[llvm-dev] Need help with code generation

[James Molloy via llvm-dev]

Hi Lorenzo,

Clang doesn't call llc; LLVM is compiled into Clang. Clang does call the
system linker though.

Making your compiler generate *object* code is very simple. Making it fixup
that object code and execute it in memory (JIT style) is also simple.
Linking it properly and creating a fixed up ELF file is less simple. For
that, you need to compile to object (using addPassesToEmitFile() - see
llc.cpp) then invoke a linker. Getting that command line right can be quite
difficult.

Rafael, This would be a good usecase for LLD as a library. I heard that
this is is an explicit non-goal, which really surprised me. Is that indeed
the case?

Cheers,

James

On Sat, 19 Mar 2016 at 13:32 Lorenzo Laneve via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'd like to make my compiler independent, just like Clang. Doesn't Clang
> call llc and then system's ld by itself? I don't want my compiler to depend
> by any other program.
> I guess there will be a class in the llvm library that generates the
> object files based on the system's triple and data layout, and then call
> the system's ld?
>
> On Mar 19, 2016, at 11:48 AM, Bruce Hoult <bruce at hoult.org> wrote:
>
> If you've created a .bc or a .ll file then the simplest thing is to just
> give it to clang exactly the same as you would for a .c file. Clang will
> just Do The Right Thing with it.
>
> If you don't want to link, then pass flags such as -c to clang as usual.
>
> e.g.
>
> ---- hello.ll ----
> declare i32 @puts(i8*)
> @str = constant [12 x i8] c"Hello World\00"
>
> define i32 @main() {
>   %1 = call i32 @puts(i8* getelementptr inbounds ([12 x i8]* @str, i64 0,
> i64 0))
>   ret i32 0
> }
> ----------------
>
> $ clang hello.ll -o hello && ./hello
> warning: overriding the module target triple with
> x86_64-apple-macosx10.10.0
> 1 warning generated.
> Hello World
>
>
> On Sat, Mar 19, 2016 at 3:03 AM, Lorenzo Laneve via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I wrote my compiler and now it generates LLVM IR modules. Now i’d like to
>> go ahead and make object file and then executable, just like clang does.
>>
>> What should I have to use to create the object files? and then how do I
>> call the ld? (not llvm-ld, I want my compiler to work like Clang and I read
>> that Clang doesn’t use llvm-ld).
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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