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+'\" et
+.TH DLSYM "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
+.\"
+.SH PROLOG
+This manual page is part of the POSIX Programmer's Manual.
+The Linux implementation of this interface may differ (consult
+the corresponding Linux manual page for details of Linux behavior),
+or the interface may not be implemented on Linux.
+.\"
+.SH NAME
+dlsym
+\(em get the address of a symbol from a symbol table handle
+.SH SYNOPSIS
+.LP
+.nf
+#include <dlfcn.h>
+.P
+void *dlsym(void *restrict \fIhandle\fP, const char *restrict \fIname\fP);
+.fi
+.SH DESCRIPTION
+The
+\fIdlsym\fR()
+function shall obtain the address of a symbol (a function identifier or
+a data object identifier) defined in the symbol table identified by the
+.IR handle
+argument. The
+.IR handle
+argument is a symbol table handle returned from a call to
+\fIdlopen\fR()
+(and which has not since been released by a call to
+\fIdlclose\fR()),
+and
+.IR name
+is the symbol's name as a character string. The return value from
+\fIdlsym\fR(),
+cast to a pointer to the type of the named symbol, can be used to call
+(in the case of a function) or access the contents of (in the case of
+a data object) the named symbol.
+.P
+The
+\fIdlsym\fR()
+function shall search for the named symbol in the symbol table
+referenced by
+.IR handle .
+If the symbol table was created with lazy loading
+(see RTLD_LAZY in
+\fIdlopen\fR()),
+load ordering shall be used in
+\fIdlsym\fR()
+operations to relocate executable object files needed to resolve the
+symbol. The symbol resolution algorithm used shall be dependency order
+as described in
+\fIdlopen\fR().
+.P
+The RTLD_DEFAULT and RTLD_NEXT symbolic constants (which may be defined in
+.IR <dlfcn.h> )
+are reserved for future use as special values that applications may be
+allowed to use for
+.IR handle .
+.SH "RETURN VALUE"
+Upon successful completion, if
+.IR name
+names a function identifier,
+\fIdlsym\fR()
+shall return the address of the function converted from type pointer to
+function to type pointer to
+.BR void ;
+otherwise,
+\fIdlsym\fR()
+shall return the address of the data object associated with the data
+object identifier named by
+.IR name
+converted from a pointer to the type of the data object to a pointer to
+.BR void .
+If
+.IR handle
+does not refer to a valid symbol table handle or if the symbol named by
+.IR name
+cannot be found in the symbol table associated with
+.IR handle ,
+\fIdlsym\fR()
+shall return a null pointer.
+.P
+More detailed diagnostic information shall be available through
+\fIdlerror\fR().
+.SH ERRORS
+No errors are defined.
+.LP
+.IR "The following sections are informative."
+.SH "EXAMPLES"
+The following example shows how
+\fIdlopen\fR()
+and
+\fIdlsym\fR()
+can be used to access either a function or a data object. For simplicity,
+error checking has been omitted.
+.sp
+.RS 4
+.nf
+
+void *handle;
+int (*fptr)(int), *iptr, result;
+/* open the needed symbol table */
+handle = dlopen("/usr/home/me/libfoo.so", RTLD_LOCAL | RTLD_LAZY);
+/* find the address of the function my_function */
+fptr = (int (*)(int))dlsym(handle, "my_function");
+/* find the address of the data object my_object */
+iptr = (int *)dlsym(handle, "my_OBJ");
+/* invoke my_function, passing the value of my_OBJ as the parameter */
+result = (*fptr)(*iptr);
+.fi
+.P
+.RE
+.SH "APPLICATION USAGE"
+The following special purpose values for
+.IR handle
+are reserved for future use and have the indicated meanings:
+.IP RTLD_DEFAULT 12
+The identifier lookup happens in the normal global scope; that is,
+a search for an identifier using
+.IR handle
+would find the same definition as a direct use of this identifier in
+the program code.
+.IP RTLD_NEXT 12
+Specifies the next executable object file after this one that defines
+.IR name .
+This one refers to the executable object file containing the invocation of
+\fIdlsym\fR().
+The next executable object file is the one found upon the application
+of a load order symbol resolution algorithm (see
+\fIdlopen\fR()).
+The next symbol is either one of global scope (because it was introduced
+as part of the original process image or because it was added with a
+\fIdlopen\fR()
+operation including the RTLD_GLOBAL flag), or is in an executable object
+file that was included in the same
+\fIdlopen\fR()
+operation that loaded this one.
+.P
+The RTLD_NEXT flag is useful to navigate an intentionally created
+hierarchy of multiply-defined symbols created through interposition. For
+example, if a program wished to create an implementation of
+\fImalloc\fR()
+that embedded some statistics gathering about memory allocations, such
+an implementation could use the real
+\fImalloc\fR()
+definition to perform the memory allocation \(em and itself only embed
+the necessary logic to implement the statistics gathering function.
+.P
+Note that conversion from a
+.BR "void *"
+pointer to a function pointer as in:
+.sp
+.RS 4
+.nf
+
+fptr = (int (*)(int))dlsym(handle, "my_function");
+.fi
+.P
+.RE
+.P
+is not defined by the ISO\ C standard. This standard requires this conversion to
+work correctly on conforming implementations.
+.SH RATIONALE
+None.
+.SH "FUTURE DIRECTIONS"
+None.
+.SH "SEE ALSO"
+.IR "\fIdlclose\fR\^(\|)",
+.IR "\fIdlerror\fR\^(\|)",
+.IR "\fIdlopen\fR\^(\|)"
+.P
+The Base Definitions volume of POSIX.1\(hy2017,
+.IR "\fB<dlfcn.h>\fP"
+.\"
+.SH COPYRIGHT
+Portions of this text are reprinted and reproduced in electronic form
+from IEEE Std 1003.1-2017, Standard for Information Technology
+-- Portable Operating System Interface (POSIX), The Open Group Base
+Specifications Issue 7, 2018 Edition,
+Copyright (C) 2018 by the Institute of
+Electrical and Electronics Engineers, Inc and The Open Group.
+In the event of any discrepancy between this version and the original IEEE and
+The Open Group Standard, the original IEEE and The Open Group Standard
+is the referee document. The original Standard can be obtained online at
+http://www.opengroup.org/unix/online.html .
+.PP
+Any typographical or formatting errors that appear
+in this page are most likely
+to have been introduced during the conversion of the source files to
+man page format. To report such errors, see
+https://www.kernel.org/doc/man-pages/reporting_bugs.html .