dld.sl.5 (2010 09)

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dld.sl(5)

PA-RISC Systems Only

dld.sl(5)

NAME

dld.sl - dynamic loader

MULTITHREAD USAGE

The dynamic loader is thread-safe.

DESCRIPTION

The

/usr/lib/pa20_64/dld.sl

program is the PA-RISC 64-bit dynamic loader. The

/usr/lib/dld.sl

program is the PA-RISC 32-bit dynamic loader. In programs that use shared

libraries,

dld.sl is invoked automatically at startup time by exec on PA-RISC 64-bit systems and by the

startup ﬁle crt0.o on PA-RISC 32-bit systems. Identical copies of

crt0.o are kept in both

/opt/langtools/lib

and /usr/ccs/lib directories. The dynamic loader is, itself, a shared

library, although it deﬁnes no symbols for use by user programs.

Shared Libraries

Shared libraries are executable ﬁles created with the

-b option to ld (see ld(1)). They must contain

position-independent code (PIC) that can be mapped anywhere in the address space of a process and exe-

cuted with minimal relocation. PIC can use PC-relative addressing modes and/or linkage tables. It is

generated by default by the compilers on PA-RISC 64-bit systems and by specifying the

+z/+Z options on

PA-RISC 32-bit systems.

See the

+help option to ld(1) or the HP-UX Linker and Libraries User’s Guide manual for details on

writing PIC in assembly language.

Incomplete Executables

An executable program linked with one or more shared libraries is called an incomplete executable.

When creating an executable (

a.out) ﬁle from object ﬁles and libraries, the linker does not copy text

(code) or data from the shared library into the output ﬁle. Instead, the dynamic loader maps the library

into the address space of the process at run time. The linker binds all program references to shared

library routines and data to entries in a linkage table, and relies on the dynamic loader to ﬁll in the link-

age table entries once the libraries have been mapped. This linkage table serves as a jump table for func-

tion calls.

Thread local storage is now supported. The dynamic loader will tally each shared library’s thread local

storage size as well as the program’s thread local storage size. When all libraries are loaded on PA-RISC

32-bit systems, the dynamic loader either calls a thread routine to set the thread pointer and allocate

space for the initial thread or calls

mmap() and lwp_setprivate()

to allocate the space and setup

the thread pointer.

On PA-RISC 64-bit systems, the dynamic loader invokes an initializer in the system library

libc which

will do the thread initialization, allocation of the initial thread, and set the thread pointer.

On previous PA-RISC 32-bit releases, shared library data items referenced by the program were copied

into the program executable ﬁle so that the data references could be resolved statically. Beginning with

the Series 700/800 10.0 release, references to shared library data from the

a.out are included in a link-

age table and are resolved at run time.

An incomplete executable contains a list of path names of the shared libraries searched at link time. At

run time, the dynamic loader attaches to the process all shared libraries that were linked with the pro-

gram. The dynamic loader will attempt to load each library from the same directory in which it was

found at link time. It is possible to change the shared library run time search path by specifying a

dynamic path list. See PA-RISC 32-bit Dynamic Path List and/or PA-RISC 64-bit Dynamic Path List .

The text segment of a library is shared among all processes that use it. The data and bss segments are

shared on a page-by-page basis. When a process ﬁrst accesses (reads or writes) a data or bss page, a copy

of that page is made for the process.

PARISC 32-bit Dynamic Path List

There are two was to specify a dynamic path list :

• by storing a directory path list in the executable using the

+b path_list option to ld,

• by linking the executable with

ld option +s, enabling the executable to use the path list deﬁned by

the SHLIB_PATH environment variable at run time.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (8 pages)

PAGE 1
dld.sl(5) dld.sl(5) PA-RISC Systems Only NAME dld.sl - dynamic loader MULTITHREAD USAGE The dynamic loader is thread-safe. DESCRIPTION The /usr/lib/pa20_64/dld.sl program is the PA-RISC 64-bit dynamic loader. The /usr/lib/dld.sl program is the PA-RISC 32-bit dynamic loader. In programs that use shared libraries, dld.sl is invoked automatically at startup time by exec on PA-RISC 64-bit systems and by the startup file crt0.o on PA-RISC 32-bit systems. Identical copies of crt0.
PAGE 2
dld.sl(5) dld.sl(5) PA-RISC Systems Only The path list is a list of one or more path names separated by colons (:). The dynamic path list will work only for libraries specified with the -l or -l: options to ld. However, it can be enabled for libraries specified with a full path name using the -l option to chatr (see chatr (1)). If both +s and +b are used, their relative order on the command line indicates which path list will be searched first in compatibility mode.
PAGE 3
dld.sl(5) PA-RISC Systems Only dld.sl(5) and /usr/ccs/lib/pa20_64. The ancestors of a parent shared library may contain a path_list in rpath, but this is ignored when searching for dependent shared libraries of this parent. Only the parent’s rpath is used. If a library with the same basename (library name without a path) has already been loaded for the program, that library is used to resolve the dependent shared library.
PAGE 4
dld.sl(5) PA-RISC Systems Only dld.sl(5) water mark recorded at link time. When binding symbolic references, the loader chooses the latest version of a symbol that is not later than the high water mark recorded at link time. These two checks help ensure that the version of each library interface used at run time is the same as was expected at link time. Intra-library versioning may be removed in a future release.
PAGE 5
dld.sl(5) dld.sl(5) PA-RISC Systems Only If you do not specify +gst at link time, you can use the +gst flag option of the chatr (1) command to enable the global symbol table mechanism, which causes the loader to build the table and compute the hash values at run time.
PAGE 6
dld.sl(5) dld.sl(5) PA-RISC Systems Only The load order and symbol resolution order may be different in a PA-RISC 32-bit program than in the same PA-RISC 64-bit program because the dynamic loader uses depth-first search order in PA-Risc 32-bit mode and breadth-first search order in PA-RISC 64-bit mode. See Symbol Searching and Dependent Libraries in the +help option to ld(1) or the HP-UX Linker and Libraries User’s Guide for more information.
PAGE 7
dld.sl(5) dld.sl(5) PA-RISC Systems Only /usr/local/lib:/nfs/appserver/lib # path below is ignored: path not starting with ’/’ # and loader will not expand ˜ etc. ~wizkid/lib # second path below ignored: space /user/ipfguru/lib/hpux32: user/ipfguru/lib/hpux64 /net/appserv2/local/lib # ignored:line starting with space /opt/java1.3/jre/lib/PA_RISC2.0/ # java 1.3 PA32 /opt/java1.3/jre/lib/PA_RISC2.0/server # java 1.3 PA32 /opt/java1.3/jre/lib/PA_RISC2.0W/ A # java 1.4 /opt/java1.4/jre/lib/PA_RISC2.
PAGE 8
dld.sl(5) dld.sl(5) PA-RISC Systems Only • Using certain flags or routines described in shl_load (3X). -fbverbose See fastbind (1). -nofastbind See fastbind (1). -load_verbose Display verbose messages concerning possible unsatisfied symbols. This is equivalent to BIND_VERBOSE of shl_load() and RTLD_VERBOSE of dlopen() calls. This option can be used in cases where the application has already been built without either RTLD_VERBOSE or BIND_VERBOSE and verbose messages are expected.