docs(plan): §4.2 回填 —— 测量证实了源码包这一列 - #554
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⚠️ ⚠️ 我先做了 prebuilt(`xim:picolibc-arm`),把 §4.2 右列的每一项代价都付了一遍, 走完之后才回到源码包。记下来,是因为结论会被复查而理由不会 —— 而这次理由拿到了证据: * 七份 include 树逐字节相同(含 meson 生成的 picolibc.h/newlib.h)⇒ prebuilt 发了 同一个目录的七份拷贝; * 七个档位的源文件列表完全相同 ⇒ 档位之间只差编译标志; * 按 <march>/<mabi> 索引时七档塌成五个目录,软浮点行拿到带 Tag_ABI_HardFP_use 的 库 ⇒ prebuilt 的多库键在 ARM 上不可能正确,而构建期毫无迹象。 源码包自己的代价也测出来了(四条「上游按归档分层而扁平库不能」),外加一条只有跑 才能发现的:板级启动必须设线程指针,否则程序链接干净、运行、什么都不打印、挂住。
… decisions Records what the ecosystem batch measured: upstream-derived packages take upstream's namespace and version (verified byte for byte against both upstream releases); a bare requirement in mcpp is an exact pin and not a caret, which shipped two broken releases before the diagnostic was understood; an escaping path dependency is invisible to the publishing repository's own CI; a `main` that returns hung for ever because every test took the one path that worked; and one open question — `mcpp run` folds every non-zero exit status to 1.
Observed three times in the sandbox verification, always on the `mcpp run` after a `mcpp build`: ninja at 99.9% CPU with zero children and zero system time, on a complete eight-edge graph with nothing to do. Not the graph — the host runs the same project, with the same two `stage_file` edges, in about two seconds. Not reproducible on demand afterwards in the same sandbox. One difference recorded without a claim: the sandbox's ninja and the host's are different binaries at the same version. The deterministic corollary is worth fixing regardless: killing `mcpp run` does not kill its ninja, so every timed-out step leaks a spinning core — one orphan outlived the removal of its entire sandbox.
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docs(plan): §4.2 回填 —— 我先走了被否掉的那条,而测量证实了这张表
xim:picolibc-arm),把 §4.2 右列的每一项代价都付了一遍,走完之后才回到源码包。记下来,是因为结论会被复查而理由不会 —— 而这次理由拿到了证据:
同一个目录的七份拷贝;
库 ⇒ prebuilt 的多库键在 ARM 上不可能正确,而构建期毫无迹象。
源码包自己的代价也测出来了(四条「上游按归档分层而扁平库不能」),外加一条只有跑
才能发现的:板级启动必须设线程指针,否则程序链接干净、运行、什么都不打印、挂住。