all, this option will be invalid and a warning will be > issued. > +When -std=gnu89 is specified or C++ with GNU extension, only zero-length > array > +extension and one-size array are supported, as a result, @var{level}=3 will > be > +invalid and a warning will be issued. > + > @item -fsso-struct=@var{endianness} > @opindex fsso-struct > Set the default scalar storage order of structures and unions to the > diff --git a/gcc/print-tree.cc b/gcc/print-tree.cc > index 6d45a4a59669..58a98250cc4f 100644 > --- a/gcc/print-tree.cc > +++ b/gcc/print-tree.cc > @@ -517,8 +517,12 @@ print_node (FILE *file, const char *prefix, tree node, > int indent, > fprintf (file, " align:%d warn_if_not_align:%d", > DECL_ALIGN (node), DECL_WARN_IF_NOT_ALIGN (node)); > if (code == FIELD_DECL) > - fprintf (file, " offset_align " HOST_WIDE_INT_PRINT_UNSIGNED, > - DECL_OFFSET_ALIGN (node)); > + { > + fprintf (file, " offset_align " HOST_WIDE_INT_PRINT_UNSIGNED, > + DECL_OFFSET_ALIGN (node)); > + fprintf (file, " decl_not_flexarray: %d", > + DECL_NOT_FLEXARRAY (node)); > + } > > if (code == FUNCTION_DECL && fndecl_built_in_p (node)) > { > diff --git a/gcc/testsuite/g++.dg/strict-flex-array-1.C > b/gcc/testsuite/g++.dg/strict-flex-array-1.C > new file mode 100644 > index 000000000000..47adaf7bac4a > --- /dev/null > +++ b/gcc/testsuite/g++.dg/strict-flex-array-1.C > @@ -0,0 +1,31 @@ > +/* testing the correct usage of attribute strict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2" } */ > + > + > +int x __attribute__ ((strict_flex_arrays (1))); /* { dg-error > "'strict_flex_arrays' attribute may not be specified for 'x'" } */ > + > +struct trailing { > + int a; > + int c __attribute ((strict_flex_arrays)); /* { dg-error "wrong number of > arguments specified for 'strict_flex_arrays' attribute" } */ > +}; > + > +struct trailing_1 { > + int a; > + int b; > + int c __attribute ((strict_flex_arrays (2))); /* { dg-error > "'strict_flex_arrays' attribute may not be specified for a non array field" } > */ > +}; > + > +extern int d; > + > +struct trailing_array_2 { > + int a; > + int b; > + int c[1] __attribute ((strict_flex_arrays (d))); /* { dg-error > "'strict_flex_arrays' attribute argument not an integer" } */ > +}; > + > +struct trailing_array_3 { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (5))); /* { dg-error > "'strict_flex_arrays' attribute argument '5' is not an integer constant > between 0 and 3" } */ > +}; > diff --git a/gcc/testsuite/g++.dg/strict-flex-array-2.C > b/gcc/testsuite/g++.dg/strict-flex-array-2.C > new file mode 100644 > index 000000000000..245f8fe0bc73 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/strict-flex-array-2.C > @@ -0,0 +1,16 @@ > +/* testing the correct usage of flag -fstrict_flex_array for C++. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays -std=c++98" } */ > + > +struct trailing_array { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning > "attribute ignored since it is not supported with a ISO C\\+\\+" } */ > +}; > + > +int foo(int a) > +{ > + return 0; > +} > + > +/* { dg-warning "is not supported with a ISO C\\+\\+, ignored" "" { target > *-*-* } 0 } */ > diff --git a/gcc/testsuite/g++.dg/strict-flex-array-3.C > b/gcc/testsuite/g++.dg/strict-flex-array-3.C > new file mode 100644 > index 000000000000..2a733a5bccf4 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/strict-flex-array-3.C > @@ -0,0 +1,21 @@ > +/* testing the correct usage of flag -fstrict_flex_array for C++. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays -std=gnu++98" } */ > +/* { dg-warning "'-fstrict-flex-arrays=3' is not supported for C\\+\\+ with > GNU extension, ignored" "" { target *-*-* } 0 } */ > + > +struct trailing_array { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning > "'strict_flex_arrays' = 3 attribute ignored since it is not supported for > C\\+\\+ with GNU extension" } */ > +}; > + > +struct trailing_array_1 { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (2))); /* { dg-bogus > "'strict_flex_arrays' = 3 attribute ignored since it is not supported for > C\\+\\+ with GNU extension" } */ > +}; > + > +int foo(int a) > +{ > + return a + 2; > +} > diff --git a/gcc/testsuite/g++.dg/strict-flex-array-4.C > b/gcc/testsuite/g++.dg/strict-flex-array-4.C > new file mode 100644 > index 000000000000..804e4cf459ef > --- /dev/null > +++ b/gcc/testsuite/g++.dg/strict-flex-array-4.C > @@ -0,0 +1,9 @@ > +/* testing the correct usage of flag -fstrict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays=2 -std=gnu++98" } */ > +/* { dg-bogus "is not supported for C\\+\\+ with GNU extension, ignored" "" > { target *-*-* } 0 } */ > + > +int foo(int a) > +{ > + return a + 2; > +} > diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-1.c > b/gcc/testsuite/gcc.dg/strict-flex-array-1.c > new file mode 100644 > index 000000000000..47adaf7bac4a > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/strict-flex-array-1.c > @@ -0,0 +1,31 @@ > +/* testing the correct usage of attribute strict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2" } */ > + > + > +int x __attribute__ ((strict_flex_arrays (1))); /* { dg-error > "'strict_flex_arrays' attribute may not be specified for 'x'" } */ > + > +struct trailing { > + int a; > + int c __attribute ((strict_flex_arrays)); /* { dg-error "wrong number of > arguments specified for 'strict_flex_arrays' attribute" } */ > +}; > + > +struct trailing_1 { > + int a; > + int b; > + int c __attribute ((strict_flex_arrays (2))); /* { dg-error > "'strict_flex_arrays' attribute may not be specified for a non array field" } > */ > +}; > + > +extern int d; > + > +struct trailing_array_2 { > + int a; > + int b; > + int c[1] __attribute ((strict_flex_arrays (d))); /* { dg-error > "'strict_flex_arrays' attribute argument not an integer" } */ > +}; > + > +struct trailing_array_3 { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (5))); /* { dg-error > "'strict_flex_arrays' attribute argument '5' is not an integer constant > between 0 and 3" } */ > +}; > diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-2.c > b/gcc/testsuite/gcc.dg/strict-flex-array-2.c > new file mode 100644 > index 000000000000..967a240040dc > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/strict-flex-array-2.c > @@ -0,0 +1,15 @@ > +/* testing the correct usage of flag -fstrict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays -std=c89" } */ > +/* { dg-warning "'-fstrict-flex-arrays' is not supported with a ISO C before > C99, ignored" "" { target *-*-* } 0 } */ > + > +struct trailing_array { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning > "'strict_flex_arrays' attribute ignored since it is not supported with a ISO > C before C99" } */ > +}; > + > +int foo(int a) > +{ > + return a + 2; > +} > diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-3.c > b/gcc/testsuite/gcc.dg/strict-flex-array-3.c > new file mode 100644 > index 000000000000..879de7f203c8 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/strict-flex-array-3.c > @@ -0,0 +1,21 @@ > +/* testing the correct usage of flag -fstrict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays -std=gnu89" } */ > +/* { dg-warning "'-fstrict-flex-arrays=3' is not supported with a GNU > extension GNU89, ignored" "" { target *-*-* } 0 } */ > + > +struct trailing_array { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (3))); /* { dg-warning > "'strict_flex_arrays' = 3 attribute ignored since it is not supported with a > GNU extension GNU89" } */ > +}; > + > +struct trailing_array_1 { > + int a; > + int b; > + int c[0] __attribute ((strict_flex_arrays (2))); /* { dg-bogus > "'strict_flex_arrays' = 3 attribute ignored since it is not supported with a > GNU extension GNU89" } */ > +}; > + > +int foo(int a) > +{ > + return a + 2; > +} > diff --git a/gcc/testsuite/gcc.dg/strict-flex-array-4.c > b/gcc/testsuite/gcc.dg/strict-flex-array-4.c > new file mode 100644 > index 000000000000..ce64c24db301 > --- /dev/null > +++ b/gcc/testsuite/gcc.dg/strict-flex-array-4.c > @@ -0,0 +1,10 @@ > +/* testing the correct usage of flag -fstrict_flex_array. */ > +/* { dg-do compile } */ > +/* { dg-options "-O2 -fstrict-flex-arrays=2 -std=gnu89" } */ > +/* { dg-bogus "is not supported with a GNU extension GNU89, ignored" "" { > target *-*-* } 0 } */ > + > + > +int foo(int a) > +{ > + return a + 2; > +} > diff --git a/gcc/tree-core.h b/gcc/tree-core.h > index 86a07c282af2..f822cb539dd0 100644 > --- a/gcc/tree-core.h > +++ b/gcc/tree-core.h > @@ -1813,7 +1813,10 @@ struct GTY(()) tree_decl_common { > TYPE_WARN_IF_NOT_ALIGN. */ > unsigned int warn_if_not_align : 6; > > - /* 14 bits unused. */ > + /* In FIELD_DECL, this is DECL_NOT_FLEXARRAY. */ > + unsigned int decl_not_flexarray : 1; > + > + /* 13 bits unused. */ > > /* UID for points-to sets, stable over copying from inlining. */ > unsigned int pt_uid; > diff --git a/gcc/tree-streamer-in.cc b/gcc/tree-streamer-in.cc > index 196f19c759f2..21e6e8eb1c0a 100644 > --- a/gcc/tree-streamer-in.cc > +++ b/gcc/tree-streamer-in.cc > @@ -261,6 +261,7 @@ unpack_ts_decl_common_value_fields (struct bitpack_d *bp, > tree expr) > else > SET_DECL_FIELD_ABI_IGNORED (expr, val); > expr->decl_common.off_align = bp_unpack_value (bp, 8); > + DECL_NOT_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1); > } > > else if (VAR_P (expr)) > diff --git a/gcc/tree-streamer-out.cc b/gcc/tree-streamer-out.cc > index d39dc158a465..68e40dbdb8f2 100644 > --- a/gcc/tree-streamer-out.cc > +++ b/gcc/tree-streamer-out.cc > @@ -229,6 +229,7 @@ pack_ts_decl_common_value_fields (struct bitpack_d *bp, > tree expr) > else > bp_pack_value (bp, DECL_FIELD_ABI_IGNORED (expr), 1); > bp_pack_value (bp, expr->decl_common.off_align, 8); > + bp_pack_value (bp, DECL_NOT_FLEXARRAY (expr), 1); > } > > else if (VAR_P (expr)) > diff --git a/gcc/tree.cc b/gcc/tree.cc > index fed1434d141d..d698e8c9c213 100644 > --- a/gcc/tree.cc > +++ b/gcc/tree.cc > @@ -12678,14 +12678,30 @@ array_ref_up_bound (tree exp) > } > > /* Returns true if REF is an array reference, component reference, > - or memory reference to an array at the end of a structure. > - If this is the case, the array may be allocated larger > - than its upper bound implies. */ > + or memory reference to an array whose actual size might be larger > + than its upper bound implies, there are multiple cases: > + A. a ref to a flexible array member at the end of a structure; > + B. a ref to an array with a different type against the original decl; > + for example: > > + short a[16] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 > }; > + (*((char(*)[16])&a[0]))[i+8] > + > + C. a ref to an array that was passed as a parameter; > + for example: > + > + int test (uint8_t *p, uint32_t t[1][1], int n) { > + for (int i = 0; i < 4; i++, p++) > + t[i][0] = ...; > + > + FIXME, the name of this routine need to be changed to be more accurate. > */ > bool > array_at_struct_end_p (tree ref) > { > - tree atype; > + /* the TYPE for this array referece. */ > + tree atype = NULL_TREE; > + /* the FIELD_DECL for the array field in the containing structure. */ > + tree afield_decl = NULL_TREE; > > if (TREE_CODE (ref) == ARRAY_REF > || TREE_CODE (ref) == ARRAY_RANGE_REF) > @@ -12695,7 +12711,10 @@ array_at_struct_end_p (tree ref) > } > else if (TREE_CODE (ref) == COMPONENT_REF > && TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 1))) == ARRAY_TYPE) > - atype = TREE_TYPE (TREE_OPERAND (ref, 1)); > + { > + atype = TREE_TYPE (TREE_OPERAND (ref, 1)); > + afield_decl = TREE_OPERAND (ref, 1); > + } > else if (TREE_CODE (ref) == MEM_REF) > { > tree arg = TREE_OPERAND (ref, 0); > @@ -12707,6 +12726,7 @@ array_at_struct_end_p (tree ref) > if (tree fld = last_field (argtype)) > { > atype = TREE_TYPE (fld); > + afield_decl = fld; > if (TREE_CODE (atype) != ARRAY_TYPE) > return false; > if (VAR_P (arg) && DECL_SIZE (fld)) > @@ -12760,13 +12780,16 @@ array_at_struct_end_p (tree ref) > ref = TREE_OPERAND (ref, 0); > } > > - /* The array now is at struct end. Treat flexible arrays as > + gcc_assert (!afield_decl > + || (afield_decl && TREE_CODE (afield_decl) == FIELD_DECL)); > + > + /* The array now is at struct end. Treat flexible array member as > always subject to extend, even into just padding constrained by > an underlying decl. */ > if (! TYPE_SIZE (atype) > || ! TYPE_DOMAIN (atype) > || ! TYPE_MAX_VALUE (TYPE_DOMAIN (atype))) > - return true; > + return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true; > > /* If the reference is based on a declared entity, the size of the array > is constrained by its given domain. (Do not trust commons PR/69368). > */ > @@ -12788,9 +12811,9 @@ array_at_struct_end_p (tree ref) > if (TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (atype))) != INTEGER_CST > || TREE_CODE (TYPE_MAX_VALUE (TYPE_DOMAIN (atype))) != INTEGER_CST > || TREE_CODE (TYPE_MIN_VALUE (TYPE_DOMAIN (atype))) != INTEGER_CST) > - return true; > + return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true; > if (! get_addr_base_and_unit_offset (ref_to_array, &offset)) > - return true; > + return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true; > > /* If at least one extra element fits it is a flexarray. */ > if (known_le ((wi::to_offset (TYPE_MAX_VALUE (TYPE_DOMAIN (atype))) > @@ -12798,12 +12821,12 @@ array_at_struct_end_p (tree ref) > + 2) > * wi::to_offset (TYPE_SIZE_UNIT (TREE_TYPE (atype))), > wi::to_offset (DECL_SIZE_UNIT (ref)) - offset)) > - return true; > + return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true; > > return false; > } > > - return true; > + return afield_decl ? !DECL_NOT_FLEXARRAY (afield_decl) : true; > } > > /* Return a tree representing the offset, in bytes, of the field referenced > diff --git a/gcc/tree.h b/gcc/tree.h > index e6564aaccb7b..f911c0a46e69 100644 > --- a/gcc/tree.h > +++ b/gcc/tree.h > @@ -2993,6 +2993,12 @@ extern void decl_value_expr_insert (tree, tree); > #define DECL_PADDING_P(NODE) \ > (FIELD_DECL_CHECK (NODE)->decl_common.decl_flag_3) > > +/* Used in a FIELD_DECL to indicate whether this field is not a flexible > + array member. This is only valid for the last array type field of a > + structure. */ > +#define DECL_NOT_FLEXARRAY(NODE) \ > + (FIELD_DECL_CHECK (NODE)->decl_common.decl_not_flexarray) > + > /* A numeric unique identifier for a LABEL_DECL. The UID allocation is > dense, unique within any one function, and may be used to index arrays. > If the value is -1, then no UID has been assigned. */ > @@ -5531,10 +5537,10 @@ extern tree component_ref_field_offset (tree); > returns null. */ > enum struct special_array_member > { > - none, /* Not a special array member. */ > - int_0, /* Interior array member with size zero. */ > - trail_0, /* Trailing array member with size zero. */ > - trail_1 /* Trailing array member with one element. */ > + none, /* Not a special array member. */ > + int_0, /* Interior array member with size zero. */ > + trail_0, /* Trailing array member with size zero. */ > + trail_1 /* Trailing array member with one element. */ > }; > > /* Return the size of the member referenced by the COMPONENT_REF, using > -- Richard Biener <rguent...@suse.de> SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg, Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman; HRB 36809 (AG Nuernberg)