freebsd-dev/lib/libc/gen/dladdr.3

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.Dd February 5, 1998
.Dt DLADDR 3
.Os
.Sh NAME
.Nm dladdr
.Nd find the shared object containing a given address
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In dlfcn.h
.Ft int
.Fn dladdr "const void *addr" "Dl_info *info"
.Sh DESCRIPTION
The
.Fn dladdr
function
queries the dynamic linker for information about the shared object
containing the address
.Fa addr .
The information is returned in the structure specified by
.Fa info .
The structure contains at least the following members:
.Bl -tag -width "XXXconst char *dli_fname"
.It Li "const char *dli_fname"
The pathname of the shared object containing the address.
.It Li "void *dli_fbase"
The base address at which the shared object is mapped into the
address space of the calling process.
.It Li "const char *dli_sname"
The name of the nearest run-time symbol with a value less than or
equal to
.Fa addr .
When possible, the symbol name is returned as it would appear in C
source code.
.Pp
If no symbol with a suitable value is found, both this field and
.Va dli_saddr
are set to
.Dv NULL .
.It Li "void *dli_saddr"
The value of the symbol returned in
.Li dli_sname .
.El
.Pp
The
.Fn dladdr
function
is available only in dynamically linked programs.
.Sh ERRORS
If a mapped shared object containing
.Fa addr
cannot be found,
.Fn dladdr
returns 0.
In that case, a message detailing the failure can be retrieved by
calling
.Fn dlerror .
.Pp
On success, a non-zero value is returned.
.Sh SEE ALSO
.Xr rtld 1 ,
.Xr dlopen 3
.Sh HISTORY
The
.Fn dladdr
function first appeared in the Solaris operating system.
.Sh BUGS
This implementation is bug-compatible with the Solaris
implementation.
In particular, the following bugs are present:
.Bl -bullet
.It
If
.Fa addr
lies in the main executable rather than in a shared library, the
pathname returned in
.Va dli_fname
may not be correct.
The pathname is taken directly from
.Va argv[0]
of the calling process.
When executing a program specified by its
full pathname, most shells set
.Va argv[0]
to the pathname.
But this is not required of shells or guaranteed
by the operating system.
.It
If
.Fa addr
is of the form
.Va &func ,
where
.Va func
is a global function, its value may be an unpleasant surprise.
In
dynamically linked programs, the address of a global function is
considered to point to its program linkage table entry, rather than to
the entry point of the function itself.
This causes most global
functions to appear to be defined within the main executable, rather
than in the shared libraries where the actual code resides.
.It
Returning 0 as an indication of failure goes against long-standing
Unix tradition.
.El