mirror of https://github.com/mkerrisk/man-pages
Formatting changes, and minor rewordings.
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Michael Kerrisk
parent
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@ -52,7 +52,7 @@ The four functions
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.BR dlclose (),
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.BR dlerror ()
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implement the interface to the dynamic linking loader.
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.SS "dlerror"
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.SS "dlerror()"
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The function
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.BR dlerror ()
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returns a human readable string describing the most recent error
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@ -65,7 +65,7 @@ since the last call to
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.BR dlerror () .
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It returns NULL if no errors have occurred since initialization or since
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it was last called.
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.SS "dlopen"
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.SS "dlopen()"
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The function
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.BR dlopen ()
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loads the dynamic library file named by the null-terminated
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@ -83,7 +83,7 @@ Otherwise, the dynamic linker searches for the library as follows
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(see
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.BR ld.so (8)
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for further details):
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.IP o
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.IP o 4
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(ELF only) If the executable file for the calling program
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contains a DT_RPATH tag, and does not contain a DT_RUNPATH tag,
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then the directories listed in the DT_RPATH tag are searched.
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@ -220,7 +220,7 @@ has been called on it as many times as
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.BR dlopen ()
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has succeeded on it.
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The
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.B _init
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.BR _init ()
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routine, if present, is only called once.
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But a subsequent call with
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.B RTLD_NOW
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@ -230,7 +230,7 @@ may force symbol resolution for a library earlier loaded with
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If
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.BR dlopen ()
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fails for any reason, it returns NULL.
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.SS "dlsym"
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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 library returned by
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@ -271,7 +271,7 @@ will find the next occurrence of a function in the search order
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after the current library.
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This allows one to provide a wrapper
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around a function in another shared library.
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.SS "dlclose"
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.SS "dlclose()"
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The function
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.BR dlclose ()
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decrements the reference count on the dynamic library handle
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@ -282,22 +282,24 @@ symbols in it, then the dynamic library is unloaded.
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The function
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.BR dlclose ()
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returns 0 on success, and non-zero on error.
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.SS "The obsolete symbols _init and _fini"
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.SS "The obsolete symbols _init() and _fini()"
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The linker recognizes special symbols
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.B _init
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and
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.BR _fini .
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If a dynamic library exports a routine named
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.BR _init ,
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.BR _init (),
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then that code is executed after the loading, before
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.BR dlopen ()
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returns.
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If the dynamic library exports a routine named
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.BR _fini ,
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.BR _fini (),
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then that routine is called just before the library is unloaded.
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In case you need to avoid linking against the system startup files,
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this can be done by giving gcc the "\-nostartfiles" parameter on
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the command line.
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this can be done by using the
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.BR gcc (1)
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.I \-nostartfiles"
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command-line option.
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.LP
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Using these routines, or the gcc
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.B \-nostartfiles
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@ -338,16 +340,19 @@ The function
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takes a function pointer and tries to resolve name
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and file where it is located.
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Information is stored in the
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Dl_info structure:
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.I Dl_info
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structure:
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.sp
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.in +0.25i
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.nf
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typedef struct {
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const char *dli_fname;/* Filename of defining object */
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void *dli_fbase; /* Load address of that object */
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const char *dli_sname;/* Name of nearest lower symbol */
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void *dli_saddr; /* Exact value of nearest symbol */
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const char *dli_fname; /* Filename of defining object */
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void *dli_fbase; /* Load address of that object */
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const char *dli_sname; /* Name of nearest lower symbol */
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void *dli_saddr; /* Exact value of nearest symbol */
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} Dl_info;
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.fi
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.in
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.sp
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.BR dladdr ()
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returns 0 on error, and non-zero on success.
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@ -390,9 +395,7 @@ but not
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.BR dlvsym ().
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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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.RS
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.nf
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.if t .ft CW
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#include <stdio.h>
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#include <stdlib.h>
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@ -424,9 +427,7 @@ main(int argc, char **argv)
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dlclose(handle);
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exit(EXIT_SUCCESS);
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}
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.if t .ft P
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.fi
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.RE
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.PP
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If this program were in a file named "foo.c", you would build the program
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with the following command:
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@ -435,8 +436,12 @@ with the following command:
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gcc \-rdynamic \-o foo foo.c \-ldl
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.RE
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.PP
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Libraries exporting _init() and _fini() will want to be compiled as
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follows, using bar.c as the example name:
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Libraries exporting
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.BR _init ()
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and
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.BR _fini ()
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will want to be compiled as
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follows, using \fIbar.c\fP as the example name:
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.RS
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.LP
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gcc \-shared \-nostartfiles \-o bar bar.c
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