GCC Extensions in TI Compilers (06Q1-10Q4)

Introduction

The GNU Compiler Collection (GCC) supports many language features not found in the ANSI/ISO standards for C and C++. The GCC compilers (gcc and g++) are widely used, particularly in open source applications. In order to allow users to compile code developed using the GCC tools, TI compilers can accept some GCC language extensions. This article describes the current state of support for the GCC extensions in the TI C/C++ compilers.

The TI compiler supports some of the extensions supported by GCC version 3.0.

At the time of writing (Sept. 2010), the current GCC release is GCC 4.5.

The following table shows when GCC extension support became available. See Production Compiler Releases for information on release availability.

Target	Initial Release	Compiler User’s Guide
ARM	4.4.0	spnu151
C2000	5.0.0	spru514
C5500	4.0.0	spru281
C6000	6.1.0	spru187
MSP430	2.0.0	slau132

For information on the GCC extension support of the latest releases of the TI compiler, see GCC Extensions in TI Compilers.

Older TI compilers do not support a GCC mode, and thus do not directly support GCC extensions. However, some C99 extensions in C89 mode are similar.

TI does not document the use or purpose of GCC extensions. The definition and examples of the language extensions may be found at the GNU documentation web site. The Optimizing C/C++ Compiler User’s Guide for your target has a section entitled GNU C Compiler Extensions which lists the supported extensions. As the support for GCC extensions has changed over time, make sure you refer to the correct version of the user's guide.

Enabling GCC Language Extensions

The GCC extensions are only available in GCC mode; you must use the option --gcc.

C vs C++

The GCC extensions supported by the TI compiler are only available in C.

Language Features

The following table of features is based on the list of extensions given at the GNU web site (GCC 4.5). Each feature name is a link to the corresponding GNU definition of the feature.

Key to Supported column

Code	Availability
--	Feature is not supported
yes	Feature is supported

Feature	Supported	Description
Statement Exprs	yes	Putting statements and declarations inside expressions
Local Labels	yes	Labels local to a block
Labels as Values	--	Getting pointers to labels, and computed gotos
Nested Functions	--	As in Algol and Pascal, lexical scoping of functions
Constructing Calls	--	Dispatching a call to another function.
Naming Types	yes	Giving a name to the type of some expression
Typeof	yes	typeof: referring to the type of an expression.
Generalized Lvalues	yes	Using '?:', ',' and casts in lvalues.
Conditionals	yes	Omitting the middle operand of a '?:' expression.
Long Long	yes	Double-word integers---long long int.
Complex	--	Data types for complex numbers.
Floating Types	--	Additional floating types.
Decimal Float	--	Decimal floating types.
Hex Floats	--	Hexadecimal floating-point constants.
Fixed-Point	--	Fixed-point types.
Named Address Spaces	--	Named address spaces.
Zero Length	yes	Zero-length arrays.
Variable Length	--	Arrays whose length is computed at run time. For alloca(), see GNU alloca in TI Compilers
Empty Structures	yes	Structures with no members.
Variadic Macros	yes	Macros with a variable number of arguments.
Escaped Newlines	--	Slightly looser rules for escaped newlines.
Multi-line Strings	yes	String literals with embedded newlines
Subscripting	yes	Any array can be subscripted, even if not an lvalue.
Pointer Arith	--	Arithmetic on void-pointers and function pointers.
Initializers	yes	Non-constant initializers.
Compound Literals	yes	Compound literals give structures, unions or arrays as values.
Designated Inits	--	Labeling elements of initializers.
Cast to Union	yes	Casting to union type from any member of the union.
Case Ranges	yes	'case 1 ... 9' and such.
Mixed Declarations	yes	Mixing declarations and code.
Function Attributes	yes	Declaring that functions have no side effects, or that they can never return. (See details below)
Attribute Syntax	yes	Formal syntax for attributes.
Function Prototypes	yes	Prototype declarations and old-style definitions.
C++ Comments	yes	C++ comments are recognized.
Dollar Signs	yes	Dollar sign is allowed in identifiers.
Character Escapes	yes	'\e' stands for the character <ESC>.
Variable Attributes	yes	Specifying attributes of variables. (See details below)
Type Attributes	yes	Specifying attributes of types. (See details below)
Alignment	yes	Inquiring about the alignment of a type or variable. (__alignof__)
Inline	yes	Defining inline functions (as fast as macros).
Extended Asm	--	Assembler instructions with C expressions as operands.
Constraints	--	Constraints for asm operands
Asm Labels	yes	Specifying the assembler name to use for a C symbol.
Explicit Reg Vars	--	Defining variables residing in specified registers.
Alternate Keywords	yes	__const__, __asm__, etc., for header files. (also __extension__)
Incomplete Enums	yes	Define an enum tag without specifying its values
Function Names	yes	Printable strings which are the name of the current function (__FUNCTION__, etc)
Return Address	yes	Getting the return or frame address of a function.
Vector Extensions	--	Using vector instructions through built-in functions.
Offsetof	--	Special syntax for implementing offsetof.
Atomic Builtins	--	Built-in functions for atomic memory access.
Object Size Checking	--	Built-in functions for limited buffer overflow checking.
Other Builtins	yes	Other built-in functions. (See details below)
Target Builtins	yes	Built-in functions specific to particular targets.
Target Format Checks	n/a	Format checks specific to particular targets. (Solaris-only)
Pragmas	--	Pragmas accepted by GCC.
Unnamed Fields	yes	Unnamed struct/union fields within structs/unions.
Thread-Local	--	Per-thread variables.
Binary constants	--	Binary constants using the '0b' prefix.

Notes

• Statement Expressions are not currently available in C++.

• The Naming Types feature was dropped after GCC 3.1, but is still supported in the TI compiler.

• For MSP430 the long long type is not supported.

• When the long long type is supported it is always available even in strict ANSI mode.

• The Multi-line Strings feature was dropped after GCC 3.2, but is still supported in the TI compiler.

• The Desiginated Inits feature is supported only for struct types.

• The following features were not rejected even though they were not supported by the compiler: Labels as Values, Hex Floats, Pointer Arith, Extended Asm, Constraints, and Explicit Reg Vars.

• Not all function attributes, variable attributes, type attributes, and builtin functions are supported. See the following sections for details on these features.

Attributes

Function Attributes

Function attribute definitions and examples at the GNU web site.

Supported Function Attributes

• deprecated
• section
• unused
• visibility (C60 EABI only)

Variable Attributes

Variable attribute definitions and examples at the GNU web site.

Supported Variable Attributes

• deprecated
• section
• unused

Type Attributes

Type attribute definitions and examples at the GNU web site.

Supported Type Attributes

• packed (enum types only)
• unused
• visibility (C60 EABI only)

Notes

• The packed (struct/union) attribute is also available for ARM Cortex M3 starting with version 4.6.1 and for Cortex R4 and A8 devices starting with version 4.7.0, but may not be used, directly or indirectly, on a bit-field.

Builtin Functions

Information about builtin functions at the GNU web site.

Supported Builtin Functions

• __builtin_constant_p
• __builtin_expect
• __builtin_frame_address
• __builtin_return_address

Notes

• The function __builtin_constant_p is not treated as compile-time constant.
• The function __builtin_expect does not provide optimization based on this construct.
• The functions __builtin_frame_address and __builtin_return_address always return zero.
• The function __builtin_llabs is available only on targets that support the type long long.
• The functions __builtin_sqrt and __builtin_sqrtf are available only for ARM with VFP hardware.