Add function signature reconstruction for Issue #14

[kami922]

• Parse FuncType metadata to extract input/output parameter types (including variadic flag).
• Build C-style function pointer typedefs and emit them in CReconstructed for Func kinds.
• Represent multiple returns by commenting them in the typedef (C still single-return).
• Add IDA script scaffolding to ingest function types (signature application is intentionally left as future work).
• JSON now carries function signatures instead of opaque void* for functions.

[kami922]

@stevemk14ebr Hello

based on your review, here is the remaining checklist for the next commit. let me know if I missed anything.

• Implement[apply_function_type in the IDA script to actually apply reconstructed signatures to funcs/args/locals.
• Improve multiple-return handling (currently commented in typedef; consider struct/tuple).
• Add small Go fixtures/tests to assert CReconstructed for funcs and an IDA import smoke test.

[stevemk14ebr]

I like where this is going! We can do better with the arg type and return type parsing though. Checkout this case

.rodata:00000000005B1F40 RTYPE_funcunsafe_Pointer_comma__unsafe_Pointer_bool RTYPE <8, 8, 6BB69B10h, TFLAG_EXTRASTAR, 8, 8, \
.rodata:00000000005B1F40                                         ; DATA XREF: .rodata:00000000005C7F08↓o
.rodata:00000000005B1F40                                         ; .rodata:00000000005C7F18↓o ...
.rodata:00000000005B1F40                        KIND_FUNC or KIND_DIRECTIFACE, 0, offset runtime_gcbits__ptr_, \
.rodata:00000000005B1F40                        offset byte_5A2644 - offset type__ptr_, 0>
.rodata:00000000005B1F70                 FUNC_TYPE <2, 1>
.rodata:00000000005B1F74                 align 8
.rodata:00000000005B1F78                 dq offset RTYPE_unsafe_Pointer
.rodata:00000000005B1F80                 dq offset RTYPE_unsafe_Pointer
.rodata:00000000005B1F88                 dq offset RTYPE_bool
.rodata:00000000005B1F90                 align 20h

This function takes 2 inputs, has 1 output, and the types of all 3 are present. Our reconstructed typedef is

{
    VA: 5971776, 
    Str: "func(unsafe.Pointer, unsafe.Pointer) bool", 
    CStr: "func(unsafe_Pointer,_unsafe_Pointer)_bool_funcptr", 
    Kind: "Func", 
    Reconstructed: "", 
    CReconstructed: "typedef void* (*func(unsafe_Pointer,_unsafe_Pointer)_bool_funcptr)(void*, void*)", 
    baseSize: 48, 
    kindEnum: Func (19), 
    flags: tflagExtraStar (2)
}

I'd expect the CStr to be bool (unsafe_Pointer,_unsafe_Pointer), the Reconstructed to be type funcunsafe_Pointer_comma__unsafe_Pointer_bool(unsafe.Pointer, unsafe.Pointer) bool or something similar. The CReconstructed is wrong, it should be something similar to typedef bool (*func_unsafe_Pointer__unsafe_Pointer_bool_funcptr)(unsafe_Pointer, unsafe_Pointer). In general we try to match the naming scheme of IDA, Reconstructed tries to use Go syntax, and CReconstructed tries to use C or C++ syntax.

So there's some formatting issues with the reconstruction, but the raw parsing logic seems mostly working! I agree with all the follow on work points, especially about tests.

For multiple return values we can use either structures or tuples, the project uses structures now, but IDA recently added tuples for Go so lets prefer those for this function type work. https://hex-rays.com/blog/stop-guessing-and-start-going

Actually applying these signatures via IDA scripting can be quite tricky since the types recursively depend on other types. I am completely ok with not having the IDA script implemented for now. I care most about reasonable and correct symbol recovery. We can do the IDA script work later.