Red Hat ENTERPRISE LINUX 3 - DEVELOPER TOOLS GUIDE Guide de l'utilisateur télécharger pdf (Page 52)

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Chapter 4. Compiling and Building

The C ABI is considered to be stable, and has been so since at least RHEL3 (again, barring any

incompatibilities mentioned in the above lists). Libraries built on RHEL3 and later can be linked to

objects created on a subsequent environment (RHEL4, RHEL5, and RHEL6).

The C++ ABI is considered to be stable, but less stable than the C ABI, and only as of RHEL4

(corresponding to GCC version 3.4 and above.). As with C, this is only an upward compatibility.

Libraries built on RHEL4 and above can be linked to objects created on a subsequent environment

(RHEL5, and RHEL6).

To force GCC to generate code compatible with the C++ ABI in RHEL releases prior to RHEL4, some

developers have used the -fabi-version=1 option. This practice is not recommended. Objects

created this way are indistinguishable from objects conforming to the current stable ABI, and can be

linked (incorrectly) amongst the different ABIs, especially when using new compilers to generate code

to be linked with old libraries that were built with tools prior to RHEL4.

Warning

The above incompatibilities make it incredibly difficult to maintain ABI shared library sanity

between releases, especially if when developing custom libraries with multiple dependencies

outside of the core libraries. Therefore, if shared libraries are developed, it is highly recommend

that a new version is built for each Red Hat Enterprise Linux release.

4.1.3. Object Compatibility and Interoperability

Two items that are important are the changes and enhancements in the underlying tools used by the

compiler, and the compatibility between the different versions of a language's compiler.

Changes and new features in tools like ld (distributed as part of the binutils package) or in the

dynamic loader (ld.so, distributed as part of the glibc package) can subtly change the object files

that the compiler produces. These changes mean that object files moving to the current release of Red

Hat Enterprise Linux from previous releases may loose functionality, behave differently at runtime, or

otherwise interoperate in a diminished capacity. Known problem areas include:

• ld --build-id

In RHEL6 this is passed to ld by default, whereas RHEL5 ld doesn't recognize it.

• as .cfi_sections support

In RHEL6 this directive allows .debug_frame, .eh_frame or both to be emitted from .cfi*

directives. In RHEL5 only .eh_frame is emitted.

• as, ld, ld.so, and gdb STB_GNU_UNIQUE and %gnu_unique_symbol support

In RHEL6 more debug information is generated and stored in object files. This information relies

on new features detailed in the DWARF standard, and also on new extensions not yet standardized.

In RHEL5, tools like as, ld, gdb, objdump, and readelf may not be prepared for this new

information and may fail to interoperate with objects created with the newer tools. In addition,

RHEL5 produced object files do not support these new features; these object files may be handled

by RHEL6 tools in a sub-optimal manner.

An outgrowth of this enhanced debug information is that the debuginfo packages that ship with

system libraries allow you to do useful source level debugging into system libraries if they are

installed. Refer to Section 5.1, “Installing Debuginfo Packages” for more information on debuginfo

packages.

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