[llvm-dev] Inserting a function with arguments to appendToGlobalCtors

[David Blaikie via llvm-dev]

On Mon, Dec 21, 2020 at 6:16 PM Mohannad Ismail <imohannad at vt.edu> wrote:

> Hi David,
>
> Thank you for your fast reply.
>
> That's a good idea. But the arguments I need are obtained from the IR, or
> in more accurately, from the static analysis I do on the IR. I can't
> get these arguments externally. Are you proposing I create the function
> within the pass? How do I do that?
>

If it's necessary to create the pass you want to, yeah, you could introduce
a function within the transformation pass. (I guess it'd have to be a
module pass, if it adds a function - I'm not 100% sure on that). Same way
you create an IR function at any point - I guess IRBuilder::createFunction
or something like that.


>
> On Mon, Dec 21, 2020 at 8:40 PM David Blaikie <dblaikie at gmail.com> wrote:
>
>> You probably need to create a function that takes no arguments - and have
>> that function then create the arguments and call the
>> functions-taking-arguments you want to run as global ctors. Add the outer
>> no-argument-taking-function to the global ctors list.
>>
>> On Mon, Dec 21, 2020 at 5:28 PM Mohannad Ismail via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> I want to insert a function call that executes first. I figured the way
>>> to do this is to insert to the global constructors with
>>> appendToGlobalCtors() in this way:
>>>
>>> LLVMContext &C = M.getContext();
>>> Function* FInit = Function::Create(FunctionType::get(Type::getVoidTy(C), false), GlobalValue::ExternalLinkage, INITMEMORY, &M);
>>> appendToGlobalCtors(M, FInit, 0);
>>>
>>> This works well if the function has no arguments. But what if the
>>> function I need to insert has arguments that I would like to specify? How
>>> do I create the function to insert into the global constructors? The
>>> function I have returns void. I already know how to use the IRBuilder to
>>> create a function call. But the builder takes the arguments in the
>>> builder.CreateCall(Func, FuncArgs). In general, I need to execute a bunch
>>> of function calls first when I am able to obtain their parameters in the
>>> program.
>>>
>>> Hope I was clear enough. Let me know if this needs more clarification.
>>> Thanks!
>>>
>>>
>>> Best regards,
>>>
>>> Mohannad Ismail
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
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