[PATCH] Expose MCInst in C Disassembler API

[Filip Pizlo]

It’s great to see more things being exposed in the C API, and I think that this is generally the right direction.

Some comments:

>  size_t LLVMDisasmInstruction(LLVMDisasmContextRef DC, uint8_t *Bytes,
>                               uint64_t BytesSize, uint64_t PC,
> +                             LLVMMCInstRef* Inst,
>                               char *OutString, size_t OutStringSize);

Adding a new parameter to this function will break previous callers to this function.  The C API should be stable.  Hence, I think that you need to add a new version of LLVMDisasmInstruction().

> +/*===-- llvm-c/MCInst.h - Disassembler Public C Interface ---*- C -*-===*\

It feels like maybe this should just go into an existing file, rather than adding a new file.  It seems like the current convention in the C API is to have a smaller number of more populous headers.

> +typedef struct {
> +  LLVMMCOperandType Kind;
> +  union {
> +    unsigned RegVal;
> +    int64_t ImmVal;
> +    double FPImmVal;
> +    LLVMMCInstRef InstVal;
> +  };
> +} LLVMMCOperand;

I’m worried that defining the struct in this way will result in compatibility hassles in the future.  Can we be sure that we won’t ever change the types of any of these things?

I would feel better if operands were represented as an OperandRef with functions to get their contents.  This would allow for forward/backward ABI compatibility if new fields were added or existing fields had their types changed.

-Filip



> On Jun 20, 2014, at 12:08 PM, Matthew Maurer <maurer+llvmphabricator at matthewmaurer.org> wrote:
> 
> Partially expose the MCInst struct from the C Disassembler API to allow mechanized examination of opcodes and arguments.
> 
> http://reviews.llvm.org/D4236
> 
> Files:
>  include/llvm-c/Disassembler.h
>  include/llvm-c/MCInst.h
>  lib/MC/MCDisassembler/Disassembler.cpp
>  lib/MC/MCInst.cpp
>  tools/llvm-c-test/disassemble.c
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