Gcc/10.2.0/gcc/index

Using the GNU Compiler Collection (GCC)

This file documents the use of the GNU compilers.

Copyright © 1988-2020 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “Funding Free Software”, the Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled “GNU Free Documentation License”.

(a) The FSF’s Front-Cover Text is:

A GNU Manual

(b) The FSF’s Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.

Short Table of Contents

• 1 Programming Languages Supported by GCC
• 2 Language Standards Supported by GCC
• 3 GCC Command Options
• 4 C Implementation-Defined Behavior
• 5 C++ Implementation-Defined Behavior
• 6 Extensions to the C Language Family
• 7 Extensions to the C++ Language
• 8 GNU Objective-C Features
• 9 Binary Compatibility
• 10 gcov—a Test Coverage Program
• 11 gcov-tool—an Offline Gcda Profile Processing Tool
• 12 gcov-dump—an Offline Gcda and Gcno Profile Dump Tool
• 13 lto-dump—Tool for dumping LTO object files.
• 14 Known Causes of Trouble with GCC
• 15 Reporting Bugs
• 16 How To Get Help with GCC
• 17 Contributing to GCC Development
• Funding Free Software
• The GNU Project and GNU/Linux
• GNU General Public License
• GNU Free Documentation License
• Contributors to GCC
• Option Index
• Keyword Index

Table of Contents

• 1 Programming Languages Supported by GCC
• 2 Language Standards Supported by GCC
  • 2.1 C Language
  • 2.2 C++ Language
  • 2.3 Objective-C and Objective-C++ Languages
  • 2.4 Go Language
  • 2.5 HSA Intermediate Language (HSAIL)
  • 2.6 D language
  • 2.7 References for Other Languages
• 3 GCC Command Options
  • 3.1 Option Summary
  • 3.2 Options Controlling the Kind of Output
  • 3.3 Compiling C++ Programs
  • 3.4 Options Controlling C Dialect
  • 3.5 Options Controlling C++ Dialect
  • 3.6 Options Controlling Objective-C and Objective-C++ Dialects
  • 3.7 Options to Control Diagnostic Messages Formatting
  • 3.8 Options to Request or Suppress Warnings
  • 3.9 Options That Control Static Analysis
  • 3.10 Options for Debugging Your Program
  • 3.11 Options That Control Optimization
  • 3.12 Program Instrumentation Options
  • 3.13 Options Controlling the Preprocessor
  • 3.14 Passing Options to the Assembler
  • 3.15 Options for Linking
  • 3.16 Options for Directory Search
  • 3.17 Options for Code Generation Conventions
  • 3.18 GCC Developer Options
  • 3.19 Machine-Dependent Options
    • 3.19.1 AArch64 Options
      • 3.19.1.1 -march and -mcpu Feature Modifiers
    • 3.19.2 Adapteva Epiphany Options
    • 3.19.3 AMD GCN Options
    • 3.19.4 ARC Options
    • 3.19.5 ARM Options
    • 3.19.6 AVR Options
      • 3.19.6.1 EIND and Devices with More Than 128 Ki Bytes of Flash
      • 3.19.6.2 Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special Function Registers
      • 3.19.6.3 AVR Built-in Macros
    • 3.19.7 Blackfin Options
    • 3.19.8 C6X Options
    • 3.19.9 CRIS Options
    • 3.19.10 CR16 Options
    • 3.19.11 C-SKY Options
    • 3.19.12 Darwin Options
    • 3.19.13 DEC Alpha Options
    • 3.19.14 eBPF Options
    • 3.19.15 FR30 Options
    • 3.19.16 FT32 Options
    • 3.19.17 FRV Options
    • 3.19.18 GNU/Linux Options
    • 3.19.19 H8/300 Options
    • 3.19.20 HPPA Options
    • 3.19.21 IA-64 Options
    • 3.19.22 LM32 Options
    • 3.19.23 M32C Options
    • 3.19.24 M32R/D Options
    • 3.19.25 M680x0 Options
    • 3.19.26 MCore Options
    • 3.19.27 MeP Options
    • 3.19.28 MicroBlaze Options
    • 3.19.29 MIPS Options
    • 3.19.30 MMIX Options
    • 3.19.31 MN10300 Options
    • 3.19.32 Moxie Options
    • 3.19.33 MSP430 Options
    • 3.19.34 NDS32 Options
    • 3.19.35 Nios II Options
    • 3.19.36 Nvidia PTX Options
    • 3.19.37 OpenRISC Options
    • 3.19.38 PDP-11 Options
    • 3.19.39 picoChip Options
    • 3.19.40 PowerPC Options
    • 3.19.41 PRU Options
    • 3.19.42 RISC-V Options
    • 3.19.43 RL78 Options
    • 3.19.44 IBM RS/6000 and PowerPC Options
    • 3.19.45 RX Options
    • 3.19.46 S/390 and zSeries Options
    • 3.19.47 Score Options
    • 3.19.48 SH Options
    • 3.19.49 Solaris 2 Options
    • 3.19.50 SPARC Options
    • 3.19.51 Options for System V
    • 3.19.52 TILE-Gx Options
    • 3.19.53 TILEPro Options
    • 3.19.54 V850 Options
    • 3.19.55 VAX Options
    • 3.19.56 Visium Options
    • 3.19.57 VMS Options
    • 3.19.58 VxWorks Options
    • 3.19.59 x86 Options
    • 3.19.60 x86 Windows Options
    • 3.19.61 Xstormy16 Options
    • 3.19.62 Xtensa Options
    • 3.19.63 zSeries Options
  • 3.20 Specifying Subprocesses and the Switches to Pass to Them
  • 3.21 Environment Variables Affecting GCC
  • 3.22 Using Precompiled Headers
• 4 C Implementation-Defined Behavior
  • 4.1 Translation
  • 4.2 Environment
  • 4.3 Identifiers
  • 4.4 Characters
  • 4.5 Integers
  • 4.6 Floating Point
  • 4.7 Arrays and Pointers
  • 4.8 Hints
  • 4.9 Structures, Unions, Enumerations, and Bit-Fields
  • 4.10 Qualifiers
  • 4.11 Declarators
  • 4.12 Statements
  • 4.13 Preprocessing Directives
  • 4.14 Library Functions
  • 4.15 Architecture
  • 4.16 Locale-Specific Behavior
• 5 C++ Implementation-Defined Behavior
  • 5.1 Conditionally-Supported Behavior
  • 5.2 Exception Handling
• 6 Extensions to the C Language Family
  • 6.1 Statements and Declarations in Expressions
  • 6.2 Locally Declared Labels
  • 6.3 Labels as Values
  • 6.4 Nested Functions
  • 6.5 Nonlocal Gotos
  • 6.6 Constructing Function Calls
  • 6.7 Referring to a Type with typeof
  • 6.8 Conditionals with Omitted Operands
  • 6.9 128-bit Integers
  • 6.10 Double-Word Integers
  • 6.11 Complex Numbers
  • 6.12 Additional Floating Types
  • 6.13 Half-Precision Floating Point
  • 6.14 Decimal Floating Types
  • 6.15 Hex Floats
  • 6.16 Fixed-Point Types
  • 6.17 Named Address Spaces
    • 6.17.1 AVR Named Address Spaces
    • 6.17.2 M32C Named Address Spaces
    • 6.17.3 RL78 Named Address Spaces
    • 6.17.4 x86 Named Address Spaces
  • 6.18 Arrays of Length Zero
  • 6.19 Structures with No Members
  • 6.20 Arrays of Variable Length
  • 6.21 Macros with a Variable Number of Arguments.
  • 6.22 Slightly Looser Rules for Escaped Newlines
  • 6.23 Non-Lvalue Arrays May Have Subscripts
  • 6.24 Arithmetic on void- and Function-Pointers
  • 6.25 Pointer Arguments in Variadic Functions
  • 6.26 Pointers to Arrays with Qualifiers Work as Expected
  • 6.27 Non-Constant Initializers
  • 6.28 Compound Literals
  • 6.29 Designated Initializers
  • 6.30 Case Ranges
  • 6.31 Cast to a Union Type
  • 6.32 Mixed Declarations and Code
  • 6.33 Declaring Attributes of Functions
    • 6.33.1 Common Function Attributes
    • 6.33.2 AArch64 Function Attributes
      • 6.33.2.1 Inlining rules
    • 6.33.3 AMD GCN Function Attributes
    • 6.33.4 ARC Function Attributes
    • 6.33.5 ARM Function Attributes
    • 6.33.6 AVR Function Attributes
    • 6.33.7 Blackfin Function Attributes
    • 6.33.8 CR16 Function Attributes
    • 6.33.9 C-SKY Function Attributes
    • 6.33.10 Epiphany Function Attributes
    • 6.33.11 H8/300 Function Attributes
    • 6.33.12 IA-64 Function Attributes
    • 6.33.13 M32C Function Attributes
    • 6.33.14 M32R/D Function Attributes
    • 6.33.15 m68k Function Attributes
    • 6.33.16 MCORE Function Attributes
    • 6.33.17 MeP Function Attributes
    • 6.33.18 MicroBlaze Function Attributes
    • 6.33.19 Microsoft Windows Function Attributes
    • 6.33.20 MIPS Function Attributes
    • 6.33.21 MSP430 Function Attributes
    • 6.33.22 NDS32 Function Attributes
    • 6.33.23 Nios II Function Attributes
    • 6.33.24 Nvidia PTX Function Attributes
    • 6.33.25 PowerPC Function Attributes
    • 6.33.26 RISC-V Function Attributes
    • 6.33.27 RL78 Function Attributes
    • 6.33.28 RX Function Attributes
    • 6.33.29 S/390 Function Attributes
    • 6.33.30 SH Function Attributes
    • 6.33.31 Symbian OS Function Attributes
    • 6.33.32 V850 Function Attributes
    • 6.33.33 Visium Function Attributes
    • 6.33.34 x86 Function Attributes
    • 6.33.35 Xstormy16 Function Attributes
  • 6.34 Specifying Attributes of Variables
    • 6.34.1 Common Variable Attributes
    • 6.34.2 ARC Variable Attributes
    • 6.34.3 AVR Variable Attributes
    • 6.34.4 Blackfin Variable Attributes
    • 6.34.5 H8/300 Variable Attributes
    • 6.34.6 IA-64 Variable Attributes
    • 6.34.7 M32R/D Variable Attributes
    • 6.34.8 MeP Variable Attributes
    • 6.34.9 Microsoft Windows Variable Attributes
    • 6.34.10 MSP430 Variable Attributes
    • 6.34.11 Nvidia PTX Variable Attributes
    • 6.34.12 PowerPC Variable Attributes
    • 6.34.13 RL78 Variable Attributes
    • 6.34.14 V850 Variable Attributes
    • 6.34.15 x86 Variable Attributes
    • 6.34.16 Xstormy16 Variable Attributes
  • 6.35 Specifying Attributes of Types
    • 6.35.1 Common Type Attributes
    • 6.35.2 ARC Type Attributes
    • 6.35.3 ARM Type Attributes
    • 6.35.4 MeP Type Attributes
    • 6.35.5 PowerPC Type Attributes
    • 6.35.6 x86 Type Attributes
  • 6.36 Label Attributes
  • 6.37 Enumerator Attributes
  • 6.38 Statement Attributes
  • 6.39 Attribute Syntax
  • 6.40 Prototypes and Old-Style Function Definitions
  • 6.41 C++ Style Comments
  • 6.42 Dollar Signs in Identifier Names
  • 6.43 The Character ESC in Constants
  • 6.44 Determining the Alignment of Functions, Types or Variables
  • 6.45 An Inline Function is As Fast As a Macro
  • 6.46 When is a Volatile Object Accessed?
  • 6.47 How to Use Inline Assembly Language in C Code
    • 6.47.1 Basic Asm — Assembler Instructions Without Operands
    • 6.47.2 Extended Asm - Assembler Instructions with C Expression Operands
      • 6.47.2.1 Volatile
      • 6.47.2.2 Assembler Template
      • 6.47.2.3 Output Operands
      • 6.47.2.4 Flag Output Operands
      • 6.47.2.5 Input Operands
      • 6.47.2.6 Clobbers and Scratch Registers
      • 6.47.2.7 Goto Labels
      • 6.47.2.8 x86 Operand Modifiers
      • 6.47.2.9 x86 Floating-Point asm Operands
    • 6.47.3 Constraints for asm Operands
      • 6.47.3.1 Simple Constraints
      • 6.47.3.2 Multiple Alternative Constraints
      • 6.47.3.3 Constraint Modifier Characters
      • 6.47.3.4 Constraints for Particular Machines
    • 6.47.4 Controlling Names Used in Assembler Code
    • 6.47.5 Variables in Specified Registers
      • 6.47.5.1 Defining Global Register Variables
      • 6.47.5.2 Specifying Registers for Local Variables
    • 6.47.6 Size of an asm
  • 6.48 Alternate Keywords
  • 6.49 Incomplete enum Types
  • 6.50 Function Names as Strings
  • 6.51 Getting the Return or Frame Address of a Function
  • 6.52 Using Vector Instructions through Built-in Functions
  • 6.53 Support for offsetof
  • 6.54 Legacy __sync Built-in Functions for Atomic Memory Access
  • 6.55 Built-in Functions for Memory Model Aware Atomic Operations
  • 6.56 Built-in Functions to Perform Arithmetic with Overflow Checking
  • 6.57 x86-Specific Memory Model Extensions for Transactional Memory
  • 6.58 Object Size Checking Built-in Functions
  • 6.59 Other Built-in Functions Provided by GCC
  • 6.60 Built-in Functions Specific to Particular Target Machines
    • 6.60.1 AArch64 Built-in Functions
    • 6.60.2 Alpha Built-in Functions
    • 6.60.3 Altera Nios II Built-in Functions
    • 6.60.4 ARC Built-in Functions
    • 6.60.5 ARC SIMD Built-in Functions
    • 6.60.6 ARM iWMMXt Built-in Functions
    • 6.60.7 ARM C Language Extensions (ACLE)
    • 6.60.8 ARM Floating Point Status and Control Intrinsics
    • 6.60.9 ARM ARMv8-M Security Extensions
    • 6.60.10 AVR Built-in Functions
    • 6.60.11 Blackfin Built-in Functions
    • 6.60.12 BPF Built-in Functions
    • 6.60.13 BPF Kernel Helpers
    • 6.60.14 FR-V Built-in Functions
      • 6.60.14.1 Argument Types
      • 6.60.14.2 Directly-Mapped Integer Functions
      • 6.60.14.3 Directly-Mapped Media Functions
      • 6.60.14.4 Raw Read/Write Functions
      • 6.60.14.5 Other Built-in Functions
    • 6.60.15 MIPS DSP Built-in Functions
    • 6.60.16 MIPS Paired-Single Support
    • 6.60.17 MIPS Loongson Built-in Functions
      • 6.60.17.1 Paired-Single Arithmetic
      • 6.60.17.2 Paired-Single Built-in Functions
      • 6.60.17.3 MIPS-3D Built-in Functions
    • 6.60.18 MIPS SIMD Architecture (MSA) Support
      • 6.60.18.1 MIPS SIMD Architecture Built-in Functions
    • 6.60.19 Other MIPS Built-in Functions
    • 6.60.20 MSP430 Built-in Functions
    • 6.60.21 NDS32 Built-in Functions
    • 6.60.22 picoChip Built-in Functions
    • 6.60.23 Basic PowerPC Built-in Functions
      • 6.60.23.1 Basic PowerPC Built-in Functions Available on all Configurations
      • 6.60.23.2 Basic PowerPC Built-in Functions Available on ISA 2.05
      • 6.60.23.3 Basic PowerPC Built-in Functions Available on ISA 2.06
      • 6.60.23.4 Basic PowerPC Built-in Functions Available on ISA 2.07
      • 6.60.23.5 Basic PowerPC Built-in Functions Available on ISA 3.0
    • 6.60.24 PowerPC AltiVec/VSX Built-in Functions
      • 6.60.24.1 PowerPC AltiVec Built-in Functions on ISA 2.05
      • 6.60.24.2 PowerPC AltiVec Built-in Functions Available on ISA 2.06
      • 6.60.24.3 PowerPC AltiVec Built-in Functions Available on ISA 2.07
      • 6.60.24.4 PowerPC AltiVec Built-in Functions Available on ISA 3.0
    • 6.60.25 PowerPC Hardware Transactional Memory Built-in Functions
      • 6.60.25.1 PowerPC HTM Low Level Built-in Functions
      • 6.60.25.2 PowerPC HTM High Level Inline Functions
    • 6.60.26 PowerPC Atomic Memory Operation Functions
    • 6.60.27 PowerPC Matrix-Multiply Assist Built-in Functions
    • 6.60.28 RX Built-in Functions
    • 6.60.29 S/390 System z Built-in Functions
    • 6.60.30 SH Built-in Functions
    • 6.60.31 SPARC VIS Built-in Functions
    • 6.60.32 TI C6X Built-in Functions
    • 6.60.33 TILE-Gx Built-in Functions
    • 6.60.34 TILEPro Built-in Functions
    • 6.60.35 x86 Built-in Functions
    • 6.60.36 x86 Transactional Memory Intrinsics
    • 6.60.37 x86 Control-Flow Protection Intrinsics
  • 6.61 Format Checks Specific to Particular Target Machines
    • 6.61.1 Solaris Format Checks
    • 6.61.2 Darwin Format Checks
  • 6.62 Pragmas Accepted by GCC
    • 6.62.1 AArch64 Pragmas
    • 6.62.2 ARM Pragmas
    • 6.62.3 M32C Pragmas
    • 6.62.4 MeP Pragmas
    • 6.62.5 PRU Pragmas
    • 6.62.6 RS/6000 and PowerPC Pragmas
    • 6.62.7 S/390 Pragmas
    • 6.62.8 Darwin Pragmas
    • 6.62.9 Solaris Pragmas
    • 6.62.10 Symbol-Renaming Pragmas
    • 6.62.11 Structure-Layout Pragmas
    • 6.62.12 Weak Pragmas
    • 6.62.13 Diagnostic Pragmas
    • 6.62.14 Visibility Pragmas
    • 6.62.15 Push/Pop Macro Pragmas
    • 6.62.16 Function Specific Option Pragmas
    • 6.62.17 Loop-Specific Pragmas
  • 6.63 Unnamed Structure and Union Fields
  • 6.64 Thread-Local Storage
    • 6.64.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
    • 6.64.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
  • 6.65 Binary Constants using the ‘0b’ Prefix
• 7 Extensions to the C++ Language
  • 7.1 When is a Volatile C++ Object Accessed?
  • 7.2 Restricting Pointer Aliasing
  • 7.3 Vague Linkage
  • 7.4 C++ Interface and Implementation Pragmas
  • 7.5 Where’s the Template?
  • 7.6 Extracting the Function Pointer from a Bound Pointer to Member Function
  • 7.7 C++-Specific Variable, Function, and Type Attributes
  • 7.8 Function Multiversioning
  • 7.9 Type Traits
  • 7.10 C++ Concepts
  • 7.11 Deprecated Features
  • 7.12 Backwards Compatibility
• 8 GNU Objective-C Features
  • 8.1 GNU Objective-C Runtime API
    • 8.1.1 Modern GNU Objective-C Runtime API
    • 8.1.2 Traditional GNU Objective-C Runtime API
  • 8.2 +load: Executing Code before main
    • 8.2.1 What You Can and Cannot Do in +load
  • 8.3 Type Encoding
    • 8.3.1 Legacy Type Encoding
    • 8.3.2 @encode
    • 8.3.3 Method Signatures
  • 8.4 Garbage Collection
  • 8.5 Constant String Objects
  • 8.6 compatibility_alias
  • 8.7 Exceptions
  • 8.8 Synchronization
  • 8.9 Fast Enumeration
    • 8.9.1 Using Fast Enumeration
    • 8.9.2 C99-Like Fast Enumeration Syntax
    • 8.9.3 Fast Enumeration Details
    • 8.9.4 Fast Enumeration Protocol
  • 8.10 Messaging with the GNU Objective-C Runtime
    • 8.10.1 Dynamically Registering Methods
    • 8.10.2 Forwarding Hook
• 9 Binary Compatibility
• 10 gcov—a Test Coverage Program
  • 10.1 Introduction to gcov
  • 10.2 Invoking gcov
  • 10.3 Using gcov with GCC Optimization
  • 10.4 Brief Description of gcov Data Files
  • 10.5 Data File Relocation to Support Cross-Profiling
• 11 gcov-tool—an Offline Gcda Profile Processing Tool
  • 11.1 Introduction to gcov-tool
  • 11.2 Invoking gcov-tool
• 12 gcov-dump—an Offline Gcda and Gcno Profile Dump Tool
  • 12.1 Introduction to gcov-dump
  • 12.2 Invoking gcov-dump
• 13 lto-dump—Tool for dumping LTO object files.
  • 13.1 Introduction to lto-dump
  • 13.2 Invoking lto-dump
• 14 Known Causes of Trouble with GCC
  • 14.1 Actual Bugs We Haven’t Fixed Yet
  • 14.2 Interoperation
  • 14.3 Incompatibilities of GCC
  • 14.4 Fixed Header Files
  • 14.5 Standard Libraries
  • 14.6 Disappointments and Misunderstandings
  • 14.7 Common Misunderstandings with GNU C++
    • 14.7.1 Declare and Define Static Members
    • 14.7.2 Name Lookup, Templates, and Accessing Members of Base Classes
    • 14.7.3 Temporaries May Vanish Before You Expect
    • 14.7.4 Implicit Copy-Assignment for Virtual Bases
  • 14.8 Certain Changes We Don’t Want to Make
  • 14.9 Warning Messages and Error Messages
• 15 Reporting Bugs
  • 15.1 Have You Found a Bug?
  • 15.2 How and Where to Report Bugs
• 16 How To Get Help with GCC
• 17 Contributing to GCC Development
• Funding Free Software
• The GNU Project and GNU/Linux
• GNU General Public License
• GNU Free Documentation License
  • ADDENDUM: How to use this License for your documents
• Contributors to GCC
• Option Index
• Keyword Index

Next: G++ and GCC   [Contents][Index]

Introduction

This manual documents how to use the GNU compilers, as well as their features and incompatibilities, and how to report bugs. It corresponds to the compilers (GCC) version 10.2.0. The internals of the GNU compilers, including how to port them to new targets and some information about how to write front ends for new languages, are documented in a separate manual. See Introduction in GNU Compiler Collection (GCC) Internals.

• G++ and GCC:

  

You can compile C or C++ programs.

• Standards:

  

Language standards supported by GCC.

• Invoking GCC:

  

Command options supported by ‘gcc’.

• C Implementation:

  

How GCC implements the ISO C specification.

• C++ Implementation:

  

How GCC implements the ISO C++ specification.

• C Extensions:

  

GNU extensions to the C language family.

• C++ Extensions:

  

GNU extensions to the C++ language.

• Objective-C:

  

GNU Objective-C runtime features.

• Compatibility:

  

Binary Compatibility

• Gcov:

  

gcov—a test coverage program.

• Gcov-tool:

  

gcov-tool—an offline gcda profile processing program.

• Gcov-dump:

  

gcov-dump—an offline gcda and gcno profile dump tool.

• lto-dump:

  

lto-dump—Tool for dumping LTO object files.

• Trouble:

  

If you have trouble using GCC.

• Bugs:

  

How, why and where to report bugs.

• Service:

  

How To Get Help with GCC

• Contributing:

  

How to contribute to testing and developing GCC.

• Funding:

  

How to help assure funding for free software.

• GNU Project:

  

The GNU Project and GNU/Linux.

• Copying:

  

GNU General Public License says how you can copy and share GCC.

• GNU Free Documentation License:

  

How you can copy and share this manual.

• Contributors:

  

People who have contributed to GCC.

• Option Index:

  

Index to command line options.

• Keyword Index:

  

Index of concepts and symbol names.

Next: G++ and GCC   [Contents][Index]