Roc platform host shim

[lukewilliamboswell]

Added support for multiple entrypoints in Roc platforms, allowing platforms to expose multiple functions that can be called by the host (e.g., init!, render!, update!).

Key Changes in this PR

1. New Platform Header provides to decouple host entrypoint symbol names

• Updated platform header parsing to support provides { init!: "init_entrypoint", update!: "update_entrypoint" } syntax
• Changed from [] (array) to {} (record) for platform provides

2. Multi-Entrypoint Extraction -- temporary implementations until we can use BuildEnv

• Added extractEntrypointsFromPlatform to parse platform provides and extract function names
• Added extractPlatformSpecFromApp for to extract from app headers

3. Added exports field in ModuleEnv to track the exported definitions for an app module

4. Platform Host Shim Generation

• New platform_host_shim.zig which generates an LLVM bitcode shim that translate between the host's entrypoints and the pre-built interpreter's single entrypoint.
• New builder.zig module for roc cli to compiling LLVM bitcode to object file
• Added LLVM target support

6. Shared Memory Layout

• New Header Structure:

 struct {
     parent_base_addr: u64,
     entry_count: u32,
     _padding: u32,
     def_indices_offset: u64,
     module_env_offset: u64,
 }

• Multi-entrypoint dispatch: entry_idx -> def_idx -> expr_idx
• Persistent state: Global variables to maintain shared memory allocator and ModuleEnv across calls

7. Build System Updates

• Removed -Dllvm build flag (LLVM now included by default)
• Added ZigLLVMInitializeAllTargets() function to zig_llvm wrapper

8. Updated Test Platforms

• Also upgraded the int platform to demonstrate multi-entrypoint functionality.

18:36:06 ~/Documents/GitHub/roc roc-shim $ zig build roc -Doptimize=ReleaseSafe && ./zig-out/bin/roc --no-cache test/int/app.roc
Generated numbers: a = 98, b = 61

=== Testing addInts (entry_idx = 0) ===
Expected add result: 159
Roc computed add: 159
SUCCESS: addInts results match!

=== Testing multiplyInts (entry_idx = 1) ===
Expected multiply result: 5978
Roc computed multiply: 5978
SUCCESS: multiplyInts results match!

=== FINAL RESULT ===
ALL TESTS PASSED: Both entrypoints work correctly!

[lukewilliamboswell]

removed -Dllvm -- this does increase the compilation times if you are doing things that doesn't need it like running snapshots, or unit tests... I feel it is simpler to default to having it. Maybe we have a flag -Dno-llvm if we still want slimmer builds for other things... or we could probably change the build script to not build llvm if we are just building the snapshots etc.

[Anton-4]

@lukewilliamboswell Claude fixed "Run Test Platforms (Unix)" but I'm not sure if the fix is in line with what you had in mind:

Segmentation Fault Fix Report

Summary

The segmentation fault was caused by a target ABI mismatch between:

1. LLVM compilation: Used x86_64-unknown-linux-musl target (native detection)
2. Linking: Forced GNU ABI (x86_64-unknown-linux-gnu) for str platforms
3. Embedded shim library: Compiled with musl ABI

This created an ABI incompatibility where the generated platform shim expected GNU calling conventions but the embedded roc interpreter shim used musl conventions, resulting in a jump to address 0x0.

The Fix

I modified the code in /home/username/gitrepos/roc2/roc/src/cli/main.zig to make str platforms use musl static linking consistently instead of forcing GNU dynamic linking:

Changes Made

1. Platform shim generation: Uses native target (musl)
2. Str platform linking: Changed from .gnu to .musl target ABI
3. CRT files: Uses the same musl vendored files as int platform (test/int/platform/targets/x64musl/)

Result

The fix ensures both LLVM compilation and linking use the same ABI (x86_64-unknown-linux-musl with musl static linking), eliminating the mismatch that caused the segfault.

[Anton-4]

I'm going to check out this flaky CI issue:

/home/runner/work/roc/roc/build.zig.zon:56:20: error: unable to discover remote git server capabilities: EndOfStream
            .url = "git+https://github.com/allyourcodebase/zstd.git#1.5.7",
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

EDIT: this is ziglang/zig#21316