[llvm-dev] Need help with code generation

[mats petersson via llvm-dev]

If you plan on calling C runtime library functions, you probably want to do
what I did:
Cheat, and make a libruntime.a (with C functions to do stuff your compiler
can't do natively) and then link that using clang or gcc.

https://github.com/Leporacanthicus/lacsap/blob/master/binary.cpp#L124

At some point, I plan to replace my runtime library with native Pascal
code, at which point I will be able to generate the ELF binary straight
from my compiler without the runtime library linking in the C runtime
library, but that's not happening anytime real soon. Getting the compiler
to compile v5 of Wirth's original Pascal compiler is higher on the list...
:)

--
Mats

On 19 March 2016 at 20:51, James Molloy via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> 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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>
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