docs: embedded platform support design (#276)#277
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Design/proposal doc for entering the embedded Linux ecosystem, restructured as decisions-first (with rationale) then supporting detail. Positioning: mcpp brings its own matched-libc cross compiler (latest GCC) and consumes an external device sysroot — it is NOT a distro builder and never adapts per-vendor SDK. The single core change is opening the sysroot seam (L2); the CLibMode::Sysroot mechanism and the hermetic allow-list already accept tc.sysroot, so it's a minimal insertion. pkg-config and qemu cross test-run are xlings provisioning + thin wiring. Locks the maintainer decision register (16 decisions + rationale), incl.: - C++ source-only; binary interop C-ABI only + wrapper; vendor C++-only libs via a user-built C-bridge .so (built in vendor ABI, pure-C boundary) - glibc baseline pinned low when building payloads (GCC version x glibc decoupled); payloads use the latest GCC (16), GCC 15 is only the import-std capability floor - dropped: L4 backend mode, sysroot pinning/mgmt, .pc synthesis, and the "compiler doesn't support C++23" diagnostic (config II makes that case architecturally impossible) Beachhead: Raspberry Pi aarch64. Net work: P0 sysroot seam + matched-libc low-glibc GCC 16 payloads (+ one glibc-floor validation); P1 pkg-config + qemu test-run. Supersedes the earlier issue-276 analysis note (renamed to a proper design doc).
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嵌入式平台支持方案文档(回应 #276 的本地设计调研,非 issue 评论),从「issue 分析」重构为正式方案文档,结构改为决策点+理由前置,详情后置。
核心结论
CLibMode::Sysroot已能发--sysroot、hermetic 白名单已含tc.sysroot→ 最小改动。锁定的决策(16 条,含理由)
含:C++ 只源码 / 二进制只 C-ABI+封装;厂商 C++-only 库走用户建的 C 桥
.so;glibc 基线造 payload 时 pin 低(GCC 版本×glibc 解耦,payload 用最新 GCC 16,GCC 15 只是能力 floor);去掉 L4 后端、sysroot pinning、造.pc、以及「编译器不支持 C++23」诊断(架构上该场景不存在)。净工作
详见文档正文(决策表 + 现状核实/可行性/风险 + 关键文件索引 + Rust 对照)。