[Mono-dev] Adding a new opcode

[Denis ERCHOFF]

Hi,

I want to add a new opcode ( for educational purpose ) and i have some 
questions.

First i explain what i want to do :

I have a C struct :

struct MyStruct
{
    int MyField;
}

In the managed code, i have a property of type IntPtr ( MyManagedProp ). 
MyManagedProp is setup with a pointer to a MyStruct.

I defined a new opcode "myopcode" in the files opcodes.def. This opcode, 
using a MyStruct pointer, must load the MyField value.

So, in the managed code i am pushing the MyManagedProp on the stack, i 
am calling the myopcode which do some work. After i am calling an 
internal C function taking an int argument.

I am thinking define the myopcode like the OP_STRLEN :

reg: OP_MYOPCODE (reg) {   
    MONO_EMIT_LOAD_MEMBASE_OP (s, tree, OP_LOADI4_MEMBASE, state->reg1,
                   state->left->reg1, G_STRUCT_OFFSET (MyStruct, MyField));
}

1) Because my IntPtr is stored on the managed stack, should i add a pop 
command before the MONO_EMIT_LOAD_MEMBASE_OP ?

2) After MyField value is moved in a reg, i want to add a jit icall 
using this value. Should i add a push command to push it on the stack ?

3) Can i add the the icall directly in the burg file as  :
reg: OP_MYOPCODE (reg) {   
    MONO_EMIT_LOAD_MEMBASE_OP (s, tree, OP_LOADI4_MEMBASE, state->reg1,
                   state->left->reg1, G_STRUCT_OFFSET (MyStruct, MyField));
                    emit_call (cfg, code, MONO_PATCH_INFO_ABS, call->fptr);
}

4) Any comments to explain how mono choose and manage registers are 
welcome :)

Thanks.