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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-24 04:52:22 +0000
commit3d08cd331c1adcf0d917392f7e527b3f00511748 (patch)
tree312f0d1e1632f48862f044b8bb87e602dcffb5f9 /man3/dlsym.3
parentAdding debian version 6.7-2. (diff)
downloadmanpages-3d08cd331c1adcf0d917392f7e527b3f00511748.tar.xz
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Merging upstream version 6.8.
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-'\" t
-.\" Copyright 1995 Yggdrasil Computing, Incorporated.
-.\" and Copyright 2003, 2015 Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" SPDX-License-Identifier: GPL-2.0-or-later
-.\"
-.TH dlsym 3 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-dlsym, dlvsym \- obtain address of a symbol in a shared object or executable
-.SH LIBRARY
-Dynamic linking library
-.RI ( libdl ", " \-ldl )
-.SH SYNOPSIS
-.nf
-.B #include <dlfcn.h>
-.P
-.BI "void *dlsym(void *restrict " handle ", const char *restrict " symbol );
-.P
-.B #define _GNU_SOURCE
-.B #include <dlfcn.h>
-.P
-.BI "void *dlvsym(void *restrict " handle ", const char *restrict " symbol ,
-.BI " const char *restrict " version );
-.fi
-.SH DESCRIPTION
-The function
-.BR dlsym ()
-takes a "handle" of a dynamic loaded shared object returned by
-.BR dlopen (3)
-along with a null-terminated symbol name,
-and returns the address where that symbol is
-loaded into memory.
-If the symbol is not found, in the specified
-object or any of the shared objects that were automatically loaded by
-.BR dlopen (3)
-when that object was loaded,
-.BR dlsym ()
-returns NULL.
-(The search performed by
-.BR dlsym ()
-is breadth first through the dependency tree of these shared objects.)
-.P
-In unusual cases (see NOTES) the value of the symbol could actually be NULL.
-Therefore, a NULL return from
-.BR dlsym ()
-need not indicate an error.
-The correct way to distinguish an error from a symbol whose value is NULL
-is to call
-.BR dlerror (3)
-to clear any old error conditions, then call
-.BR dlsym (),
-and then call
-.BR dlerror (3)
-again, saving its return value into a variable, and check whether
-this saved value is not NULL.
-.P
-There are two special pseudo-handles that may be specified in
-.IR handle :
-.TP
-.B RTLD_DEFAULT
-Find the first occurrence of the desired symbol
-using the default shared object search order.
-The search will include global symbols in the executable
-and its dependencies,
-as well as symbols in shared objects that were dynamically loaded with the
-.B RTLD_GLOBAL
-flag.
-.TP
-.B RTLD_NEXT
-Find the next occurrence of the desired symbol in the search order
-after the current object.
-This allows one to provide a wrapper
-around a function in another shared object, so that, for example,
-the definition of a function in a preloaded shared object
-(see
-.B LD_PRELOAD
-in
-.BR ld.so (8))
-can find and invoke the "real" function provided in another shared object
-(or for that matter, the "next" definition of the function in cases
-where there are multiple layers of preloading).
-.P
-The
-.B _GNU_SOURCE
-feature test macro must be defined in order to obtain the
-definitions of
-.B RTLD_DEFAULT
-and
-.B RTLD_NEXT
-from
-.IR <dlfcn.h> .
-.P
-The function
-.BR dlvsym ()
-does the same as
-.BR dlsym ()
-but takes a version string as an additional argument.
-.SH RETURN VALUE
-On success,
-these functions return the address associated with
-.IR symbol .
-On failure, they return NULL;
-the cause of the error can be diagnosed using
-.BR dlerror (3).
-.SH ATTRIBUTES
-For an explanation of the terms used in this section, see
-.BR attributes (7).
-.TS
-allbox;
-lbx lb lb
-l l l.
-Interface Attribute Value
-T{
-.na
-.nh
-.BR dlsym (),
-.BR dlvsym ()
-T} Thread safety MT-Safe
-.TE
-.SH STANDARDS
-.TP
-.BR dlsym ()
-POSIX.1-2008.
-.TP
-.BR dlvsym ()
-GNU.
-.SH HISTORY
-.TP
-.BR dlsym ()
-glibc 2.0.
-POSIX.1-2001.
-.TP
-.BR dlvsym ()
-glibc 2.1.
-.SH NOTES
-There are several scenarios when the address of a global symbol is NULL.
-For example, a symbol can be placed at zero address by the linker, via
-a linker script or with
-.I \-\-defsym
-command-line option.
-Undefined weak symbols also have NULL value.
-Finally, the symbol value may be the result of
-a GNU indirect function (IFUNC) resolver function that returns
-NULL as the resolved value.
-In the latter case,
-.BR dlsym ()
-also returns NULL without error.
-However, in the former two cases, the
-behavior of GNU dynamic linker is inconsistent: relocation processing
-succeeds and the symbol can be observed to have NULL value, but
-.BR dlsym ()
-fails and
-.BR dlerror ()
-indicates a lookup error.
-.\"
-.SS History
-The
-.BR dlsym ()
-function is part of the dlopen API, derived from SunOS.
-That system does not have
-.BR dlvsym ().
-.SH EXAMPLES
-See
-.BR dlopen (3).
-.SH SEE ALSO
-.BR dl_iterate_phdr (3),
-.BR dladdr (3),
-.BR dlerror (3),
-.BR dlinfo (3),
-.BR dlopen (3),
-.BR ld.so (8)