SIGSEGV when P / Invoking dlopen
I am trying to write an abstraction for loading dynamic libraries on Windows and Linux. Although everything goes well on the Windows platform, I get SIGSEGV when I call dlopen
:
// File: Main.cs
using System;
using System.Runtime.InteropServices;
namespace DlopenTest
{
class MainClass
{
const int RTLD_NOW = 2;
[DllImport("dl")]
static extern IntPtr dlopen([MarshalAs(UnmanagedType.LPTStr)] string filename, int flags);
[DllImport("dl")]
static extern IntPtr dlsym(IntPtr handle, [MarshalAs(UnmanagedType.LPTStr)] string symbol);
public static void Main (string[] args)
{
IntPtr libraryHandle = dlopen("libc.so.6", RTLD_NOW);
Console.WriteLine ("Success!");
}
}
}
The conclusion is as follows:
Stacktrace:
at (wrapper managed-to-native) DlopenTest.MainClass.dlopen (string,int) <0x00004>
at (wrapper managed-to-native) DlopenTest.MainClass.dlopen (string,int) <0x00004>
at DlopenTest.MainClass.Main (string[]) [0x00000] in /home/luca/Projects/DlopenTest/DlopenTest/Main.cs:18
at (wrapper runtime-invoke) <Module>.runtime_invoke_void_object (object,intptr,intptr,intptr) <IL 0x0001d, 0x00043>
Native stacktrace:
/usr/bin/mono() [0x80d5b19]
/usr/bin/mono() [0x810f7ab]
[0xb771940c]
/lib/ld-linux.so.2(+0x119a8) [0xb772b9a8]
/usr/lib/libdl.so(+0xc0b) [0xb536dc0b]
/lib/ld-linux.so.2(+0xdb36) [0xb7727b36]
/usr/lib/libdl.so(+0x109c) [0xb536e09c]
/usr/lib/libdl.so(dlopen+0x41) [0xb536db41]
[0xb58672f1]
[0xb58671bd]
[0xb5867234]
/usr/bin/mono() [0x8064428]
/usr/bin/mono(mono_runtime_invoke+0x40) [0x812d4e0]
/usr/bin/mono(mono_runtime_exec_main+0xde) [0x8130f8e]
/usr/bin/mono(mono_runtime_run_main+0x112) [0x8131292]
/usr/bin/mono(mono_main+0x15ec) [0x80b3bdc]
/usr/bin/mono() [0x805b675]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe6) [0xb74b8ca6]
/usr/bin/mono() [0x805b5b1]
Debug info from gdb:
=================================================================
Got a SIGSEGV while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================
What's happening?
My glibc version is 2.11.3 and battery life is 2.6.3.
To compile the program: mono-csc Main.cs
To run the program:./Main.exe
I just paused a test application. Here are the system calls before SIGSGV:
...
open("/usr/lib/libdl.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0@\n\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=9736, ...}) = 0
mmap2(NULL, 12408, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb598b000
mmap2(0xb598d000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1) = 0xb598d000
close(3) = 0
mprotect(0xb598d000, 4096, PROT_READ) = 0
munmap(0xb598f000, 76774) = 0
gettimeofday({1333269422, 515602}, NULL) = 0
gettimeofday({1333269422, 515653}, NULL) = 0
gettimeofday({1333269422, 515828}, NULL) = 0
gettimeofday({1333269422, 515884}, NULL) = 0
gettimeofday({1333269422, 515986}, NULL) = 0
gettimeofday({1333269422, 516059}, NULL) = 0
gettimeofday({1333269422, 516613}, NULL) = 0
gettimeofday({1333269422, 516670}, NULL) = 0
brk(0x98e3000) = 0x98e3000
brk(0x98e1000) = 0x98e1000
gettimeofday({1333269422, 516916}, NULL) = 0
brk(0x98de000) = 0x98de000
brk(0x98dc000) = 0x98dc000
brk(0x98db000) = 0x98db000
gettimeofday({1333269422, 517092}, NULL) = 0
gettimeofday({1333269422, 517200}, NULL) = 0
gettimeofday({1333269422, 517261}, NULL) = 0
gettimeofday({1333269422, 517368}, NULL) = 0
gettimeofday({1333269422, 517525}, NULL) = 0
gettimeofday({1333269422, 517762}, NULL) = 0
gettimeofday({1333269422, 517823}, NULL) = 0
gettimeofday({1333269422, 518007}, NULL) = 0
gettimeofday({1333269422, 518074}, NULL) = 0
gettimeofday({1333269422, 518435}, NULL) = 0
gettimeofday({1333269422, 518486}, NULL) = 0
gettimeofday({1333269422, 518648}, NULL) = 0
gettimeofday({1333269422, 518699}, NULL) = 0
gettimeofday({1333269422, 518803}, NULL) = 0
futex(0xb598e06c, FUTEX_WAKE_PRIVATE, 2147483647) = 0
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
This trace is generated by calling " strace /opt/mono-2.10/bin/mono ./DlopenTest.exe 2> strace
"
The complexity of the default mono setup (2.6) is almost the same and always fails at one point.
How do I debug this condition? I have no idea ... Maybe dlopen is just a wrapper so I can name an alternative function? Perhaps I am doing mono 2.10 in the wrong environement (maybe I need to specify some environment variable to get this working)?
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Your code is working on Mono 2.10.
$ mono --version
Mono JIT compiler version 2.10.5 (Debian 2.10.5-1)
Copyright (C) 2002-2011 Novell, Inc, Xamarin, Inc and Contributors. www.mono-project.com
TLS: __thread
SIGSEGV: altstack
Notifications: epoll
Architecture: x86
Disabled: none
Misc: softdebug
LLVM: supported, not enabled.
GC: Included Boehm (with typed GC and Parallel Mark)
$ cat so.cs
using System;
using System.Runtime.InteropServices;
namespace DlopenTest
{
class MainClass
{
const int RTLD_NOW = 2;
[DllImport("dl")]
static extern IntPtr dlopen([MarshalAs(UnmanagedType.LPTStr)] string filename, int flags);
[DllImport("dl")]
static extern IntPtr dlsym(IntPtr handle, [MarshalAs(UnmanagedType.LPTStr)] string symbol);
public static void Main (string[] args)
{
IntPtr libraryHandle = dlopen("libc.so.6", RTLD_NOW);
Console.WriteLine ("Success!");
}
}
}
$ mcs so.cs
so.cs(18,20): warning CS0219: The variable `libraryHandle' is assigned but its value is never used
Compilation succeeded - 1 warning(s)
$ mono so.exe
Success!
It seems to have failed under 2.6 (which is something pretty common), but this version, if I'm many years old ... I highly recommend you upgrade.
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This is a well known bug in many different versions of Mono. Here is a working solution: https://bugzilla.xamarin.com/show_bug.cgi?id=4190
In short: create a simple C / C ++ wrapper for libdl.so (libfakedl.so) and tap its functions through the wrapper.
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