[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]

After trying different things, I realized that I should modify the
visibility of the conflicting
variables on the target linked.ll file to hidden, before calling the linker.

This can be easily done by calling llvm-extract with the delete option to
prepare a file to
receive the linked function

llvm-extract-4.0 code03.ll -func main -S -o extracted_main.ll
> lvm-extract-4.0 code03.ll -func main -delete -S -o linked.ll
> llvm-link-4.0 linked.ll -only-needed -override extracted_main.ll -S -o
> linked_main.ll


This works great for a single module compilation.
But what are the effects if I have several modules?

Thanks,
- nico

2017-08-29 17:10 GMT-05:00 Nicolas Agostini <n.b.agostini at gmail.com>:

> 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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