[llvm-dev] Need help with code generation

[Bruce Hoult via llvm-dev]

Yes, you shouldn't have any trouble just declaring and using C functions
such as fopen, fclose, puts, fputs, fputc.

You're likely to find that putc is a macro not a function, in which case
you won't be able to use that.

Depending on whether it's important, if you're running on a Unix-like
system then you could save quite a bit of size in your binary by using
open(2), close(2), read(2), write(2) directly, as they're not any harder to
use. But the C standard library is available in more places.

On Sun, Mar 20, 2016 at 1:15 AM, Lorenzo Laneve via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> @james
> Yeah for code generation I figured out that clang doesn't actually use
> llc, and I already started reading its code to see how it works.
> For the ld, there's not an "helper" in the llvm library that calls it, is
> there?
> By the way, I thought about calling ld with things like execl() or
> std::system(), I don't know if it's a good idea, I'm always afraid there
> are better ways than mine!
>
>
> @mats
> Yea, I haven't used C's system calls in my own code yet but if I just have
> to declare the function puts in the IR modules (e.g.: putc) and then link
> against libc, am I right?
> Should I use basic C functions such as putc() and getc(), in my runtime
> library or is there a more efficient way to set up my runtime library?
>
> On Mar 19, 2016, at 9:58 PM, mats petersson <mats at planetcatfish.com>
> wrote:
>
> 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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>
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