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by Const-me 1933 days ago
Processors need addresses of things. Look at the following code https://godbolt.org/z/PYEqKn note the function uses another symbol, “func.counter”.

Shared libraries include relocation tables https://en.wikipedia.org/wiki/Relocation_%28computing%29 with all code locations which needs patching. That’s how the OSes can load them into arbitrary locations in memory and the code will still work.
1 comments
jcelerier 1933 days ago
... yes ? https://github.com/weliveindetail/JitFromScratch
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Const-me 1933 days ago
Interesting, I didn’t know llvm is that flexible.

Still, LLVM is a huge dependency to redistribute. And probably has many points of failure. For instance, I expect you gonna need to watch for INCLUDE and PATH environment variables when using that thing.

In .NET everything is in the standard library. The generated code is even platform-independent, for no additional overhead. Here’s couple non-trivial examples: https://github.com/Const-me/ComLightInterop/blob/master/ComL... https://github.com/Const-me/ComLightInterop/blob/master/ComL...

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SubjectToChange 1932 days ago
> Still, LLVM is a huge dependency to redistribute.

But .NET isn't?

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Const-me 1932 days ago
> But .NET isn't?

Indeed.

.NET runtime takes about 30 MB, or 50 MB if you're on Windows and need desktop components. Links there: https://dotnet.microsoft.com/download/dotnet/5.0

clang+llvm package takes 300-400 MB, that's almost an order of magnitude difference: https://github.com/llvm/llvm-project/releases/tag/llvmorg-11...

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jcelerier 1932 days ago
> clang+llvm package takes 300-400 MB, that's almost an order of magnitude difference

I ship a statically compiled llvm + clang with my software and it does not add 300-400 mb to the binary at all, only something like 20-30 mb.

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Const-me 1932 days ago
If you’re willing to compile, ship and support custom builds of .NET runtime, gonna be less than 20-30 MB.

coreclr.dll (the runtime) is 4.9 MB, clrjit.dll (JIT compiler) is 1.3 MB. The rest is mostly standard libraries, the largest piece of that is System.Private.CoreLib.dll at 9 MB. The numbers are for Win64 version of .NET 5.0.2.

Another thing, for .NET apps the runtime is required anyway, the overhead for runtime code generation is zero.

For C++ apps, llvm + clang (or an equivalent) is only needed on developer’s computers, not something you’d normally ship.

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