Hello,
maybe there might be a problem with a optimization in the jump
trampoline code. In the IL code example appended, the main method
creates two threads that start with a method that jumps to a
synchronized method. The final value of the variable "count"
should be 20, but it isn't always so. If you change the jump
instruction to call instruction, the code works as expected. I
tested with Mono 2.6.1, 2.6.7 and 2.10.2 on an x86 machine
running Linux.
In "mono_postprocess_patches()", the handle to the method is stored
in the hash table "jump_target_hash". When the synchronized method
("tolleMethode()") is jumped to the first time, the magic trampoline
creates a wrapper and returns the address of the wrapper. The first
jump instruction is patched with that address. A later lookup in the
"jump_target_hash" ("mono_jit_compile_method_inner()", in the scope
of the JIT-compilation of the wrapper) doesn't return pending jump
patches because the method handle of "tolleMethod()" is stored,
instead of the wrapper's handle. So, the second jump instruction
is not patched (if it is JIT-compiled so far).
Even worse: When the wrapper is executed, the method "tolleMethode()"
is JIT-compiled. Then, in "mono_jit_compile_method_inner()", there
is a hash hit and the second jump instruction is patched with
the method's address instead of her wrapper's one. So, I suggest to
check for a synchronized method in "mono_postprocess_patches()",
to create a wrapper if needed and to change the patch's target
method to the wrapper. There might be other problems I don't see?
With kind regards,
Martin Däumler
.assembly extern mscorlib
{
.ver 1:0:5000:0
.publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) // .z\V.4..
}
.assembly 'thread-jump'
{
.hash algorithm 0x00008004
.ver 0:0:0:0
}
.module 'thread-jump.exe' // GUID = {DE2D75CD-6E25-4FD7-AB97-77B5E7FF5D5D}
.class private auto ansi beforefieldinit TestClass
extends [mscorlib]System.Object
{
.field private static int32 count
// method line 1
.method public hidebysig specialname rtspecialname
instance default void '.ctor' () cil managed
{
// Method begins at RVA 0x20ec
// Code size 7 (0x7)
.maxstack 8
IL_0000: ldarg.0
IL_0001: call instance void object::'.ctor'()
IL_0006: ret
} // end of method TestClass::.ctor
// method line 2
.method private static specialname rtspecialname
default void '.cctor' () cil managed
{
// Method begins at RVA 0x20f4
// Code size 1 (0x1)
.maxstack 8
IL_0000: ret
} // end of method TestClass::.cctor
// method line 3
.method public static hidebysig
default void tolleMethode () cil managed synchronized
{
// Method begins at RVA 0x20f8
// Code size 71 (0x47)
.maxstack 6
.locals init (
int32 V_0,
int32 V_1)
IL_0000: ldc.i4.0
IL_0001: stloc.0
IL_0002: br IL_0025
IL_0007: ldloc.0
IL_0008: ldc.i4.1
IL_0009: add
IL_000a: stloc.0
IL_000b: ldsfld int32 TestClass::count
IL_0010: stloc.1
IL_0011: ldloc.1
IL_0012: ldc.i4.1
IL_0013: add
IL_0014: stloc.1
IL_0015: ldc.i4 200
IL_001a: call void class
[mscorlib]System.Threading.Thread::Sleep(int32)
IL_001f: ldloc.1
IL_0020: stsfld int32 TestClass::count
IL_0025: ldloc.0
IL_0026: ldc.i4.s 0x0a
IL_0028: blt IL_0007
IL_002d: ldstr "count: "
IL_0032: ldsflda int32 TestClass::count
IL_0037: call instance string int32::ToString()
IL_003c: call string string::Concat(string, string)
IL_0041: call void class [mscorlib]System.Console::WriteLine(string)
IL_0046: ret
} // end of method TestClass::tolleMethode
// method line 4
.method public static hidebysig
default void jumpStart1 () cil managed
{
// Method begins at RVA 0x214c
// Code size 6 (0x6)
.maxstack 8
// IL_0000: call void class TestClass::tolleMethode()
IL_0000: jmp void class TestClass::tolleMethode()
IL_0005: ret
} // end of method TestClass::jumpStart1
// method line 5
.method public static hidebysig
default void jumpStart2 () cil managed
{
// Method begins at RVA 0x2154
// Code size 6 (0x6)
.maxstack 8
// IL_0000: call void class TestClass::tolleMethode()
IL_0000: jmp void class TestClass::tolleMethode()
IL_0005: ret
} // end of method TestClass::jumpStart2
// method line 6
.method private static hidebysig
default void Main () cil managed
{
// Method begins at RVA 0x215c
.entrypoint
// Code size 65 (0x41)
.maxstack 8
.locals init (
class [mscorlib]System.Threading.ThreadStart V_0,
class [mscorlib]System.Threading.ThreadStart V_1,
class [mscorlib]System.Threading.Thread V_2,
class [mscorlib]System.Threading.Thread V_3)
IL_0000: ldnull
IL_0001: ldftn void class TestClass::jumpStart1()
IL_0007: newobj instance void class
[mscorlib]System.Threading.ThreadStart::'.ctor'(object, native int)
IL_000c: stloc.0
IL_000d: ldnull
IL_000e: ldftn void class TestClass::jumpStart2()
IL_0014: newobj instance void class
[mscorlib]System.Threading.ThreadStart::'.ctor'(object, native int)
IL_0019: stloc.1
IL_001a: ldloc.0
IL_001b: newobj instance void class
[mscorlib]System.Threading.Thread::'.ctor'(class
[mscorlib]System.Threading.ThreadStart)
IL_0020: stloc.2
IL_0021: ldloc.1
IL_0022: newobj instance void class
[mscorlib]System.Threading.Thread::'.ctor'(class
[mscorlib]System.Threading.ThreadStart)
IL_0027: stloc.3
IL_0028: ldloc.2
IL_0029: callvirt instance void class
[mscorlib]System.Threading.Thread::Start()
IL_002e: ldloc.3
IL_002f: callvirt instance void class
[mscorlib]System.Threading.Thread::Start()
IL_0034: ldloc.2
IL_0035: callvirt instance void class
[mscorlib]System.Threading.Thread::Join()
IL_003a: ldloc.3
IL_003b: callvirt instance void class
[mscorlib]System.Threading.Thread::Join()
IL_0040: ret
} // end of method TestClass::Main
} // end of class TestClass
.class private auto ansi sealed SampleDelegate
extends [mscorlib]System.MulticastDelegate
{
// method line 7
.method public hidebysig specialname rtspecialname
instance default void '.ctor' (object 'object', native int 'method')
runtime managed
{
// Method begins at RVA 0x0
// Disassembly of native methods is not supported
} // end of method SampleDelegate::.ctor
// method line 8
.method public virtual hidebysig newslot
instance default void Invoke (string message, int32 i) runtime
managed
{
// Method begins at RVA 0x0
// Disassembly of native methods is not supported
} // end of method SampleDelegate::Invoke
// method line 9
.method public virtual hidebysig newslot
instance default class [mscorlib]System.IAsyncResult BeginInvoke
(string message, int32 i, class [mscorlib]System.AsyncCallback callback, object
'object') runtime managed
{
// Method begins at RVA 0x0
// Disassembly of native methods is not supported
} // end of method SampleDelegate::BeginInvoke
// method line 10
.method public virtual hidebysig newslot
instance default void EndInvoke (class [mscorlib]System.IAsyncResult
result) runtime managed
{
// Method begins at RVA 0x0
// Disassembly of native methods is not supported
} // end of method SampleDelegate::EndInvoke
} // end of class SampleDelegate
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