[llvm-dev] Need help with code generation

[Rui Ueyama via llvm-dev]

We had a long discussion recently and the decision was made so that we can
go ahead. It is not a good idea to discuss that again. At least it is too
soon.

I'd recommend to use lld's link() function if input is guaranteed to be
consistent (such as outputs of clang). Otherwise, please use fork.

On Mon, Mar 21, 2016 at 8:10 PM, James Molloy <james at jamesmolloy.co.uk>
wrote:

> Well sure, it's unlikely, but how many consumers can make that sort of
> guarantee? And if a consumer can't guarantee the integrity of the ELF file
> they have no choice but not to use LLD, or to fork before using it.
>
> On Mon, 21 Mar 2016 at 19:08 Rui Ueyama <ruiu at google.com> wrote:
>
>> On Mon, Mar 21, 2016 at 8:04 PM, James Molloy <james at jamesmolloy.co.uk>
>> wrote:
>>
>>> > A corrupted file could cause a fatal error or SEGV.
>>>
>>> Uhhh, that's not particularly useful.
>>>
>>
>> "Corrupted" means really corrupted, like ELF header is broken. Is this
>> really the case?
>>
>>
>>> On Mon, 21 Mar 2016 at 19:02 Rui Ueyama <ruiu at google.com> wrote:
>>>
>>>> On Sat, Mar 19, 2016 at 9:51 PM, 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?
>>>>>
>>>>
>>>> You can use LLD as a library.
>>>>
>>>> https://github.com/llvm-mirror/lld/blob/master/docs/NewLLD.rst#the-elf-linker-as-a-library
>>>>
>>>>
>>>>> 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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>>>>>> llvm-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>>
>>>>>
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