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Rewrote discussion of dlopen() 'flag' argument; 

added description of RTLD_NOLOAD and RTLD_DELETE.
This commit is contained in:
Michael Kerrisk 2006-01-14 04:29:47 +00:00
parent e75529df3b
commit 336e88f0f8
1 changed files with 49 additions and 20 deletions
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69
man3/dlopen.3
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@ -117,36 +117,65 @@ then these are also automatically loaded by the dynamic linker
using the same rules. (This process may occur recursively,
if those libraries in turn have dependencies, and so on.)
.PP
The value of
.I flag
can be either
One of the following two values must be included in
.IR flag :
.TP
.B RTLD_LAZY
or
.BR RTLD_NOW .
When
Perform lazy binding.
Only resolve undefined symbols as the code that referenced
them is executed.
If the symbol is never referenced, then it is never resolved.
(Lazy binding is only performed for function references;
references to variables are always immediately bound when
the library is loaded.)
.TP
.B RTLD_NOW
is specified, or the environment variable
If this value is specified, or the environment variable
.B LD_BIND_NOW
is set to a non-empty string,
all undefined symbols in the library are resolved before
.BR dlopen ()
returns. If this cannot be done, an error is returned.
Otherwise binding is lazy: symbol values are first resolved
when needed.
.PP
Optionally,
Zero of more of the following values may also be ORed in
.IR flag :
.TP
.B RTLD_GLOBAL
may be or'ed into
.IR flag ,
in which case the external symbols defined in the library will be
The external symbols defined in the library will be
made available for symbol resolution of subsequently loaded libraries.
(The converse of
.B RTLD_GLOBAL
is
.BR RTLD_LOCAL .
.\" that indicates that the symbols in this library should not be made
.\" available for resolution of symbols of subsequently loaded libraries.
This is the default.)
.TP
.B RTLD_LOCAL
This is the converse of
.BR RTLD_GLOBAL ,
and the default if neither flag is specified.
Symbols defined in this library are not made available to resolve
references in subsequently loaded libraries.
.TP
.BR RTLD_NODELETE " (since glibc 2.2)
Do not unload the library during
.BR dlclose ().
Consequently, the library's static variables are not reinitialised
if the library is reloaded with
.BR dlopen ()
at a later time.
This flag is not specified in POSIX.1-2001.
.\" (But it is present on Solaris.)
.TP
.BR RTLD_NOLOAD " (since glibc 2.2)
Don't load the library.
This can be used to test if the library is already resident
.RB ( dlopen ()
returns NULL if it is not, or the library's handle if it is resident).
This flag can also be used to promote the flags on a library
that is already loaded.
For example, a library that was previously loaded with
.B RTLD_LOCAL
can be re-opened with
.BR RTLD_NOLOAD\ |\ RTLD_GLOBAL .
This flag is not specified in POSIX.1-2001.
.\" (But it is present on Solaris.)
.\"
.\" FIXME: document RTLD_DEEPBIND (new in glibc 2.3.4).
.PP
If
.I filename