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marwayusuf@feng.bu.edu.eg via llvm-dev

2015-Aug-19 22:42 UTC

[llvm-dev] creating a callinst to an external function

Dear All

I'm making an instrumentation pass. The pass is supposed to modify the given
IR in a specefic way. One of the required modifications is to insert a call to a
function at a specific location.

This is the signature of the called function:

      void myclass::foo(Function *f, BasicBlock* b)

This function's prototype is in an foofile.h file in include/llvm

And the function definition is in foofile.cpp file in the MCJIT folder.

and running "make" at this folder works fine and the foofile.cpp is
compiled with MCJIT.cpp and another function in the same file works just fine as
expected.

Not back to the instrumentation pass. How can I insert a callinst to the foo
function in the given IR?

Here is the snippet that inserts the call:

           Type* retTy = Type::getInt32Ty(C);

            FunctionType* FuncTy = FunctionType::get(retTy, false);

            PointerType* PtrToFuncTy = PointerType::get(FuncTy, 0);

            Constant *fun = M->getOrInsertFunction("foo",
Type::getVoidTy(C), PtrToFuncTy, Type::getLabelTy(C), nullptr);

            Function *dofoo = cast<Function>(fun);

            Instruction* dofooCall = CallInst::Create(fun, Args2, "",
bb);


Note: Args2 is an arraylist containing 2 value pointers to a function and a
basicblock, bb is the basicblock to insert the call in.


When I run the pass using op on a given IR, it produces a declaration and a call
correctly like this:

 declaration:       declare void @foo(i32 ()*, label)

 call:                   call void @foo(i32 ()* @main, label %for.cond)

But when I try to run the resulting .ll file using lli, everything explodes!
This the first 2 lines before the stacktrace:

    Can't get register for value!

    UNREACHABLE executed at
/home/marwayusuf/llvm-env/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:1158!



I concluded that the problem is it can't find the foo function. If this is
the problem, how can I create the callinst correctly?




Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.
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marwayusuf@feng.bu.edu.eg via llvm-dev

2015-Sep-02 14:17 UTC

head link

[llvm-dev] creating a callinst to an external function

I tried to remove parameters from the called function "foo". So I got
a different error.

LLVM ERROR: Program used external function 'foo' which could not be
resolved!

Any help?


Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.


________________________________
From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of
marwayusuf at feng.bu.edu.eg via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Thursday, August 20, 2015 12:42 AM
To: llvm-dev at lists.llvm.org
Subject: [llvm-dev] creating a callinst to an external function


Dear All

I'm making an instrumentation pass. The pass is supposed to modify the given
IR in a specefic way. One of the required modifications is to insert a call to a
function at a specific location.

This is the signature of the called function:

      void myclass::foo(Function *f, BasicBlock* b)

This function's prototype is in an foofile.h file in include/llvm

And the function definition is in foofile.cpp file in the MCJIT folder.

and running "make" at this folder works fine and the foofile.cpp is
compiled with MCJIT.cpp and another function in the same file works just fine as
expected.

Not back to the instrumentation pass. How can I insert a callinst to the foo
function in the given IR?

Here is the snippet that inserts the call:

           Type* retTy = Type::getInt32Ty(C);

            FunctionType* FuncTy = FunctionType::get(retTy, false);

            PointerType* PtrToFuncTy = PointerType::get(FuncTy, 0);

            Constant *fun = M->getOrInsertFunction("foo",
Type::getVoidTy(C), PtrToFuncTy, Type::getLabelTy(C), nullptr);

            Function *dofoo = cast<Function>(fun);

            Instruction* dofooCall = CallInst::Create(fun, Args2, "",
bb);


Note: Args2 is an arraylist containing 2 value pointers to a function and a
basicblock, bb is the basicblock to insert the call in.


When I run the pass using op on a given IR, it produces a declaration and a call
correctly like this:

 declaration:       declare void @foo(i32 ()*, label)

 call:                   call void @foo(i32 ()* @main, label %for.cond)

But when I try to run the resulting .ll file using lli, everything explodes!
This the first 2 lines before the stacktrace:

    Can't get register for value!

    UNREACHABLE executed at
/home/marwayusuf/llvm-env/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:1158!



I concluded that the problem is it can't find the foo function. If this is
the problem, how can I create the callinst correctly?




Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.
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mats petersson via llvm-dev

2015-Sep-02 14:36 UTC

head link

[llvm-dev] creating a callinst to an external function

If you look at the computer output of the file that provides the function
`myclass::foo` (-S -emit-llvm if you use clang), you should see that the
name of the function (probably) isn't `foo`. You need to precisely match
the name between the caller and the actual function.

--
Mats



On 2 September 2015 at 15:17, marwayusuf at feng.bu.edu.eg via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I tried to remove parameters from the called function "foo". So I
got a
> different error.
>
> LLVM ERROR: Program used external function 'foo' which could not be
> resolved!
>
> Any help?
>
>
> Regards,
> Marwa Yusuf
> Teaching Assistant - Computer Engineering Department
> Faculty of Engineering - Benha University
> E-JUST PhD Student
> Computer Science & Engineering Dept.
>
>
> ------------------------------
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of
> marwayusuf at feng.bu.edu.eg via llvm-dev <llvm-dev at
lists.llvm.org>
> *Sent:* Thursday, August 20, 2015 12:42 AM
> *To:* llvm-dev at lists.llvm.org
> *Subject:* [llvm-dev] creating a callinst to an external function
>
>
> Dear All
>
> I'm making an instrumentation pass. The pass is supposed to modify the
> given IR in a specefic way. One of the required modifications is to insert
> a call to a function at a specific location.
>
> This is the signature of the called function:
>
>       void myclass::foo(Function *f, BasicBlock* b)
>
> This function's prototype is in an foofile.h file in include/llvm
>
> And the function definition is in foofile.cpp file in the MCJIT folder.
>
> and running "make" at this folder works fine and the foofile.cpp
is
> compiled with MCJIT.cpp and another function in the same file works just
> fine as expected.
>
> Not back to the instrumentation pass. How can I insert a callinst to the
> foo function in the given IR?
>
> Here is the snippet that inserts the call:
>
>            Type* retTy = Type::getInt32Ty(C);
>
>             FunctionType* FuncTy = FunctionType::get(retTy, false);
>
>             PointerType* PtrToFuncTy = PointerType::get(FuncTy, 0);
>
>             Constant *fun = M->getOrInsertFunction("foo",
> Type::getVoidTy(C), PtrToFuncTy, Type::getLabelTy(C), nullptr);
>
>             Function *dofoo = cast<Function>(fun);
>
>             Instruction* dofooCall = CallInst::Create(fun, Args2,
"", bb);
>
>
> Note: Args2 is an arraylist containing 2 value pointers to a function and
> a basicblock, bb is the basicblock to insert the call in.
>
>
> When I run the pass using op on a given IR, it produces a declaration and
> a call correctly like this:
>
>  declaration:       declare void @foo(i32 ()*, label)
>
>  call:                   call void @foo(i32 ()* @main, label %for.cond)
>
> But when I try to run the resulting .ll file using lli, everything
> explodes! This the first 2 lines before the stacktrace:
>
>     Can't get register for value!
>
>     UNREACHABLE executed at
>
/home/marwayusuf/llvm-env/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:1158!
>
>
>
> I concluded that the problem is it can't find the foo function. If this
is
> the problem, how can I create the callinst correctly?
>
>
>
>
> Regards,
> Marwa Yusuf
> Teaching Assistant - Computer Engineering Department
> Faculty of Engineering - Benha University
> E-JUST PhD Student
> Computer Science & Engineering Dept.
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Tim Northover via llvm-dev

2015-Sep-02 14:37 UTC

head link

[llvm-dev] creating a callinst to an external function

On 19 August 2015 at 23:42, marwayusuf at feng.bu.edu.eg via llvm-dev
<llvm-dev at lists.llvm.org> wrote:>       void myclass::foo(Function *f, BasicBlock* b)
> [...]
>  call:                   call void @foo(i32 ()* @main, label %for.cond)
The problem here is that a "Function *" isn't simply a function
pointer, or even a function pointer at all. It's a compile-time
representation of some function. Similar comments apply to BasicBlock.
I'm quite surprised it even reached SelectionDAGBuilder before blowing
up.

That information is not normally available at runtime, though in
principle you could get one in there if you were JITing. If you know
where the Function lives when you're generating the IR (and can
guarantee it won't move) you could aim for something like:

   call void @foo(i8* inttoptr(i64 0x123450 to i8*), inttoptr(i64 ...))

Something like:

    Function *Main = ...;
    Value *Arg =
Constant::CreateIntToPtr(reinterpret_cast<uint64_t>(Main));

I.e. instead of using Main as a Value in the call expression,
completely hide the fact that it's an LLVM object from the compiler
and pass it in as an opaque integer. Also, don't forget the "this"
pointer if "foo" is not a static method.

Cheers.

Tim.

marwayusuf@feng.bu.edu.eg via llvm-dev

2015-Sep-09 13:30 UTC

head link

[llvm-dev] creating a callinst to an external function

Thanks a million for help. I got the general idea but I could not manage to
implement it.
I understood that I need to create IntToPtrInst that is supposed to convert an
integer (that represents the function address)  back to a function pointer at
the callee side. But I have some questions:
How I get this integer value at the first place?
I tried something like:
     Value *Arg1 = new IntToPtrInst(reinterpret_cast<uint64_t>(F),
F->getType());
It gave me this compilation error:
    error: no matching function for call to
‘llvm::IntToPtrInst::IntToPtrInst(uint64_t, llvm::PointerType*)’
and
     Value *Arg1 = new IntToPtrInst(F, F->getType());
It gave me this runtime error (during applying the pass):
     llvm::IntToPtrInst::IntToPtrInst(llvm::Value*, llvm::Type*, const
llvm::Twine&, llvm::Instruction*): Assertion `castIsValid(getOpcode(), S,
Ty) && "Illegal IntToPtr"' failed.


Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.

________________________________________
From: Tim Northover <t.p.northover at gmail.com>
Sent: Wednesday, September 2, 2015 4:37 PM
To: marwayusuf at feng.bu.edu.eg
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] creating a callinst to an external function

On 19 August 2015 at 23:42, marwayusuf at feng.bu.edu.eg via llvm-dev
<llvm-dev at lists.llvm.org> wrote:>       void myclass::foo(Function *f, BasicBlock* b)
> [...]
>  call:                   call void @foo(i32 ()* @main, label %for.cond)
The problem here is that a "Function *" isn't simply a function
pointer, or even a function pointer at all. It's a compile-time
representation of some function. Similar comments apply to BasicBlock.
I'm quite surprised it even reached SelectionDAGBuilder before blowing
up.

That information is not normally available at runtime, though in
principle you could get one in there if you were JITing. If you know
where the Function lives when you're generating the IR (and can
guarantee it won't move) you could aim for something like:

   call void @foo(i8* inttoptr(i64 0x123450 to i8*), inttoptr(i64 ...))

Something like:

    Function *Main = ...;
    Value *Arg =
Constant::CreateIntToPtr(reinterpret_cast<uint64_t>(Main));

I.e. instead of using Main as a Value in the call expression,
completely hide the fact that it's an LLVM object from the compiler
and pass it in as an opaque integer. Also, don't forget the "this"
pointer if "foo" is not a static method.

Cheers.

Tim.

marwayusuf@feng.bu.edu.eg via llvm-dev

2015-Sep-09 14:21 UTC

head link

[llvm-dev] creating a callinst to an external function

Thanks a million for your help.
foo function is properly called now, if I pass no parameters. However, it stops
if I try to pass an llvm Function as a prameter.
The problem arises if I try to perform any operation (like getName) on this
passed function. It gives me a segmentation fault. I checked and found it's
not NULL.
I understood from your answer that I should convert the function pointer into an
integer that represents its address and then convert it back into a pointer in
the instrumented IR. However, I could not get how exactly to do that. I tried
some code but with no luck. If you please explain the idea more, I'll
appreciate. Thanks in advance.

Regards,
Marwa Yusuf
Teaching Assistant - Computer Engineering Department
Faculty of Engineering - Benha University
E-JUST PhD Student
Computer Science & Engineering Dept.

________________________________________
From: Tim Northover <t.p.northover at gmail.com>
Sent: Wednesday, September 2, 2015 4:37 PM
To: marwayusuf at feng.bu.edu.eg
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] creating a callinst to an external function

On 19 August 2015 at 23:42, marwayusuf at feng.bu.edu.eg via llvm-dev
<llvm-dev at lists.llvm.org> wrote:>       void myclass::foo(Function *f, BasicBlock* b)
> [...]
>  call:                   call void @foo(i32 ()* @main, label %for.cond)
The problem here is that a "Function *" isn't simply a function
pointer, or even a function pointer at all. It's a compile-time
representation of some function. Similar comments apply to BasicBlock.
I'm quite surprised it even reached SelectionDAGBuilder before blowing
up.

That information is not normally available at runtime, though in
principle you could get one in there if you were JITing. If you know
where the Function lives when you're generating the IR (and can
guarantee it won't move) you could aim for something like:

   call void @foo(i8* inttoptr(i64 0x123450 to i8*), inttoptr(i64 ...))

Something like:

    Function *Main = ...;
    Value *Arg =
Constant::CreateIntToPtr(reinterpret_cast<uint64_t>(Main));

I.e. instead of using Main as a Value in the call expression,
completely hide the fact that it's an LLVM object from the compiler
and pass it in as an opaque integer. Also, don't forget the "this"
pointer if "foo" is not a static method.

Cheers.

Tim.

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