.\" Copyright (c) 2007-2020 Daniel Adler <dadler AT uni-goettingen DOT de>,
.\"                         Tassilo Philipp <tphilipp AT potion-studios DOT com>
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.Dd $Mdocdate$
.Dt dynload 3
.Sh NAME
.Nm dynload
.Nd encapsulates dynamic loading mechanisms and
gives access to functions in foreign dynamic libraries and code modules.
.Sh SYNOPSIS
.In dynload.h
.Ft DLLib *
.Fn dlLoadLibrary "const char * libpath"
.Ft void
.Fn dlFreeLibrary "DLLib * pLib"
.Ft void *
.Fn dlFindSymbol "DLLib * pLib" "const char * pSymbolName"
.Ft int
.Fn dlGetLibraryPath "DLLib * pLib" "char * sOut" "int bufSize"
.Ft DLSyms*
.Fn dlSymsInit "const char * libPath"
.Ft void
.Fn dlSymsCleanup "DLSyms * pSyms"
.Ft int
.Fn dlSymsCount "DLSyms * pSyms"
.Ft const char*
.Fn dlSymsName "DLSyms * pSyms" "int index"
.Ft const char*
.Fn dlSymsNameFromValue "DLSyms * pSyms" "void * value"
.Sh DESCRIPTION
The
.Nm
library provides an interface to load foreign dynamic libraries and access
to their symbols.
.Pp
.Fn dlLoadLibrary
loads a dynamic library at
.Ar libpath
and returns a handle to it for use in
.Fn dlFreeLibrary 
and
.Fn dlFindSymbol
calls. Passing a null pointer for the
.Ar libpath
argument is valid, and returns a handle to the main executable of the calling code. Also, searching libraries in library paths (e.g. by just passing the library's leaf name) should work, however, they are OS specific. The
.Ar libPath
argument is expected to be UTF-8 encoded. Returns a null pointer on error.
.Pp
.Fn dlFreeLibrary 
frees the loaded library with handle
.Ar pLib .
.Pp
.Fn dlFindSymbol
returns a pointer to a symbol with name
.Ar pSymbolName
in the library with handle
.Ar pLib ,
or returns a null pointer if the symbol cannot be found. The name is specified as it would appear in C source code (mangled if C++, etc.).
.Pp
.Fn dlGetLibraryPath
can be used to get a copy of the path to the library loaded with handle
.Ar pLib .
The parameter
.Ar sOut
is a pointer to a buffer of size
.Ar bufSize
(in bytes), to hold the output string (UTF-8 encoded). The return value is the size of the buffer (in bytes) needed to hold the null-terminated string, or 0 if it can't be looked up. If
.Ar bufSize
>= return value >= 1, a null-terminted string with the path to the library should be in
.Ar sOut .
If it returns 0, the library name wasn't able to be found. Please note that this might happen in some rare cases, so make sure to always check. Passing a null pointer as
.Ar pLib
returns the path to the executable (not guaranteed to be absolute - if it isn't it's relative to the working directory the process was started in, not the current one).
.Pp
The dlSyms* functions can be used to iterate over symbols. Since they can be used on libraries that are not linked, they are made
for symbol name lookups, not to get symbols' addresses. For that refer to
.Fn dlFindSymbol .
.Fn dlSymsInit
will return a handle (or null pointer on error) to the shared object specified by
.Ar libPath ,
to be used with the other dlSyms* functions. Note that contrary to loading and linking libraries, no (OS-specific) rules for searching libraries in library paths, etc. apply. The handle must be freed with
.Fn dlSymsCleanup .
.Fn dlSymsCount
returns the number of symbols in the shared object,
.Fn dlSymsName
and
.Fn dlSymsNameFromValue
are used to lookup symbol names using an index or symbol's address, respectively, returning a null pointer on error. The names are returned as they would appear in C source code (mangled if C++, etc.). The address passed to
.Fn dlSymsNameFromValue
must point to a loaded symbol.
.Sh NOTES
.Fn dlLoadLibrary
does handle loading dylibs on macos >= 11.0.1 that aren't on the file system but are provided through the OS' "built-in dynamic linker cache of all system-provided libraries" (to load, use same "path" as one would with dlopen(3)).
.Sh BUGS
.Fn dlGetLibraryPath
is not thread-safe on Darwin (macOS, iOS, ...) and OpenBSD.
.Pp
.Fn dlSymsInit
is not thread-safe on Darwin.
.Pp
.Fn dlGetLibraryPath
will not work on the following platforms when the library in question doesn't have the (default)
.Fn _init
and
.Fn _fini
symbols exported (rare, but possible): Haiku (all versions), OpenBSD < 3.7, NetBSD < 5.1, FreeBSD < 4.8
.Pp
Getting the executable's path by passing NULL in
.Ar pLib
to
.Fn dlGetLibraryPath
fails on the following platforms: Haiku (all versions), OpenBSD < 3.7, NetBSD < 5.1, FreeBSD < 4.8
.Sh CONFORMING TO
The dynload library conforms to c99.
.Ed
.Sh SEE ALSO
.Xr dyncall 3 ,
.Xr dyncallback 3
and the dyncall manual (available in HTML and PDF format) for more information.
.Sh AUTHORS
.An "Daniel Adler" Aq dadler@uni-goettingen.de
.An "Tassilo Philipp" Aq tphilipp@potion-studios.com