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

[UE US via llvm-dev]

I'm a bit rusty so forgive me if I'm not making sense, but wouldn't you
want to extract the string literals along with the function in this case
and re-link both later?

Gordon Keiser,
Software Delousing Engineer

On Wed, Aug 30, 2017 at 2:53 PM, Nicolas Agostini via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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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