mono-shlib-cop (1)
Leading comments
mono-shlib-cop manual page. (C) 2005-2006 Jonathan Pryor Author: Jonathan Pryor (jonpryor@vt.edu)
NAME
mono-shlib-cop - Shared Library Usage CheckerSYNOPSIS
mono-shlib-cop [OPTIONS]* [ASSEMBLY-FILE-NAME]*OPTIONS
- -p, --prefixes=PREFIX
- Mono installation prefixes. This is to find $prefix/etc/mono/config. The default is based upon the location of mscorlib.dll, and is normally correct.
DESCRIPTION
mono-shlib-cop is a tool that inspects a managed assembly looking for erroneous or suspecious usage of shared libraries.The tool takes one or more assembly filenames, and inspects each assembly specified.
The errors checked for include:
- *
- Does the shared library exist?
- *
- Does the requested symbol exist within the shared library?
The warnings checked for include:
- *
- Is the target shared library a versioned library? (Relevant only on Unix systems, not Mac OS X or Windows.)
In general, only versioned libraries such as libc.so.6 are present on the user's machine, and efforts to load libc.so will result in a System.DllNotFoundException. There are three solutions to this:
- 1.
- Require that the user install any -devel packages which provide the unversioned library. This usually requires that the user install a large number of additional packages, complicating the installation process.
- 2.
- Use a fully versioned name in your DllImport statements. This requires editing your source code and recompiling whenever you need to target a different version of the shared library.
- 3.
- Provide an assembly.config file which contains <dllmap/> elements to remap the shared library name used by your assembly to the actual versioned shared library present on the users system. Mono provides a number of pre-existing <dllmap/> entries, including ones for libc.so and libX11.so.
EXAMPLE
The following code contains examples of the above errors and warnings:
using System.Runtime.InteropServices; // for DllImport
class Demo {
[DllImport ("bad-library-name")]
private static extern void BadLibraryName ();
[DllImport ("libc.so")]
private static extern void BadSymbolName ();
[DllImport ("libcap.so")]
private static extern int cap_clear (IntPtr cap_p);
}
- Bad library name
- Assuming that the library bad-library-name doesn't exist on your machine, Demo.BadLibraryName will generate an error, as it requires a shared library which cannot be loaded. This may be ignorable; see BUGS
- Bad symbol name
- Demo.BadSymbolName will generate an error, as libc.so (remapped to libc.so.6 by mono's $prefix/etc/mono/config file) doesn't contain the function BadSymbolName
- Unversioned library dependency
- Assuming you have the file libcap.so , Demo.cap_clear will generate a warning because, while libcap.so could be loaded, libcap.so might not exist on the users machine (on FC2, /lib/libcap.so is provided by libcap-devel , and you can't assume that end users will have any -devel packages installed).
FIXING CODE
The fix depends on the warning or error:- Bad library names
- Use a valid library name in the DllImport attribute, or provide a <dllmap/> entry to map your existing library name to a valid library name.
- Bad symbol names
- Reference a symbol that actually exists in the target library.
- Unversioned library dependency
- Provide a <dllmap/> entry to reference a properly versioned library, or ignore the warning (see BUGS ).
DLLMAP ENTRIES
Mono looks for an ASSEMBLY-NAME .config file for each assembly loaded, and reads this file to find Dll mapping information. For example, with mcs.exe , Mono would read mcs.exe.config , and for Mono.Posix.dll , Mono would read Mono.Posix.dll.config .The .config file is an XML document containing a top-level <configuration/> section with nested <dllmap/> entries, which contains dll and target attributes. The dll attribute should contain the same string used in your DllImport attribute value, and the target attribute specifies which shared library mono should actually load at runtime.
A sample .config file is:
<configuration>
<dllmap dll="gtkembedmoz" target="libgtkembedmoz.so" />
</configuration>
BUGS
- *
-
Only
DllImport
entries are checked; the surrounding IL is ignored. Consequently, if a runtime
check is performed to choose which shared library to invoke, an error will be
reported even though the specified library is never used. Consider this code:
using System.Runtime.InteropServices; // for DllImport class Beep { [DllImport ("kernel32.dll")] private static extern int Beep (int dwFreq, int dwDuration); [DllImport ("libcurses.so")] private static extern int beep (); public static void Beep () { if (System.IO.Path.DirectorySeparatorChar == '\\') { Beep (750, 300); } else { beep (); } } }If mono-shlib-cop is run on this assembly, an error will be reported for using kernel32.dll , even though kernel32.dll will never be used on Unix platforms. - *
-
mono-shlib-cop
currently only examines the shared library file extension to determine if a
warning should be generated. A
.so
extension will always generate a warning, even if the
.so
is not a symlink,
isn't provided in a
-devel
package, and there is no versioned shared library
(possible examples including
/usr/lib/libtcl8.4.so,
/usr/lib/libubsec.so,
etc.).
Consequently, warnings for any such libraries are useless, and incorrect.
Windows and Mac OS X will never generate warnings, as these platforms use different shared library extensions.