[llvm-dev] Is the flow "llvm-extract -> llvm-link -> clang++ " supposed to be used in this way? To Extract and Re-insert functions?

[Nicolas Agostini via llvm-dev]

Hi all,
First post to the list, I hope you can help or guide me on this task.

I am involved in a project that requires to re-link extracted and edited IR
code

Thus I want to know if these tools can be used in this way?

clang++-4.0 code03.cpp -emit-llvm -S -o code03.ll
llvm-extract-4.0 code03.ll -func main -S -o extracted_main.ll
llvm-link-4.0 code03.ll -only-needed -override extracted_main.ll -S -o
linked_main.ll
clang++-4.0 linked_main.ll -o main.out


where code03.cpp is:

#include <iostream>
> using namespace std;
> int main()
> {
>   cout << "First Message\n ";
>   cout << "Second Message\n ";
>   cout << "Third Message\n ";
>   return 0;
> }



I have been trying to extract a function's llvm IR, modify it preserving
its signature (or not), and re-insert this function back to the original IR
file, however I am getting an error during the compilation step (
clang++-4.0 linked_main.ll -o main.out ):

main.ll:(.text+0x14): undefined reference to `.str'
> main.ll:(.text+0x34): undefined reference to `.str.1'
> main.ll:(.text+0x51): undefined reference to `.str.2'


 and linked_main.ll file has this section:

@.str.4 = private unnamed_addr constant [16 x i8] c"First Message\0A \00",
> align 1
> @.str.1.6 = private unnamed_addr constant [17 x i8] c"Second Message\0A
> \00", align 1
> @.str.2.8 = private unnamed_addr constant [16 x i8] c"Third Message\0A
> \00", align 1
> @.str = external hidden unnamed_addr constant [16 x i8], align 1
> @.str.1 = external hidden unnamed_addr constant [17 x i8], align 1
> @.str.2 = external hidden unnamed_addr constant [16 x i8], align 1



But the function does not use the correct versions of the strings as the
linked "extracted_main" keeps making calls to .str, .str.1, .str.2? Am I
not supposed to do it this way?

Thank you in advance

- nico
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