RenderScript/RenderScriptRuntime/RenderScriptx86ABIFixups.cpp

//===-- x86ABIFixups.cpp ----------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

// C Includes
// C++ Includes
#include <set>

// Other libraries and framework includes
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IRReader/IRReader.h"
#include "llvm/Pass.h"

// Project includes
#include "lldb/Core/Log.h"
#include "lldb/Target/Process.h"

using namespace lldb_private;
namespace
{

bool
isRSAPICall(llvm::Module &module, llvm::CallInst *call_inst)
{
    // TODO get the list of renderscript modules from lldb and check if
    // this llvm::Module calls into any of them.
    (void)module;
    const auto func_name = call_inst->getCalledFunction()->getName();
    if (func_name.startswith("llvm") || func_name.startswith("lldb"))
        return false;

    if (call_inst->getCalledFunction()->isIntrinsic())
        return false;

    return true;
}

bool
isRSLargeReturnCall(llvm::Module &module, llvm::CallInst *call_inst)
{
    // i686 and x86_64 returns for large vectors in the RenderScript API are not handled as normal
    // register pairs, but as a hidden sret type. This is not reflected in the debug info or mangled
    // symbol name, and the android ABI for x86 and x86_64, (as well as the emulators) specifies there is
    // no AVX, so bcc generates an sret function because we cannot natively return 256 bit vectors.
    // This function simply checks whether a function has a > 128bit return type. It is perhaps an
    // unreliable heuristic, and relies on bcc not generating AVX code, so if the android ABI one day
    // provides for AVX, this function may go out of fashion.
    (void)module;
    if (!call_inst || !call_inst->getCalledFunction())
        return false;

    return call_inst->getCalledFunction()->getReturnType()->getPrimitiveSizeInBits() > 128;
}

bool
isRSAllocationPtrTy(const llvm::Type *type)
{
    if (!type->isPointerTy())
        return false;
    auto ptr_type = type->getPointerElementType();

    return ptr_type->isStructTy() && ptr_type->getStructName().startswith("struct.rs_allocation");
}

bool
isRSAllocationTyCallSite(llvm::Module &module, llvm::CallInst *call_inst)
{
    (void)module;
    if (!call_inst->hasByValArgument())
        return false;
    for (const auto &param : call_inst->operand_values())
        if (isRSAllocationPtrTy(param->getType()))
            return true;
    return false;
}

llvm::FunctionType *
cloneToStructRetFnTy(llvm::CallInst *call_inst)
{
    // on x86 StructReturn functions return a pointer to the return value, rather than the return
    // value itself [ref](http://www.agner.org/optimize/calling_conventions.pdf section 6).
    // We create a return type by getting the pointer type of the old return type, and inserting a new
    // initial argument of pointer type of the original return type.
    Log *log(GetLogIfAnyCategoriesSet(LIBLLDB_LOG_LANGUAGE | LIBLLDB_LOG_EXPRESSIONS));

    assert(call_inst && "no CallInst");
    llvm::Function *orig = call_inst->getCalledFunction();
    assert(orig && "CallInst has no called function");
    llvm::FunctionType *orig_type = orig->getFunctionType();
    auto name = orig->getName();
    if (log)
        log->Printf("%s - cloning to StructRet function for '%s'", __FUNCTION__, name.str().c_str());

    unsigned num_params = orig_type->getNumParams();
    std::vector<llvm::Type *> new_params{num_params + 1, nullptr};
    std::vector<llvm::Type *> params{orig_type->param_begin(), orig_type->param_end()};

    // This may not work if the function is somehow declared void as llvm is strongly typed
    // and represents void* with i8*
    assert(!orig_type->getReturnType()->isVoidTy() && "Cannot add StructRet attribute to void function");
    llvm::PointerType *return_type_ptr_type = llvm::PointerType::getUnqual(orig->getReturnType());
    assert(return_type_ptr_type && "failed to get function return type PointerType");
    if (!return_type_ptr_type)
        return nullptr;

    if (log)
        log->Printf("%s - return type pointer type for StructRet clone @ '0x%p':\n", __FUNCTION__,
                    (void *)return_type_ptr_type);
    // put the the sret pointer argument in place at the beginning of the argument list.
    params.emplace(params.begin(), return_type_ptr_type);
    assert(params.size() == num_params + 1);
    return llvm::FunctionType::get(return_type_ptr_type, params, orig->isVarArg());
}

bool
findRSCallSites(llvm::Module &module, std::set<llvm::CallInst *> &rs_callsites,
                bool (*predicate)(llvm::Module &, llvm::CallInst *))
{
    bool found = false;

    for (auto &func : module.getFunctionList())
        for (auto &block : func.getBasicBlockList())
            for (auto &inst : block)
            {
                llvm::CallInst *call_inst = llvm::dyn_cast_or_null<llvm::CallInst>(&inst);
                if (!call_inst || !call_inst->getCalledFunction())
                    // This is not the call-site you are looking for...
                    continue;
                if (isRSAPICall(module, call_inst) && predicate(module, call_inst))
                {
                    rs_callsites.insert(call_inst);
                    found = true;
                }
            }
    return found;
}

bool
fixupX86StructRetCalls(llvm::Module &module)
{
    bool changed = false;
    // changing a basic block while iterating over it seems to have some undefined behaviour
    // going on so we find all RS callsites first, then fix them up after consuming
    // the iterator.
    std::set<llvm::CallInst *> rs_callsites;
    if (!findRSCallSites(module, rs_callsites, isRSLargeReturnCall))
        return false;

    for (auto call_inst : rs_callsites)
    {
        llvm::FunctionType *new_func_type = cloneToStructRetFnTy(call_inst);
        assert(new_func_type && "failed to clone functionType for Renderscript ABI fixup");

        llvm::CallSite call_site(call_inst);
        llvm::Function *func = call_inst->getCalledFunction();
        assert(func && "cannot resolve function in RenderScriptRuntime");
        // Copy the original call arguments
        std::vector<llvm::Value *> new_call_args(call_site.arg_begin(), call_site.arg_end());

        // Allocate enough space to store the return value of the original function
        // we pass a pointer to this allocation as the StructRet param, and then copy its
        // value into the lldb return value
        llvm::AllocaInst *return_value_alloc =
            new llvm::AllocaInst(func->getReturnType(), "var_vector_return_alloc", call_inst);
        // use the new allocation as the new first argument
        new_call_args.emplace(new_call_args.begin(), llvm::cast<llvm::Value>(return_value_alloc));
        llvm::PointerType *new_func_ptr_type = llvm::PointerType::get(new_func_type, 0);
        // Create the type cast from the old function type to the new one
        llvm::Constant *new_func_cast =
            llvm::ConstantExpr::getCast(llvm::Instruction::BitCast, func, new_func_ptr_type);
        // create an allocation for a new function pointer
        llvm::AllocaInst *new_func_ptr = new llvm::AllocaInst(new_func_ptr_type, "new_func_ptr", call_inst);
        // store the new_func_cast to the newly allocated space
        (void)new llvm::StoreInst(new_func_cast, new_func_ptr, "new_func_ptr_load_cast", call_inst);
        // load the new function address ready for a jump
        llvm::LoadInst *new_func_addr_load = new llvm::LoadInst(new_func_ptr, "load_func_pointer", call_inst);
        // and create a callinstruction from it
        llvm::CallInst *new_call_inst =
            llvm::CallInst::Create(new_func_addr_load, new_call_args, "new_func_call", call_inst);
        new_call_inst->setCallingConv(call_inst->getCallingConv());
        new_call_inst->setTailCall(call_inst->isTailCall());
        llvm::LoadInst *lldb_save_result_address = new llvm::LoadInst(return_value_alloc, "save_return_val", call_inst);

        // Now remove the old broken call
        call_inst->replaceAllUsesWith(lldb_save_result_address);
        call_inst->eraseFromParent();
        changed = true;
    }
    return changed;
}

bool
fixupRSAllocationStructByValCalls(llvm::Module &module)
{
    // On x86_64, calls to functions in the RS runtime that take an `rs_allocation` type argument
    // are actually handled as by-ref params by bcc, but appear to be passed by value by lldb (the callsite all use
    // `struct byval`).
    // On x86_64 Linux, struct arguments are transferred in registers if the struct size is no bigger than
    // 128bits [ref](http://www.agner.org/optimize/calling_conventions.pdf) section 7.1 "Passing and returning objects"
    // otherwise passed on the stack.
    // an object of type `rs_allocation` is actually 256bits, so should be passed on the stack. However, code generated
    // by bcc actually treats formal params of type `rs_allocation` as `rs_allocation *` so we need to convert the
    // calling convention to pass by reference, and remove any hint of byval from formal parameters.
    bool changed = false;
    std::set<llvm::CallInst *> rs_callsites;
    if (!findRSCallSites(module, rs_callsites, isRSAllocationTyCallSite))
        return false;

    std::set<llvm::Function *> rs_functions;

    // for all call instructions
    for (auto call_inst : rs_callsites)
    {
        // add the called function to a set so that we can strip its byval attributes in another pass
        rs_functions.insert(call_inst->getCalledFunction());

        // get the function attributes
        llvm::AttributeSet call_attribs = call_inst->getAttributes();

        // iterate over the argument attributes
        for (size_t i = 1; i <= call_attribs.getNumSlots(); ++i)
        {
            // if this argument is passed by val
            if (call_attribs.hasAttribute(i, llvm::Attribute::ByVal))
            {
                // strip away the byval attribute
                call_inst->removeAttribute(i, llvm::Attribute::get(module.getContext(), llvm::Attribute::ByVal));
                changed = true;
            }
        }
    }

    llvm::AttributeSet attr_byval = llvm::AttributeSet::get(module.getContext(), 1u, llvm::Attribute::ByVal);

    // for all called function decls
    for (auto func : rs_functions)
    {
        // inspect all of the arguments in the call
        llvm::SymbolTableList<llvm::Argument> &argList = func->getArgumentList();
        for (auto &arg : argList)
        {
            if (arg.hasByValAttr())
            {
                arg.removeAttr(attr_byval);
                changed = true;
            }
        }
    }
    return changed;
}
} // end anonymous namespace

namespace lldb_private
{
namespace lldb_renderscript
{

bool
fixupX86FunctionCalls(llvm::Module &module)
{
    return fixupX86StructRetCalls(module);
}

bool
fixupX86_64FunctionCalls(llvm::Module &module)
{
    bool changed = false;
    changed |= fixupX86StructRetCalls(module);
    changed |= fixupRSAllocationStructByValCalls(module);
    return changed;
}

} // end namespace lldb_renderscript
} // end namespace lldb_private