SPRAB89A September   2011  – March 2014

 

  1. 1 Introduction
    1. 1.1  ABIs for the C6000
    2. 1.2  Scope
    3. 1.3  ABI Variants
    4. 1.4  Toolchains and Interoperability
    5. 1.5  Libraries
    6. 1.6  Types of Object Files
    7. 1.7  Segments
    8. 1.8  C6000 Architecture Overview
    9. 1.9  Reference Documents
    10. 1.10 Code Fragment Notation
  2. 2 Data Representation
    1. 2.1 Basic Types
    2. 2.2 Data in Registers
    3. 2.3 Data in Memory
    4. 2.4 Complex Types
    5. 2.5 Structures and Unions
    6. 2.6 Arrays
    7. 2.7 Bit Fields
      1. 2.7.1 Volatile Bit Fields
    8. 2.8 Enumeration Types
  3. 3 Calling Conventions
    1. 3.1 Call and Return
      1. 3.1.1 Return Address Computation
      2. 3.1.2 Call Instructions
      3. 3.1.3 Return Instruction
      4. 3.1.4 Pipeline Conventions
      5. 3.1.5 Weak Functions
    2. 3.2 Register Conventions
    3. 3.3 Argument Passing
    4. 3.4 Return Values
    5. 3.5 Structures and Unions Passed and Returned by Reference
    6. 3.6 Conventions for Compiler Helper Functions
    7. 3.7 Scratch Registers for Inter-Section Calls
    8. 3.8 Setting Up DP
  4. 4 Data Allocation and Addressing
    1. 4.1 Data Sections and Segments
    2. 4.2 Allocation and Addressing of Static Data
      1. 4.2.1 Addressing Methods for Static Data
        1. 4.2.1.1 Near DP-Relative Addressing
        2. 4.2.1.2 Far DP-Relative Addressing
        3. 4.2.1.3 Absolute Addressing
        4. 4.2.1.4 GOT-Indirect Addressing
        5. 4.2.1.5 PC-Relative Addressing
      2. 4.2.2 Placement Conventions for Static Data
        1. 4.2.2.1 Abstract Conventions for Placement
        2. 4.2.2.2 Abstract Conventions for Addressing
        3. 4.2.2.3 Linker Requirements
      3. 4.2.3 Initialization of Static Data
    3. 4.3 Automatic Variables
    4. 4.4 Frame Layout
      1. 4.4.1 Stack Alignment
      2. 4.4.2 Register Save Order
        1. 4.4.2.1 Big-Endian Pair Swapping
        2. 4.4.2.2 Examples
      3. 4.4.3 DATA_MEM_BANK
      4. 4.4.4 C64x+ Specific Stack Layouts
        1. 4.4.4.1 _ _C6000_push_rts Layout
        2. 4.4.4.2 Compact Frame Layout
    5. 4.5 Heap-Allocated Objects
  5. 5 Code Allocation and Addressing
    1. 5.1 Computing the Address of a Code Label
      1. 5.1.1 Absolute Addressing for Code
      2. 5.1.2 PC-Relative Addressing
      3. 5.1.3 PC-Relative Addressing Within the Same Section
      4. 5.1.4 Short-Offset PC-Relative Addressing (C64x)
      5. 5.1.5 GOT-Based Addressing for Code
    2. 5.2 Branching
    3. 5.3 Calls
      1. 5.3.1 Direct PC-Relative Call
      2. 5.3.2 Far Call Trampoline
      3. 5.3.3 Indirect Calls
    4. 5.4 Addressing Compact Instructions
  6. 6 Addressing Model for Dynamic Linking
    1. 6.1 Terms and Concepts
    2. 6.2 Overview of Dynamic Linking Mechanisms
    3. 6.3 DSOs and DLLs
    4. 6.4 Preemption
    5. 6.5 PLT Entries
      1. 6.5.1 Direct Calls to Imported Functions
      2. 6.5.2 PLT Entry Via Absolute Address
      3. 6.5.3 PLT Entry Via GOT
    6. 6.6 The Global Offset Table
      1. 6.6.1 GOT-Based Reference Using Near DP-Relative Addressing
      2. 6.6.2 GOT-Based Reference Using Far DP-Relative Addressing
    7. 6.7 The DSBT Model
      1. 6.7.1 Entry/Exit Sequence for Exported Functions
      2. 6.7.2 Avoiding DP Loads for Internal Functions
      3. 6.7.3 Function Pointers
      4. 6.7.4 Interrupts
      5. 6.7.5 Compatibility With Non-DSBT Code
    8. 6.8 Performance Implications of Dynamic Linking
  7. 7 Thread-Local Storage Allocation and Addressing
    1. 7.1 About Multi-Threading and Thread-Local Storage
    2. 7.2 Terms and Concepts
    3. 7.3 User Interface
    4. 7.4 ELF Object File Representation
    5. 7.5 TLS Access Models
      1. 7.5.1 C6x Linux TLS Models
        1. 7.5.1.1 General Dynamic TLS Access Model
        2. 7.5.1.2 Local Dynamic TLS Access Model
        3. 7.5.1.3 Initial Exec TLS Access Model
          1. 7.5.1.3.1 Thread Pointer
          2. 7.5.1.3.2 Initial Exec TLS Addressing
        4. 7.5.1.4 Local Exec TLS Access Model
      2. 7.5.2 Static Executable TLS Model
        1. 7.5.2.1 Static Executable Addressing
        2. 7.5.2.2 Static Executable TLS Runtime Architecture
        3. 7.5.2.3 Static Executable TLS Allocation
          1. 7.5.2.3.1 TLS Initialization Image Allocation
          2. 7.5.2.3.2 Main Thread’s TLS Allocation
          3. 7.5.2.3.3 Thread Library’s TLS Region Allocation
        4. 7.5.2.4 Static Executable TLS Initialization
          1. 7.5.2.4.1 Main Thread’s TLS Initialization
          2. 7.5.2.4.2 TLS Initialization by Thread Library
        5. 7.5.2.5 Thread Pointer
      3. 7.5.3 Bare-Metal Dynamic Linking TLS Model
        1. 7.5.3.1 Default TLS Addressing for Bare-Metal Dynamic Linking
        2. 7.5.3.2 TLS Block Creation
    6. 7.6 Thread-Local Symbol Resolution and Weak References
      1. 7.6.1 General and Local Dynamic TLS Weak Reference Addressing
      2. 7.6.2 Initial and Local Executable TLS Weak Reference Addressing
      3. 7.6.3 Static Exec and Bare Metal Dynamic TLS Model Weak References
  8. 8 Helper Function API
    1. 8.1 Floating-Point Behavior
    2. 8.2 C Helper Function API
    3. 8.3 Special Register Conventions for Helper Functions
    4. 8.4 Helper Functions for Complex Types
    5. 8.5 Floating-Point Helper Functions for C99
  9. 9 Standard C Library API
    1. 9.1  Reserved Symbols
    2. 9.2  <assert.h> Implementation
    3. 9.3  <complex.h> Implementation
    4. 9.4  <ctype.h> Implementation
    5. 9.5  <errno.h> Implementation
    6. 9.6  <float.h> Implementation
    7. 9.7  <inttypes.h> Implementation
    8. 9.8  <iso646.h> Implementation
    9. 9.9  <limits.h> Implementation
    10. 9.10 <locale.h> Implementation
    11. 9.11 <math.h> Implementation
    12. 9.12 <setjmp.h> Implementation
    13. 9.13 <signal.h> Implementation
    14. 9.14 <stdarg.h> Implementation
    15. 9.15 <stdbool.h> Implementation
    16. 9.16 <stddef.h> Implementation
    17. 9.17 <stdint.h> Implementation
    18. 9.18 <stdio.h> Implementation
    19. 9.19 <stdlib.h> Implementation
    20. 9.20 <string.h> Implementation
    21. 9.21 <tgmath.h> Implementation
    22. 9.22 <time.h> Implementation
    23. 9.23 <wchar.h> Implementation
    24. 9.24 <wctype.h> Implementation
  10. 10C++ ABI
    1. 10.1  Limits (GC++ABI 1.2)
    2. 10.2  Export Template (GC++ABI 1.4.2)
    3. 10.3  Data Layout (GC++ABI Chapter 2)
    4. 10.4  Initialization Guard Variables (GC++ABI 2.8)
    5. 10.5  Constructor Return Value (GC++ABI 3.1.5)
    6. 10.6  One-Time Construction API (GC++ABI 3.3.2)
    7. 10.7  Controlling Object Construction Order (GC++ ABI 3.3.4)
    8. 10.8  Demangler API (GC++ABI 3.4)
    9. 10.9  Static Data (GC++ ABI 5.2.2)
    10. 10.10 Virtual Tables and the Key function (GC++ABI 5.2.3)
    11. 10.11 Unwind Table Location (GC++ABI 5.3)
  11. 11Exception Handling
    1. 11.1  Overview
    2. 11.2  PREL31 Encoding
    3. 11.3  The Exception Index Table (EXIDX)
      1. 11.3.1 Pointer to Out-of-Line EXTAB Entry
      2. 11.3.2 EXIDX_CANTUNWIND
      3. 11.3.3 Inlined EXTAB Entry
    4. 11.4  The Exception Handling Instruction Table (EXTAB)
      1. 11.4.1 EXTAB Generic Model
      2. 11.4.2 EXTAB Compact Model
      3. 11.4.3 Personality Routines
    5. 11.5  Unwinding Instructions
      1. 11.5.1 Common Sequence
      2. 11.5.2 Byte-Encoded Unwinding Instructions
      3. 11.5.3 24-Bit Unwinding Encoding
    6. 11.6  Descriptors
      1. 11.6.1 Encoding of Type Identifiers
      2. 11.6.2 Scope
      3. 11.6.3 Cleanup Descriptor
      4. 11.6.4 Catch Descriptor
      5. 11.6.5 Function Exception Specification (FESPEC) Descriptor
    7. 11.7  Special Sections
    8. 11.8  Interaction With Non-C++ Code
      1. 11.8.1 Automatic EXIDX Entry Generation
      2. 11.8.2 Hand-Coded Assembly Functions
    9. 11.9  Interaction With System Features
      1. 11.9.1 Shared Libraries
      2. 11.9.2 Overlays
      3. 11.9.3 Interrupts
    10. 11.10 Assembly Language Operators in the TI Toolchain
  12. 12DWARF
    1. 12.1 DWARF Register Names
    2. 12.2 Call Frame Information
    3. 12.3 Vendor Names
    4. 12.4 Vendor Extensions
  13. 13ELF Object Files (Processor Supplement)
    1. 13.1 Registered Vendor Names
    2. 13.2 ELF Header
    3. 13.3 Sections
      1. 13.3.1 Section Indexes
      2. 13.3.2 Section Types
      3. 13.3.3 Extended Section Header Attributes
      4. 13.3.4 Subsections
      5. 13.3.5 Special Sections
      6. 13.3.6 Section Alignment
    4. 13.4 Symbol Table
      1. 13.4.1 Symbol Types
      2. 13.4.2 Common Block Symbols
      3. 13.4.3 Symbol Names
      4. 13.4.4 Reserved Symbol Names
      5. 13.4.5 Mapping Symbols
    5. 13.5 Relocation
      1. 13.5.1 Relocation Types
      2. 13.5.2 Relocation Operations
      3. 13.5.3 Relocation of Unresolved Weak References
  14. 14ELF Program Loading and Dynamic Linking (Processor Supplement)
    1. 14.1 Program Header
      1. 14.1.1 Base Address
      2. 14.1.2 Segment Contents
      3. 14.1.3 Bound and Read-Only Segments
      4. 14.1.4 Thread-Local Storage
    2. 14.2 Program Loading
    3. 14.3 Dynamic Linking
      1. 14.3.1 Program Interpreter
      2. 14.3.2 Dynamic Section
      3. 14.3.3 Shared Object Dependencies
      4. 14.3.4 Global Offset Table
      5. 14.3.5 Procedure Linkage Table
      6. 14.3.6 Preemption
      7. 14.3.7 Initialization and Termination
    4. 14.4 Bare-Metal Dynamic Linking Model
      1. 14.4.1 File Types
      2. 14.4.2 ELF Identification
      3. 14.4.3 Visibility and Binding
      4. 14.4.4 Data Addressing
      5. 14.4.5 Code Addressing
      6. 14.4.6 Dynamic Information
  15. 15Linux ABI
    1. 15.1  File Types
    2. 15.2  ELF Identification
    3. 15.3  Program Headers and Segments
    4. 15.4  Data Addressing
      1. 15.4.1 Data Segment Base Table (DSBT)
      2. 15.4.2 Global Offset Table (GOT)
    5. 15.5  Code Addressing
    6. 15.6  Lazy Binding
    7. 15.7  Visibility
    8. 15.8  Preemption
    9. 15.9  Import-as-Own Preemption
    10. 15.10 Program Loading
    11. 15.11 Dynamic Information
    12. 15.12 Initialization and Termination Functions
    13. 15.13 Summary of the Linux Model
  16. 16Symbol Versioning
    1. 16.1 ELF Symbol Versioning Overview
    2. 16.2 Version Section Identification
  17. 17Build Attributes
    1. 17.1 C6000 ABI Build Attribute Subsection
    2. 17.2 C6000 Build Attribute Tags
  18. 18Copy Tables and Variable Initialization
    1. 18.1 Copy Table Format
    2. 18.2 Compressed Data Formats
      1. 18.2.1 RLE
      2. 18.2.2 LZSS Format
    3. 18.3 Variable Initialization
  19. 19Extended Program Header Attributes
    1. 19.1 Encoding
    2. 19.2 Attribute Tag Definitions
    3. 19.3 Extended Program Header Attributes Section Format
  20. 20Revision History

13.3.5 Special Sections

The System V ABI, along with other base documents and other sections of this ABI, defines several sections with dedicated purposes. Table 13-4 consolidates dedicated sections used by the C6000 and groups them by functionality.

Section names are not mandated by the ABI. Special sections should be identified by type, not by name. However, interoperability among toolchains can be improved by following these conventions. For example, using these names may decrease the likelihood of having to write custom linker commands to link relocatable files built by different compilers.

The ABI does mandate that a section whose name does match an entry in the table must be used for the specified purpose. For example, the compiler is not required to generate code into a section called .text, but it is not allowed to generate a section called .text containing anything other than code.

All of the section names listed in the table that follows are prefixes. The type and attributes apply to all sections with names that begin with these strings.

Table 13-4 C6000 Special Sections
PrefixTypeAttributes
Code Sections
.textSHT_PROGBITSSHF_ALLOC + SHF_EXECINSTR
.pltSHT_PROGBITSSHF_ALLOC + SHF_EXECINSTR
Near Data Sections
.bssSHT_NOBITSSHF_ALLOC + SHF_WRITE
.neardataSHT_PROGBITSSHF_ALLOC + SHF_WRITE
.rodataSHT_PROGBITSSHF_ALLOC
Far Data Sections
.farSHT_NOBITSSHF_ALLOC + SHF_WRITE
.fardataSHT_PROGBITSSHF_ALLOC + SHF_WRITE
.constSHT_PROGBITSSHF_ALLOC
.fardata:constSHT_PROGBITSSHF_ALLOC
Dynamic Data Sections
.gotSHT_PROGBITSSHF_ALLOC + SHF_WRITE
.dsbtSHT_PROGBITSSHF_ALLOC + SHF_WRITE
Exception Handling Data Sections
.C6000.exidxSHT_C6000_UNWINDSHF_ALLOC + SHF_LINK_ORDER
.C6000.extabSHT_PROGBITSSHF_ALLOC
Initialization and Termination Sections
.initSHT_PROGBITSSHF_ALLOC + SHF_EXECINSTR
.finiSHT_PROGBITSSHF_ALLOC + SHF_EXECINSTR
.preinit_arraySHT_PREINIT_ARRAYSHF_ALLOC + SHF_WRITE
.init_arraySHT_INIT_ARRAYSHF_ALLOC + SHF_WRITE
.fini_arraySHT_FINI_ARRAYSHF_ALLOC + SHF_WRITE
ELF Structures
.relSHT_RELNone
.relaSHT_RELANone
.symtabSHT_SYMTABNone
.symtab_shndxSHT_SYMTAB_SHNDXNone
.strtabSHT_STRTABSHF_STRINGS
.shstrtabSHT_STRTABSHF_STRINGS
.noteSHT_NOTENone
Dynamic Loading Structure
.dynamic (1)SHT_DYNAMICSHF_ALLOC
.dynsym (1)SHT_DYNSYMSHF_ALLOC
.dynstr (1)SHT_STRTABSHF_ALLOC + SHF_STRINGS
.hash (1)SHT_TABSHF_ALLOC
.interpSHT_PROGBITSNone
Build Attributes
.C6000.attributesSHT_C6000_ATTRIBUTESNone
Symbolic Debug Sections
.debug (2)SHT_PROGBITSNone
Symbol Versioning Sections(1)
.gnu.versionSHT_GNU_versymSHF_ALLOC
.gnu.version_dSHT_GNU_verdefSHF_ALLOC
.gnu.version_rSHT_GNU_verneedSHF_ALLOC
Sections for Thread-Local Storage
.tbssSHT_NOBITSSHF_ALLOC + SHF_WRITE + SHF_TLS
.tdataSHT_PROGBITSSHF_ALLOC + SHF_WRITE + SHF_TLS
.tdata1SHT_PROGBITSSHF_ALLOC + SHF_WRITE + SHF_TLS
.TI.tls_initSHT_PROGBITSSHF_ALLOC
TI Toolchain-Specific Sections
.stackSHT_NOBITSSHF_ALLOC + SHF_WRITE
.sysmemSHT_NOBITSSHF_ALLOC + SHF_WRITE
.cioSHT_NOBITSSHF_ALLOC + SHF_WRITE
.switchSHT_PROGBITSSHF_ALLOC
.binitSHT_PROGBITSSHF_ALLOC
.cinitSHT_TI_INITINFOSHF_ALLOC
.const:handler_tableSHT_PROGBITSSHF_ALLOC
.ovlySHT_PROGBITSSHF_ALLOC
.ppdataSHT_NOBITSSHF_ALLOC + SHF_WRITE
.ppinfoSHT_NOBITSSHF_ALLOC + SHF_WRITE
.TI.crctabSHT_PROGBITSSHF_ALLOC
.TI.icodeSHT_TI_ICODENone
.TI.phattrsSHT_TI_PHATTRSNone
.TI.preempt.mapSHT_C6000_PREEMPTMAPSHF_ALLOC
.TI.xrefSHT_TI_XREFNone
.TI.section.flagsSHT_TI_SH_FLAGSNone
.TI.symbol.aliasSHT_TI_SYMALIASNone
.TI.section.pageSHT_TI_SH_PAGENone
Sections in the System V ABI but Unused by the C6000 EABI
.comment
.data
.data1
.line
.rodata1
(1) Whether the .dynamic section and related sections are allocated into memory is platform specific.
(2) Additional sections with names like .debug_info and .debug_line are also used. The .debug section name is a prefix, as are other section names. The type and attributes apply to all sections with names that begin with .debug.

The "TI Toolchain-Specific Sections" sections in the previous table are used by the TI toolchain in various toolchain-specific ways. The ABI does not mandate the use of these sections (although interoperability encourages their use), but it does reserve these names.

The "Sections in the System V ABI but Unused by the C6000 EABI" sections in the previous table are specified by the System V ABI, but are not used or defined under the C6000 ABI. Other sections are used by TI for other devices; these names are reserved.

See Chapter 7 for details about thread-local storage.

In addition, .common and .scommon are section names used by the linker. These are abstract sections, not actual sections in the object files. The names are a convention in the linker command file for placing variables. These sections should not be used for other purposes.