[lldb-dev] [LLVMdev] Reusing LLVM Mips instruction info in lldb

[Greg Clayton]

We should really try to get this header file generated if possible. 
> On Feb 24, 2015, at 1:19 PM, Keno Fischer <kfischer at college.harvard.edu> wrote:
> 
> The basic problem is the following. In, LLDB I get an instruction from the target and then I ask the LLVM disassembler to disassemble it for me. Depending on the instruction and what the arguments are, I can now construct an unwind plan. I get an MCInst back from the disassembler, so what I want to do is sth like:
> 
> if (Inst.getOpcode() == Mips::Addiu || Inst.getOpcode() == Mips::DAddiu) {
> // This is an addiu instruction, look at the registers and construct the unwind plan
> }
> 
> but that enum is the one that's tablegen'd. I guess a possible interface would be to ask for the opcode of an instruction by name? Seems somewhat ugly though.
> 
> 
> On Tue, Feb 24, 2015 at 4:09 PM, Eric Christopher <echristo at gmail.com> wrote:
> 
> 
> On Tue Feb 24 2015 at 1:03:43 PM Keno Fischer <kfischer at college.harvard.edu> wrote:
> Hello everyone,
> 
> in http://reviews.llvm.org/D7696 bhushan added a mips64 UnwindAssembly plugin (a plugin that looks at assembly code to find out how to unwind the stack frame). Since I was about to write such a plugin (though for mips32) myself, I used it as a starting point for a slightly different implementation [1], replacing hard coded instruction encodings by calls to the LLVM disassembler. This works great, except that the necessary header that defines the enum to interpret the opcode in MCInst is generated by llvm during the build process using tablegen and is hence not a public header. What is the best solution to be able to use this information from lldb (which needs to be able to build against a prebuilt copy of LLVM)? Would it make sense to move the appropriate .td to llvm/include/Target/Mips, so lldb could re-tablegen it and obtain the same header (I assume tablegening is deterministic?)?
> 
> Ugh no. (Though yes, it is deterministic afaik).
>  
> Does anybody see any other good solutions?
> 
> 
> Develop an interface that works and have lldb use that? Might need to change things to have certain bits be made public if necessary, but I'd want more details there.
> 
> -eric 
> 
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