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Diffstat (limited to 'gcc/doc/extend.texi')
| -rw-r--r-- | gcc/doc/extend.texi | 43 |
1 files changed, 34 insertions, 9 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 08344960b52..ea60b57fbf6 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -2449,6 +2449,14 @@ language. Some details may vary for C++ and Objective-C@. Because of infelicities in the grammar for attributes, some forms described here may not be successfully parsed in all cases. +There are some problems with the semantics of attributes in C++. For +example, there are no manglings for attributes, although they may affect +code generation, so problems may arise when attributed types are used in +conjunction with templates or overloading. Similarly, @code{typeid} +does not distinguish between types with different attributes. Support +for attributes in C++ may be restricted in future to attributes on +declarations only, but not on nested declarators. + @xref{Function Attributes}, for details of the semantics of attributes applying to functions. @xref{Variable Attributes}, for details of the semantics of attributes applying to variables. @xref{Type Attributes}, @@ -2520,9 +2528,8 @@ defined is not complete until after the attribute specifiers. Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for -example in the case of a parameter declaration). In future, attribute -specifiers in some places may however apply to a particular declarator -within a declaration instead; these cases are noted below. Where an +example in the case of a parameter declaration), or to a particular declarator +within a declaration. Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not @@ -2597,11 +2604,11 @@ ignored. An attribute specifier list may appear at the start of a nested declarator. At present, there are some limitations in this usage: the -attributes apply to the identifier declared, rather than to a specific -declarator. When attribute specifiers follow the @code{*} of a pointer +attributes correctly apply to the declarator, but for most individual +attributes the semantics this implies are not implemented. +When attribute specifiers follow the @code{*} of a pointer declarator, they may be mixed with any type qualifiers present. -The following describes intended future -semantics which make this syntax more useful only. It will make the +The following describes the formal semantics of this syntax. It will make the most sense if you are familiar with the formal specification of declarators in the ISO C standard. @@ -2642,8 +2649,26 @@ char *__attribute__((aligned(8))) *f; @noindent specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''. -Note again that this describes intended future semantics, not current -implementation. +Note again that this does not work with most attributes; for example, +the usage of @samp{aligned} and @samp{noreturn} attributes given above +is not yet supported. + +For compatibility with existing code written for compiler versions that +did not implement attributes on nested declarators, some laxity is +allowed in the placing of attributes. If an attribute that only applies +to types is applied to a declaration, it will be treated as applying to +the type of that declaration. If an attribute that only applies to +declarations is applied to the type of a declaration, it will be treated +as applying to that declaration; and, for compatibility with code +placing the attributes immediately before the identifier declared, such +an attribute applied to a function return type will be treated as +applying to the function type, and such an attribute applied to an array +element type will be treated as applying to the array type. If an +attribute that only applies to function types is applied to a +pointer-to-function type, it will be treated as applying to the pointer +target type; if such an attribute is applied to a function return type +that is not a pointer-to-function type, it will be treated as applying +to the function type. @node Function Prototypes @section Prototypes and Old-Style Function Definitions |