Build Target Task 2: Multi-Platform LLVM Support and Bootable Code Generation

[cpunion]

Summary

Implements ESP Clang multi-platform support for cross-compilation to embedded platforms. This is part of Task 2 (#1201) from the cross-platform compilation design.

Task 2 Implementation TODO

Multi-Platform LLVM Support

• ESP Clang integration foundation
• Prebuilt compiler distribution system
  • On-demand compiler downloading for development
    • LLGO_CACHE_DIR/crosscompile/esp-clang-${version}
  • Embed clang distribution support
    • LLGO_ROOT/crosscompile/clang
  • Support all target platforms (X86, ARM, AArch64, AVR, MIPS, RISC-V, WebAssembly, Xtensa)
    • https://github.com/goplus/espressif-llvm-project-prebuilt

Target Configuration Support

• Integration with Task 1 target system
  • Always uses esp-clang
  • GOOS/GOARCH uses clang++ to compatible with c++
  • -target=xxx uses clang so doesn't compatible with c++ (without libc++ for embed platform)
• Code generation config (code-model, target-abi, relocation-model)
  - [ ] Stack configuration (default-stack-size, automatic-stack-size)

Bootable Code Generation

• Linker script integration
• Extra files support (startup code)
• Binary format output (esp32, esp32c3, esp8266)
  • uf2, nrf-dfu
• llgo build -target supports binary-format

Related

Compiler integration

• How to embed clang?
• Release
• Homebrew
• Linux pkgs

Runtime Integration

• compiler-rt
• libc
• CMSIS, nrfx mdk
• Embeded GC

Flash Programming

• Flash methods (openocd, msd, command)
• Flash command templates
• MSD programming support
• OpenOCD integration

Command Integration

• llgo run -target (emulator)
• llgo install -target (build + flash)
• llgo monitor?

Related Issues

• Proposal: Build Target Design #1176 (Cross-platform compilation design)
• Build Target Task 1: Basic Target Parameter Support for llgo build/run/test commands #1194 (Task 1 - Basic Target Parameter Support)
• Build Target Task 2: Multi-Platform LLVM Support and Bootable Code Generation #1201 (Task 2 - Multi-Platform LLVM Support)

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 72.34848% with 146 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.79%. Comparing base (6de3bdc) to head (ddc61ad).
⚠️ Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/crosscompile/crosscompile.go	63.77%	75 Missing and 17 partials ⚠️
internal/crosscompile/fetch.go	60.00%	25 Missing and 15 partials ⚠️
internal/clang/clang.go	94.78%	4 Missing and 2 partials ⚠️
internal/targets/config.go	0.00%	5 Missing ⚠️
internal/targets/loader.go	94.44%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1203      +/-   ##
==========================================
- Coverage   88.15%   87.79%   -0.37%     
==========================================
  Files          34       35       +1     
  Lines        8470     8928     +458     
==========================================
+ Hits         7467     7838     +371     
- Misses        934      979      +45     
- Partials       69      111      +42     

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