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Oracle Solaris 11.1 Linkers and Libraries Guide     Oracle Solaris 11.1 Information Library
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Document Information

Preface

Part I Using the Link-Editor and Runtime Linker

1.  Introduction to the Oracle Solaris Link Editors

2.  Link-Editor

3.  Runtime Linker

4.  Shared Objects

Part II Quick Reference

5.  Link-Editor Quick Reference

Part III Advanced Topics

6.  Direct Bindings

7.  Building Objects to Optimize System Performance

8.  Mapfiles

9.  Interfaces and Versioning

10.  Establishing Dependencies with Dynamic String Tokens

11.  Extensibility Mechanisms

Part IV ELF Application Binary Interface

12.  Object File Format

File Format

Data Representation

ELF Header

ELF Identification

Data Encoding

Sections

Section Merging

Special Sections

Ancillary Section

COMDAT Section

Group Section

Capabilities Section

Hash Table Section

Move Section

Note Section

Relocation Sections

Relocation Calculations

SPARC: Relocations

SPARC: Relocation Types

64-bit SPARC: Relocation Types

x86: Relocations

32-bit x86: Relocation Types

x64: Relocation Types

String Table Section

Symbol Table Section

Symbol Values

Symbol Table Layout and Conventions

Symbol Sort Sections

Register Symbols

Syminfo Table Section

Versioning Sections

Version Definition Section

Version Dependency Section

Version Symbol Section

13.  Program Loading and Dynamic Linking

14.  Thread-Local Storage

Part V Appendices

A.  Linker and Libraries Updates and New Features

B.  System V Release 4 (Version 1) Mapfiles

Index

Versioning Sections

Objects created by the link-editor can contain two types of versioning information.

The structures that form these sections are defined in sys/link.h. Sections that contain versioning information are named .SUNW_version.

Version Definition Section

This section is defined by the type SHT_SUNW_verdef. If this section exists, a SHT_SUNW_versym section must also exist. These two structures provide an association of symbols to version definitions within the file. See Creating a Version Definition. Elements of this section have the following structure.

typedef struct {
        Elf32_Half      vd_version;
        Elf32_Half      vd_flags;
        Elf32_Half      vd_ndx;
        Elf32_Half      vd_cnt;
        Elf32_Word      vd_hash;
        Elf32_Word      vd_aux;
        Elf32_Word      vd_next;
} Elf32_Verdef;
 
typedef struct {
        Elf32_Word      vda_name;
        Elf32_Word      vda_next;
} Elf32_Verdaux;

typedef struct {
        Elf64_Half      vd_version;
        Elf64_Half      vd_flags;
        Elf64_Half      vd_ndx;
        Elf64_Half      vd_cnt;
        Elf64_Word      vd_hash;
        Elf64_Word      vd_aux;
        Elf64_Word      vd_next;
} Elf64_Verdef;
 
typedef struct {
        Elf64_Word      vda_name;
        Elf64_Word      vda_next;
} Elf64_Verdaux;
vd_version

This member identifies the version of the structure, as listed in the following table.

Name
Value
Meaning
VER_DEF_NONE
0
Invalid version.
VER_DEF_CURRENT
>=1
Current version.

The value 1 signifies the original section format. Extensions require new versions with higher numbers. The value of VER_DEF_CURRENT changes as necessary to reflect the current version number.

vd_flags

This member holds version definition-specific information, as listed in the following table.

Name
Value
Meaning
VER_FLG_BASE
0x1
Version definition of the file.
VER_FLG_WEAK
0x2
Weak version identifier.

The base version definition is always present when version definitions, or symbol auto-reduction, have been applied to the file. The base version provides a default version for the files reserved symbols. A weak version definition has no symbols associated with the version. See Creating a Weak Version Definition.

vd_ndx

The version index. Each version definition has a unique index that is used to associate SHT_SUNW_versym entries to the appropriate version definition.

vd_cnt

The number of elements in the Elf32_Verdaux array.

vd_hash

The hash value of the version definition name. This value is generated using the same hashing function that is described in Hash Table Section.

vd_aux

The byte offset from the start of this Elf32_Verdef entry to the Elf32_Verdaux array of version definition names. The first element of the array must exist. This element points to the version definition string this structure defines. Additional elements can be present. The number of elements is indicated by the vd_cnt value. These elements represent the dependencies of this version definition. Each of these dependencies will have its own version definition structure.

vd_next

The byte offset from the start of this Elf32_Verdef structure to the next Elf32_Verdef entry.

vda_name

The string table offset to a null-terminated string, giving the name of the version definition.

vda_next

The byte offset from the start of this Elf32_Verdaux entry to the next Elf32_Verdaux entry.

Version Dependency Section

The version dependency section is defined by the type SHT_SUNW_verneed. This section complements the dynamic dependency requirements of the file by indicating the version definitions required from these dependencies. A recording is made in this section only if a dependency contains version definitions. Elements of this section have the following structure.

typedef struct {
        Elf32_Half      vn_version;
        Elf32_Half      vn_cnt;
        Elf32_Word      vn_file;
        Elf32_Word      vn_aux;
        Elf32_Word      vn_next;
} Elf32_Verneed;
 
typedef struct {
        Elf32_Word      vna_hash;
        Elf32_Half      vna_flags;
        Elf32_Half      vna_other;
        Elf32_Word      vna_name;
        Elf32_Word      vna_next;
} Elf32_Vernaux;

typedef struct {
        Elf64_Half      vn_version;
        Elf64_Half      vn_cnt;
        Elf64_Word      vn_file;
        Elf64_Word      vn_aux;
        Elf64_Word      vn_next;
} Elf64_Verneed;
 
typedef struct {
        Elf64_Word      vna_hash;
        Elf64_Half      vna_flags;
        Elf64_Half      vna_other;
        Elf64_Word      vna_name;
        Elf64_Word      vna_next;
} Elf64_Vernaux;
vn_version

This member identifies the version of the structure, as listed in the following table.

Name
Value
Meaning
VER_NEED_NONE
0
Invalid version.
VER_NEED_CURRENT
>=1
Current version.

The value 1 signifies the original section format. Extensions require new versions with higher numbers. The value of VER_NEED_CURRENT changes as necessary to reflect the current version number.

vn_cnt

The number of elements in the Elf32_Vernaux array.

vn_file

The string table offset to a null-terminated string, providing the file name of a version dependency. This name matches one of the .dynamic dependencies found in the file. See Dynamic Section.

vn_aux

The byte offset, from the start of this Elf32_Verneed entry, to the Elf32_Vernaux array of version definitions that are required from the associated file dependency. At least one version dependency must exist. Additional version dependencies can be present, the number being indicated by the vn_cnt value.

vn_next

The byte offset, from the start of this Elf32_Verneed entry, to the next Elf32_Verneed entry.

vna_hash

The hash value of the version dependency name. This value is generated using the same hashing function that is described in Hash Table Section.

vna_flags

Version dependency specific information, as listed in the following table.

Name
Value
Meaning
VER_FLG_WEAK
0x2
Weak version identifier.
VER_FLG_INFO
0x4
SHT_SUNW_versym reference exists for informational purposes, and need not be validated at runtime.

A weak version dependency indicates an original binding to a weak version definition.

vna_other

If non-zero, the version index assigned to this dependency version. This index is used within the SHT_SUNW_versym to assign global symbol references to this version.

Versions of Solaris up to and including the Oracle Solaris 10 release, did not assign version symbol indexes to dependency versions. In these objects, the value of vna_other is 0.

vna_name

The string table offset to a null-terminated string, giving the name of the version dependency.

vna_next

The byte offset from the start of this Elf32_Vernaux entry to the next Elf32_Vernaux entry.

Version Symbol Section

The version symbol section is defined by the type SHT_SUNW_versym. This section consists of an array of elements of the following structure.

typedef Elf32_Half      Elf32_Versym;
typedef Elf64_Half      Elf64_Versym;

The number of elements of the array must equal the number of symbol table entries that are contained in the associated symbol table. This number is determined by the section's sh_link value. Each element of the array contains a single index that can have the values shown in the following table.

Table 12-25 ELF Version Dependency Indexes

Name
Value
Meaning
VER_NDX_LOCAL
0
Symbol has local scope.
VER_NDX_GLOBAL
1
Symbol has global scope and is assigned to the base version definition.
>1
Symbol has global scope and is assigned to a user-defined version definition, SHT_SUNW_verdef, or a version dependency, SHT_SUNW_verneed.

A symbol may be assigned the special reserved index 0. This index can be assigned for any of the following reasons.

Versions defined by an object are assigned version indexes starting at 1 and incremented by 1 for each version. Index 1 is reserved for the first global version. If the object does not have a SHT_SUNW_verdef version definition section, then all the global symbols defined by the object receive index 1. If the object does have a version definition section, then VER_NDX_GLOBAL simply refers to the first such version.

Versions required by the object from other SHT_SUNW_verneed dependencies, are assigned version indexes that start 1 past the final version definition index. These indexes are also incremented by 1 for each version. Since index 1 is always reserved for VER_NDX_GLOBAL, the first possible index for a dependency version is 2.

Versions of Solaris up to and including the Oracle Solaris 10 release, did not assign a version index to a SHT_SUNW_verneed dependency version. In such an object, any symbol reference had a version index of 0 indicating that no versioning information is available for that symbol.