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dlopen.3: Remove content migrated to new dlsym() page
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk
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@ -34,7 +34,7 @@
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.\"
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.TH DLOPEN 3 2015-03-29 "Linux" "Linux Programmer's Manual"
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.SH NAME
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dlclose, dlerror, dlopen, dlmopen, dlsym, dlvsym \-
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dlclose, dlerror, dlopen, dlmopen \-
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programming interface to dynamic linking loader
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.SH SYNOPSIS
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.B #include <dlfcn.h>
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@ -43,8 +43,6 @@ programming interface to dynamic linking loader
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.sp
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.B "char *dlerror(void);"
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.sp
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.BI "void *dlsym(void *" handle ", const char *" symbol );
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.sp
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.BI "int dlclose(void *" handle );
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.sp
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.B #define _GNU_SOURCE
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@ -53,8 +51,6 @@ programming interface to dynamic linking loader
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.sp
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.BI "void *dlmopen (Lmid_t " lmid ", const char *" filename ", int " flags );
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.sp
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.BI "void *dlvsym(void *" handle ", char *" symbol ", char *" version );
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.sp
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Link with \fI\-ldl\fP.
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.SH DESCRIPTION
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The functions described in this page
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@ -314,67 +310,6 @@ is NULL, then the only permitted value for
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.I lmid
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is
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.BR LM_ID_BASE .
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.\"
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.SS dlsym()
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The function
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.BR dlsym ()
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takes a "handle" of a dynamic loaded shared object returned by
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.BR dlopen ()
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and the
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null-terminated symbol name, returning the address where that symbol is
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loaded into memory.
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If the symbol is not found, in the specified
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object or any of the shared objects that were automatically loaded by
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.BR dlopen ()
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when that object was loaded,
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.BR dlsym ()
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returns NULL.
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(The search performed by
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.BR dlsym ()
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is breadth first through the dependency tree of these shared objects.)
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Since the value of the symbol could actually be NULL (so that a
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NULL return from
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.BR dlsym ()
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need not indicate an error), the correct way to test for an error
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is to call
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.BR dlerror ()
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to clear any old error conditions, then call
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.BR dlsym (),
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and then call
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.BR dlerror ()
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again, saving its return value into a variable, and check whether
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this saved value is not NULL.
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.PP
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There are two special pseudo-handles:
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.TP
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.B RTLD_DEFAULT
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Find the first occurrence of the desired symbol
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using the default shared object search order.
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The search will include global symbols in the executable
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and its dependencies,
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as well as symbols in shared objects that were dynamically loaded with the
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.BR RTLD_GLOBAL
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flag.
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.TP
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.BR RTLD_NEXT
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Find the next occurrence of the desired symbol in the search order
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after the current object.
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This allows one to provide a wrapper
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around a function in another shared object, so that, for example,
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the definition of a function in a preloaded shared object
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(see
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.B LD_PRELOAD
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in
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.BR ld.so (8))
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can find and invoke the "real" function provided in another shared object
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(or for that matter, the "next" definition of the function in cases
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where there are multiple layers of preloading).
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.SS dlvsym()
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The function
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.BR dlvsym ()
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does the same as
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.BR dlsym ()
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but takes a version string as an additional argument.
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.SS dlclose()
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The function
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.BR dlclose ()
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returns 0 on success, and nonzero on error.
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.SH VERSIONS
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.BR dlopen (),
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.BR dlsym (),
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.BR dlclose (),
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and
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.BR dlerror ()
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are present in glibc 2.0 and later.
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.BR dlmopen ()
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first appeared in glibc 2.3.4.
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.BR dlvsym ()
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first appeared in glibc 2.1.
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.SH CONFORMING TO
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POSIX.1-2001 describes
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.BR dlclose (),
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.BR dlerror (),
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.BR dlopen (),
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and
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.BR dlsym ().
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.BR dlopen ().
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The
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.BR dlmopen ()
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and
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.BR dlvsym ()
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functions are GNU extensions.
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function is a GNU extension.
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.SH NOTES
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The symbols
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.B RTLD_DEFAULT
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and
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.B RTLD_NEXT
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are defined by
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.I <dlfcn.h>
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only when
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.B _GNU_SOURCE
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was defined before including it.
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.\" .LP
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.\" The string returned by
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.\" .BR dlerror ()
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@ -544,11 +464,7 @@ permit multiple initialization and finalization functions to be defined.
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.\" .\" void _fini(void) __attribute__((destructor));
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.\"
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.SS History
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The dlopen interface standard comes from SunOS.
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That system does not have
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.BR dlvsym (),
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but does have
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.BR dlmopen ().
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These functions are part of the dlopen API, derived from SunOS.
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.SH EXAMPLE
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Load the math library, and print the cosine of 2.0:
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.nf
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@ -631,6 +547,7 @@ as the example name:
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.BR dl_iterate_phdr (3),
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.BR dladdr (3),
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.BR dlinfo (3),
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.BR dlsym (3),
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.BR rtld-audit (7),
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.BR ld.so (8),
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.BR ldconfig (8)
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