mono/web/jit-debug-sample

* A debugging session using a dynamically generated symbol file.

	Let's assume we have the following C# application which we want to debug:

	<pre>
	using System;

	public class Foo
	{
		public struct MyStruct {
			int a;
			long b;
			double c;
		}

		public static void Main ()
		{
			Int32 value = 5;
			long test = 512;

			MyStruct my_struct;
			my_struct.a = 5;
			my_struct.b = test;
			my_struct.c = 23323.5235;
		}
	}
	</pre>

	First of all, we need to compile it and create the .il files:

	<pre>
	$ mcs ./Foo.cs
	$ monodis /home/export/martin/MONO-LINUX/lib/corlib.dll > corlib.il
	$ monodis Foo.exe > Foo.il
	</pre>

	Now we can start the JIT in the debugger:

	<pre>
	$ gdb ~/monocvs/mono/mono/jit/mono
	(gdb) r --dwarf --debug Foo:Main ./Foo.exe
	Starting program: /home/martin/monocvs/mono/mono/jit/mono --dwarf --debug Foo:Main ./Foo.exe
	0x081e8911 in ?? ()
	(gdb) call mono_debug_make_symbols ()
	(gdb) add-symbol-file /tmp/Foo.o
	Reading symbols from /tmp/Foo.o...done.
	Current language:  auto; currently c++
	(gdb) frame
	#0  Foo.Main () at Foo.il:26
	26          // method line 2
	(gdb) n
	Foo.Main () at Foo.il:38
	38              IL_0000: ldc.i4.5
	(gdb) list
	33              .maxstack 2
	34              .locals (
	35                      int32   V_0,
	36                      int64   V_1,
	37                      valuetype MyStruct      V_2)
	38              IL_0000: ldc.i4.5
	39              IL_0001: stloc.0
	40              IL_0002: ldc.i4 512
	41              IL_0007: conv.i8
	42              IL_0008: stloc.1
	43              IL_0009: ldloca.s 2
	44              IL_000b: ldc.i4.5
	45              IL_000c: stfld  int32 .MyStruct::a
	46              IL_0011: ldloca.s 2
	47              IL_0013: ldloc.1
	48              IL_0014: stfld  int64 .MyStruct::b
	49              IL_0019: ldloca.s 2
	50              IL_001b: ldc.r8 23323.5
	51              IL_0024: stfld  float64 .MyStruct::c
	52              IL_0029: ret
	(gdb) until 52
	Foo.Main () at Foo.il:53
	53          }
	(gdb) info locals
	V_0 = 5
	V_1 = 512
	V_2 = {a = 5, b = 512, c = 23323.523499999999}
	</pre>

	As you see in this example, you need to know IL code to use this debugging method - but
	it may be the only way to debug a library.