There are several changes to the link editor, ld(1), in this release. The most important change is its ability to handle the new ELF native file format.
The recommended method for building libraries and executables is through the compiler driver rather than by invoking the linker directly. The compiler automatically supplies several files needed by the linker.
You cannot mix libraries--32-bit programs must link with 32-bit libraries and 64-bit programs must link with 64-bit libraries. ELF32 objects link with other ELF32 objects and ELF64 objects link with other ELF64 objects.
Some options have been renamed in the new linker, some have remained the same, and others are no longer needed. Table 15-1 compares the SunOS release 4 ld command to the Solaris 7 ld command.
The sections following Table 15-1 explain how certain linking tasks are affected by the option differences.
Table 15-1 Comparison of ld Options
SunOS release 4 Option |
Solaris 7 Replacement |
Notes |
---|---|---|
-align datum |
-M mapfile |
Uses mapfile and distinct sections |
-assert definitions |
Default |
|
-assert nodefinitions |
-znodefs |
Issues a fatal error instead of a warning |
-assert nosymbolic |
-zdefs |
Issues a fatal error instead of a warning |
-assert pure-text |
-ztext |
Issues a fatal error instead of a warning |
-A name |
No replacement |
dlopen(3X) and dlclose(3X) can approximate this behavior |
-Bdynamic |
-Bdynamic |
Applies only to the inclusion of shared libraries; use -dy (the default) to build dynamically linked executables. See "Building Executables". |
-Bnosymbolic |
-zdefs |
|
-Bstatic |
-dn & -Bstatic |
The -dn option must be specified to completely eliminate the dynamic linker. Use -Bstatic in dynamic mode to include archive libraries. (Used as a toggle. See "Building Executables".) |
-Bsymbolic |
-Bsymbolic |
Also gets -assert nosymbolic with this option |
-d -dc -dp |
Default |
Use -b option in SVR4 to turn off |
-D hex |
-M mapfile |
mapfile contains different mechanisms to accomplish desired effect |
-e entry |
-e entry |
|
no -e |
-G |
Creates a shared object |
-lx[.v] |
-lx |
Only major number versioning of shared libraries is currently supported |
-Ldir |
-Ldir |
dir not recorded in executable; use -R option instead. |
-M |
-m |
|
-n |
Default |
SVR4 executable format compresses disk image as -n |
-N |
No replacement |
|
-o name |
-o name |
|
-p |
Default |
Can override with -M mapfile |
-r |
-r |
|
-S |
No replacement |
|
-s |
-s |
|
-t |
No replacement |
|
-T hex |
-M mapfile |
mapfile contains different mechanisms to accomplish desired effect |
-Tdata hex |
-M mapfile |
mapfile contains different mechanisms to accomplish desired effect |
-u name |
-u name |
|
-x |
No replacement |
|
-X |
No replacement |
|
-y sym |
No replacement |
|
-z |
Default |
The procedure for building shared libraries in the Solaris 7 operating environment requires the -G option. In the SunOS release 4 software, the linker infers that a shared library is being built if the -e option is absent. As shared libraries may have entry points, this option can no longer be used.
The -Bdynamic and -Bstatic options are still available, but their behavior is different. These options now refer to library inclusions to the executable rather than to the binding. Executable binding is set exclusively with the new -dy and -dn options in the Solaris 7 software. The -dy option is the default. It is required to create a dynamically linked executable. The -dn option is required to create a statically linked executable.
The -Bdynamic and -Bstatic options apply only when using the -dy option. -Bdynamic tells the link editor to include shared libraries, while -Bstatic tells it to include archive libraries. These options act as a toggle governing subsequent -l arguments until the next -Bdynamic or -Bstatic option is encountered.
The following examples show SunOS release 4 and Solaris 7 commands that can be used to create similar executables.
sunos4.1% ld -Bstatic test.o -lx
Uses libx.a and creates a static executable
sunos5.x% cc -dn test.o -lx
Uses libx.a and creates a static executable
sunos4.1% ld -Bdynamic test.o -lx
Uses libx.so and creates a dynamic executable
sunos5.x% cc test.o -lx
Uses libx.so and creates a dynamic executable
sunos4.1% ld -Bdynamic test.o -Bstatic -lx
Uses libx.a and creates a dynamic executable
sunos5.x% cc test.o -Bstatic -lx
Uses libx.a and creates a dynamic executable
In the SunOS release 4 software, directories specified with the -L option were searched at link time and the information retained for use at execution time. This behavior is now divided between the -L and -R options. The -L option specifies the directories to search at link time; the -R option tells the linker the search paths to be retained for use at run time. See "Search Path Rules", in the next section for more information.
As with the -Bdynamic and -Bstatic options, the position of the -L option has significance; it applies only to the subsequent -l options.
The dynamic linker and the runtime linker determine their search paths through a different algorithm from that used by the SunOS release 4 linker.
The examples below compare the search paths for the dynamic linker and the runtime linker for SunOS release 4 and the Solaris 7 operating environment. Notice that in the latter, the search path for the link editor and the runtime linker are affected by the LD_LIBRARY_PATH
setting. However, the runtime linker permits programs to find shared libraries without having to set LD_LIBRARY_PATH
and makes the loading of shared libraries even more efficient. In Solaris 7, use $ORIGIN instead, since you must build your program with a built-in library path relative to where prog is installed. For example .../package/bin/prog uses .../package/lib/libmine.so.1.
SunOS release 4 linker search paths:
Link Editor: -L, LD_LIBRARY_PATH
, /usr/lib, /usr/local/lib
Runtime Linker: LD_LIBRARY_PATH
, -L, /usr/lib, /usr/local/lib
Solaris 7 linker search paths (with LD_LIBRARY_PATH
=dirlist1):
Link Editor: -L, dirlist1, /usr/ccs/lib, /usr/lib
Runtime Linker: dirlist1, -R, /usr/lib
Solaris 7 linker search paths (with LD_LIBRARY_PATH
=dirlist1,dirlist2):
Link Editor: dirlist1, -L, dirlist2, /usr/ccs/lib, /usr/lib
Solaris 7 linker search paths using $ORIGIN
Runtime Linker: -R, $ORIGIN/../lib
Also, with Solaris 7, LD_LIBRARY_PATH_64
is a 64-bit only version of LD_LIBRARY_PATH
.
The SunOS release 4 software supported both major and minor version numbers on shared libraries. The Solaris 7 operating environment supports only the major version number. For binary compatibility support, major and minor version numbers are recognized on SunOS release 4 shared libraries. These libraries are required to retain the SunOS release 4 major and minor version numbers.
Table 15-2 shows versions of SunOS release 4 and Solaris 7 shared libraries.
Table 15-2 Example Shared Libraries
SunOS release 4 |
Solaris 7 |
---|---|
libc.so.1.7 |
libc.so.1 |
libdl.so.1.0 |
libdl.so.1 |
In SunOS release 4 system software, when the -l option was specified, the build environment linker searched for a library with both major and minor numbers. For example, if -ldl was specified, the library, libdl.so.1.0 was linked. In the Solaris 7 environment, even though major numbers are still supported, the default behavior of the link editor is to ignore version numbers. Using the previous example, the build environment link editor now searches for libdl.so and a symbolic link points to a specific version file.
The recording of a dependency in a dynamic executable or shared object is, by default, the file name of the associated shared object as it is referenced by the link editor. To provide a more consistent means of specifying dependencies, shared objects can record within themselves the file name by which they should be referenced at runtime. This is specified with the -h option when linking the library file.
Symbolic links have been created for most libraries in this release. You should build any new shared libraries with major numbers, then create a symbolic link to the version of the library that is used most often.
A new utility, dump(1), makes it easier to debug object files or to check the static and dynamic linking, see "Backing Up and Restoring Files"). The dump -L option displays the information needed by the runtime linker that is contained in the executable. This information is contained in the dynamic section of an ELF file. The RPATH
entry displays search paths specified by the -R option to ld.
The following example:
Creates a link from libx.so.1 to libx.so
Shows dump output, including the SONAME
field, which stores the information passed with the -h option.
examples% cc -G -o libx.so.1 -h libx.so.1 libx.o examples% cp libx.so.1 /mylibs examples% ln -s /mylibs/libx.so.1 /mylibs/libx.so examples% dump -Lv libx.so.1 libx.so.1: **** DYNAMIC SECTION INFORMATION **** .dynamic : [INDEX] Tag Value [1] INIT 0x3b8 [2] FINI 0x3f4 [3] SONAME libx.so.1 [4] HASH 0x94 [5] STRTAB 0x33c [6] SYMTAB 0x14c [7] STRSZ 0x62 [8] SYMENT 0x10 [9] PLTGOT 0x10404 [10] PLTSZ 0xc [11] PLTREL 0x7 [12] JMPREL 0x3ac [13] RELA 0x3a0 [14] RELASZ 0x18 [15] RELAENT 0xc |
If a library needs other dynamic libraries, they should be specified along with an RPATH
, as the next example shows.
The next example compiles prog.c, dynamically linking libx.so (as built in the previous example), and specifies that the binary retain the current directory information for execution. This example shows the output of dump from the compiled program, prog.c. Here, the information stored in the SONAME
field of the previous example is shown as NEEDED
by prog. When prog is run, it will use libx.so.1 even if libx.so is linked to a different version.
examples% cc -o prog prog.c -L/mylibs -R/mylibs -lx example% dump -Lv prog prog: **** DYNAMIC SECTION INFORMATION **** .dynamic : [INDEX] Tag Value [1] NEEDED libx.so.1 [2] NEEDED libc.so.1 [3] INIT 0x1b1ac [4] FINI 0x1b248 [5] RPATH /mylibs [6] HASH 0x100e8 [7] STRTAB 0x17f90 [8] SYMTAB 0x12be0 [9] STRSZ 0x31e1 [10] SYMENT 0x10 [11] DEBUG 0x0 [12] PLTGOT 0x2b25c [13] PLTSZ 0x30 [14] PLTREL 0x7 [15] JMPREL 0x1b180 [16] RELA 0x1b174 [17] RELASZ 0x3c [18] RELAENT 0xc |