2026.9.21.3 — a token that did nothing, a count that was wrong, and a build that measured the dependencies

.agents/docs/2026-09-21-macros-and-withdrawal-verify.sh

@@ -297,6 +297,99 @@ else
     skip "openkal-llvm-runtime 0.14.0 did not resolve from the index"
 fi
 
+# ── CHANGE. `builtins = "iso"` withdraws the Apple pattern fill ─────────────
+section "G. builtins = \"iso\" emits -fno-builtin (CHANGE)"
+# A CODE-GENERATION PROPERTY, so the reading is an object file rather than a
+# `-dM` dump — which is exactly why the token this asserts was a silent no-op
+# for the whole of its first life. `2026.9.21.2` and earlier emit
+# `-fno-builtin-memset_pattern16`; clang matches `-fno-builtin-<fn>` against
+# its builtin table, `memset_pattern16` is an LLVM TargetLibraryInfo libfunc
+# and not in it, so the flag is accepted in silence and the call survives. On
+# those versions the aarch64-macos link fails with
+#
+#     ld64.lld: error: undefined symbol: memset_pattern16
+#
+# so a failed build here IS the negative reading rather than an absent one.
+g="$root/g"; rm -rf "$g"; mkdir -p "$g/src"
+cat > "$g/src/main.cpp" <<'EOF'
+extern "C" void fill(int* a, long n) {
+    for (long i = 0; i < n; ++i) a[i] = 0x01020304;
+}
+int main() { static int buf[64]; fill(buf, 64); return buf[0] == 0x01020304 ? 0 : 1; }
+EOF
+# `-O2` per package rather than --release: the idiom pass does not run at the
+# dev profile's -O0, and a release build would compile the runtime a second
+# time in a second profile for no reading.
+cat > "$g/mcpp.toml" <<'EOF'
+[package]
+name    = "builtins-probe"
+version = "0.1.0"
+
+[build]
+cxxflags = ["-O2"]
+
+[dependencies]
+openkal-llvm-runtime = "0.15.0"
+
+[toolchain]
+default = "llvm@22.1.8"
+EOF
+gnm=$(ls "$HOME"/.xlings/data/xpkgs/xim-x-llvm/22.1.8/bin/llvm-nm 2>/dev/null | head -1)
+if [ -z "$gnm" ]; then
+    skip "G: no llvm-nm in the payload to read the object with"
+elif (cd "$g" && "$STORE" build --target aarch64-macos >/dev/null 2>&1); then
+    gobj=$(find "$g/target" -name 'main.o' 2>/dev/null | head -1)
+    if [ -z "$gobj" ]; then
+        fail "G: the build reported success and produced no object"
+    elif [ "$("$gnm" -u "$gobj" 2>/dev/null | grep -c memset_pattern16)" = 0 ]; then
+        ok "builtins = \"iso\" leaves no memset_pattern16 in the object"
+    else
+        fail "builtins = \"iso\" did not withdraw memset_pattern16"
+    fi
+else
+    fail "G: the aarch64-macos build did not complete (the old token's signature)"
+fi
+
+# ── CHANGE. `mcpp test --no-run` ────────────────────────────────────────────
+section "H. mcpp test --no-run builds the tests and says so (CHANGE)"
+# Before this release the flag does not exist and the command exits non-zero
+# with "unknown option: --no-run". The runner named here is a program that
+# does not exist, which produces "tests built, nothing run" on every host for
+# the native target with nothing installed.
+h="$root/h"; rm -rf "$h"; mkdir -p "$h/tests"
+printf 'int main() { return 0; }\n' > "$h/tests/alpha.cpp"
+printf 'int main() { return 0; }\n' > "$h/tests/beta.cpp"
+printf '[package]\nname = "norun"\nversion = "0.1.0"\n' > "$h/mcpp.toml"
+hhost=$("$STORE" --print-target 2>/dev/null || true)
+if [ -z "$hhost" ]; then
+    (cd "$h" && "$STORE" build >/dev/null 2>&1) || true
+    hhost=$(ls "$h/target" 2>/dev/null | grep -v '^\.' | head -1)
+fi
+if [ -z "$hhost" ]; then
+    skip "H: could not determine the host triple"
+else
+    cat > "$h/mcpp.toml" <<EOF
+[package]
+name    = "norun"
+version = "0.1.0"
+
+[target.$hhost]
+runner = ["mcpp-no-such-runner-exists"]
+EOF
+    hout=$( (cd "$h" && "$STORE" test --target "$hhost" --no-run 2>&1) )
+    hrc=$?
+    case "$hout" in
+        *"2 built, not run"*)
+            if [ "$hrc" = 0 ]; then
+                ok "--no-run builds the tests and exits 0"
+            else
+                fail "--no-run reported the built tests and exited $hrc"
+            fi ;;
+        *) fail "--no-run did not report two tests as built" ;;
+    esac
+fi
+
+
 printf '\n-- summary --\nfails=%d\nnot run:%s\n' "$fails" "${skipped:-
   (none)}"
 [ "$fails" -eq 0 ]

.github/workflows/openkal-cross.yml

@@ -264,6 +264,129 @@ jobs:
             echo "${{ matrix.host }} → $t : $(ls -l "$a" | awk '{print $5}') bytes"
           done
 
+      # THE ONLY CRITERION THE `builtins` TOKEN HAS, AND WHY IT IS HERE.
+      #
+      # `[c-abi] builtins = "iso"` states that the C library supplies the ISO
+      # functions and no vendor extensions. On Darwin targets clang's loop
+      # idiom recogniser rewrites a constant-pattern fill into a call to
+      # `memset_pattern16`, an Apple libc extension no such library carries.
+      # That call is produced by the code generator, so it appears in no `-D`
+      # and in no preprocessor dump --- and `mcpp.toolchain.cenv` verifies its
+      # tokens by comparing a `-dM` dump. The token this mechanism emitted was
+      # therefore a silent no-op for the whole of its first life, and this
+      # step exists because no other kind of check could have reported it.
+      #
+      # LEG 1 IS THE DENOMINATOR, AND IT IS NOT DECORATION. At `-O0` the pass
+      # does not run, and `-ffreestanding` implies `-fno-builtin`; an
+      # assertion that only reads "the symbol is absent" therefore passes in
+      # several worlds where nothing was measured. Leg 1 compiles with no flag
+      # at all and fails if the symbol does NOT appear.
+      #
+      # LEG 2 PINS THE DEFECT ITSELF. `-fno-builtin-memset_pattern16` is
+      # accepted in silence and changes nothing: `-fno-builtin-<fn>` is matched
+      # against clang's builtin table, and `memset_pattern16` is an LLVM
+      # TargetLibraryInfo libfunc rather than a clang builtin. The toolchain is
+      # pinned in this job, so the reading is stable. Should a later pin make
+      # leg 2 fail, clang has gained the narrower behaviour, and `cenv` can
+      # emit the narrower flag and recover the 1.8 per cent `-fno-builtin`
+      # costs.
+      #
+      # LEG 3 IS THE ENGINE: the same idiom, over the openkal stack, for
+      # `aarch64-macos`, built by the mcpp under test. Measured on the token
+      # this step was written for, the two readings are
+      #
+      #     -fno-builtin-memset_pattern16   1 reference, and the link fails
+      #     -fno-builtin                    0 references, and it links
+      #
+      # so a regression here reports itself at the link before the assertion
+      # is reached. The assertion covers the remaining case, in which some
+      # layer happens to supply the symbol and the link succeeds anyway.
+      #
+      # `-O2` IS PER PACKAGE RATHER THAN `--release`. The idiom pass does not
+      # run at the dev profile's `-O0`, and a release build would compile the
+      # runtime a second time in a second profile for no reading.
+      - name: builtins = "iso" withdraws the Apple pattern fill
+        run: |
+          set -euo pipefail
+          BIN="${MCPP_HOME:-$HOME/.mcpp}/registry/data/xpkgs/xim-x-llvm/22.1.8/bin"
+          # Not `ls ... | head -1`: with `pipefail` the absent candidate's
+          # exit status ends the step before the guard below is reached.
+          pick() {  # $1..$n = candidate paths; prints the first executable one
+            for c in "$@"; do
+              if [ -x "$c" ]; then printf '%s' "$c"; return 0; fi
+            done
+            return 1
+          }
+          CLANG="$(pick "$BIN/clang" "$BIN/clang.exe")" \
+            || { echo "::error::no clang under $BIN"; exit 1; }
+          NM="$(pick "$BIN/llvm-nm" "$BIN/llvm-nm.exe")" \
+            || { echo "::error::no llvm-nm under $BIN"; exit 1; }
+
+          # Inside the clone, so the dependency is named by a relative path.
+          # `$RUNNER_TEMP` is a backslash path on the Windows host and a TOML
+          # string would read its separators as escapes.
+          W="$RUNNER_TEMP/okl/examples/builtins-probe"
+          rm -rf "$W"; mkdir -p "$W/src"
+
+          # The one shape the idiom recogniser rewrites. The element type is
+          # `int` and not `char` because a byte-repeating value becomes
+          # `memset`, which every C library has.
+          cat > "$W/src/main.cpp" <<'PROBE'
+          extern "C" void fill(int* a, long n) {
+              for (long i = 0; i < n; ++i) a[i] = 0x01020304;
+          }
+
+          int main() {
+              static int buf[64];
+              fill(buf, 64);
+              return buf[0] == 0x01020304 ? 0 : 1;
+          }
+          PROBE
+
+          cat > "$W/mcpp.toml" <<'PROJECT'
+          [package]
+          name    = "openkal-builtins-probe"
+          version = "0.1.0"
+
+          [build]
+          cxxflags = ["-O2"]
+
+          [dependencies]
+          openkal-llvm-runtime = { path = "../.." }
+
+          [toolchain]
+          default = "llvm@22.1.8"
+          PROJECT
+
+          # THE READER ASKS FOR UNDEFINED SYMBOLS, NOT FOR BYTES.
+          #
+          # This was `grep -ac memset_pattern16`, on the reasoning that the name
+          # is in the object's string table and a byte match needs no tool. It
+          # reads 1/0 correctly with GNU grep and read 0 for all three legs on
+          # the macOS host, where grep is BSD: the object is binary, and what
+          # `-a` promises about that differs between the two. Leg 1 is what
+          # reported it. `llvm-nm` is in the payload beside the clang already
+          # being used, and answers the question this step is actually asking.
+          refs() { "$NM" -u "$1" 2>/dev/null | grep -c memset_pattern16 || true; }
+          T=--target=arm64-apple-macos14.0
+
+          "$CLANG" $T -O2                                -c "$W/src/main.cpp" -o "$W/bare.o"
+          "$CLANG" $T -O2 -fno-builtin-memset_pattern16  -c "$W/src/main.cpp" -o "$W/narrow.o"
+          "$CLANG" $T -O2 -fno-builtin                   -c "$W/src/main.cpp" -o "$W/blunt.o"
+          echo "no flag                       : $(refs "$W/bare.o")"
+          echo "-fno-builtin-memset_pattern16 : $(refs "$W/narrow.o")"
+          echo "-fno-builtin                  : $(refs "$W/blunt.o")"
+
+          [ "$(refs "$W/bare.o")" = 1 ] || { echo "::error::leg 1: the probe no longer triggers the idiom, so legs 2 and 3 measure nothing"; exit 1; }
+          [ "$(refs "$W/narrow.o")" = 1 ] || { echo "::error::leg 2: clang now honours -fno-builtin-memset_pattern16, and mcpp.toolchain.cenv can emit the narrower token"; exit 1; }
+          [ "$(refs "$W/blunt.o")" = 0 ] || { echo "::error::leg 2: -fno-builtin no longer withdraws the pattern fill"; exit 1; }
+
+          (cd "$W" && "$MCPP_UNDER_TEST" build --target aarch64-macos)
+          obj=$(find "$W/target" -name 'main.o' | head -1)
+          [ -n "$obj" ] || { echo "::error::leg 3 produced no object to read"; exit 1; }
+          echo "engine, aarch64-macos over openkal: $(refs "$obj")"
+          [ "$(refs "$obj")" = 0 ] || { echo "::error::leg 3: builtins = \"iso\" did not withdraw memset_pattern16"; exit 1; }
+
       - uses: actions/upload-artifact@v4
         with:
           name: openkal-built-on-${{ matrix.host }}

CHANGELOG.md

@@ -3,7 +3,113 @@
 > 本文件追踪 `mcpp-community/mcpp` 公开仓的版本演进。
 > 格式参考 [Keep a Changelog](https://keepachangelog.com/zh-CN/1.1.0/)。
 
-## [Unreleased]
+## [2026.9.21.3] - 2026-09-21
+
+### `mcpp test --no-run`:为一个跑不了的目标构建测试,并把这当成答案
+
+一个本机既不能执行、也没有 runner 可达的目标,会让每个测试停在 `not run`,命令退出 2。
+这是对「这些测试通过吗」的正确回答——mcpp 没有查明。但 **2 同样是 runner 坏掉时的
+退出码**,于是一个只想要「构建」的调用方无法区分这两者,只能退回去用 `mcpp build`。
+
+而 `mcpp build` 构建的是**包**。对一个源码只在 `tests/` 下的包,它一行都不编译。
+实测 mcpp-index 的 `archive` 成员(源码是 `tests/` 下两个文件):
+
+```
+$ mcpp build --target aarch64-macos      # 退出 0
+   Compiling compat.lz4 / compat.xz / compat.zlib / compat.zstd ...
+$ find target -name '*compression*' -o -name '*versions*'
+   (只有 musl 的 versionsort.o)
+```
+
+退出 0,编译了这个成员的**依赖**,而**该成员自己的代码一行都没有编过**。一个读这个
+退出码的兼容性测量,会把它记成「这个成员在 macOS 上构建通过」。
+
+`--no-run` 让那个更窄的断言有了自己的答案:被选中的每个测试都为该目标编译并链接,
+没有任何一个被执行,结果也这么写:
+
+```
+test result ok. 0 passed; 0 failed; 2 built, not run
+```
+
+`built` 与 `not_run` 分开计数,机器接口也一样(`docs/50`):`not_run` 是「试过而做不到,
+问题悬着,退出 2」,`built` 是「被要求不要执行,构建就是问题的全部,退出 0」。编译不过
+的测试仍然是失败。`--no-run` 与 `--no-runner` 同时给出会被拒绝——两个名字只差一个字符
+而含义相反,不存在应当优先的那一个读法。
+
+判据是 `tests/e2e/745_no_run_builds_the_tests_and_says_so.sh`,四条腿。其中 runner 用的是
+一个**不存在的程序名**:用一个执行不了的目标会让这个测试需要交叉工具链和特定宿主,而
+一个找不到的 runner 在每台宿主上、对本机目标、不装任何东西,就能造出同一个局面。
+
+### `builtins = "iso"` 发的那个 token 是静默空操作,已换成 `-fno-builtin`
+
+`[c-abi] builtins = "iso"` 声明 C 库只提供 ISO 函数、没有厂商扩展。Apple 目标上
+clang 的循环惯用法识别会把常量模式填充改写成 `memset_pattern16` 调用——那是一个
+Apple libc 扩展,这样的库没有它。此前这里发的是 `-fno-builtin-memset_pattern16`。
+在一份真实的 `build.ninja` 编译命令上做 A/B,只改这一个 flag:
+
+| flag | `memset_pattern16` 引用数 |
+|---|---|
+| 照原样(flag 在) | 1 |
+| flag **删掉** | 1 |
+| `-fno-builtin` | 0 |
+| `-mllvm -disable-loop-idiom-memset` | 0 |
+
+**而它报不出自己什么都没做。** clang 静默接受 `-fno-builtin-totally_not_a_function`:
+`-fno-builtin-X` 这一族按 clang 的 builtin 表校验,而 `memset_pattern16` 是 LLVM
+TargetLibraryInfo 的 libfunc,不在那张表里;发出调用的是 LoopIdiomRecognize,它查
+TLI,按函数名的属性到不了它。
+
+不选 `-mllvm` 的理由是它传的是 LLVM 内部选项,不是受支持的接口,改名或删除之后这套
+机制会再次静默失效——那正是这次要修的缺陷本身。代价是量出来的:在暴露此事的那个翻译
+单元(libarchive 的 7zip reader,`-O2`,aarch64-macos)上,目标文件从 38200 涨到
+38888 字节,1.8%,因为 `-fno-builtin` 同时撤走了 C 库确实提供的那些 ISO 函数。这比
+`builtins = "iso"` 声明的范围宽,而它宽在安全的方向:代码生成器不合成的调用不会变成
+链接错误。
+
+**这个空操作能活下来,是因为它没有判据。** `cenv` 的探针用 `-dM` dump 校验自己发的
+token,而代码生成阶段的性质在预处理器 dump 里不可见。判据现在在
+`.github/workflows/openkal-cross.yml`,三条腿,跑在三台宿主上:
+
+| 腿 | 内容 | 判据 |
+|---|---|---|
+| 1 | 不带任何 flag 编译探针 | 符号**必须出现**——否则探针已经触发不了惯用法,腿 2、3 什么都没测 |
+| 2 | `-fno-builtin-memset_pattern16` | 符号**仍必须出现**(钉住这个缺陷;若哪天红了,说明 clang 认了窄拼法,`cenv` 可以改回去把这 1.8% 拿回来) |
+| 3 | mcpp 为 `aarch64-macos` 走 openkal 栈构建同一份源码 | 目标文件里**零引用** |
+
+腿 3 的对照:换回旧 token,同一个工程链接失败于
+`ld64.lld: error: undefined symbol: memset_pattern16`。
+
+### 更正:那个「四个成员」是二,而分组用错了依据
+
+2026.9.21.2 的条目、`cenv.cppm` 与 `predefines.cppm` 的注释、`docs/21` 与 `docs/22`
+都写着「借来的 `__CYGWIN__` 代价是四个成员:archive、sqlite3、mimalloc、c-ares」。
+**撤销之后的重测把这个数目否掉了。**
+
+| 成员 | 记的真因 | 实测真因 | 撤销后 |
+|---|---|---|---|
+| `archive`(经 xz) | `__CYGWIN__` | **对** | **清了** |
+| `sqlite3` | `__CYGWIN__` | **对** | **清了** |
+| `c-ares` | `__CYGWIN__` | **错**:`#ifdef HAVE_WINDOWS_H`,而那个宏由 mcpp-index 自己的配方在 windows 分支 `#define` | 仍红 |
+| `mimalloc` | `__CYGWIN__` | **错**:已经不走到任何头文件——`error in backend: Target OS doesn't support __builtin_thread_pointer() yet` | 仍红 |
+
+**四个是按「诊断」分的组,不是按「真因」。** 四个都停在 `windows.h`(mimalloc 当时如此),
+于是被记成同一类。**按诊断分组不是按真因分组**,这样数出来的数目会高估一次撤销能修掉多少。
+
+这条更正本身来自判据:重测把总失败从 10 降到 5、**新增失败为零**,而「`windows.h` 组 4→0」
+这半条没有达成——是 4→2。**一个达成了一半的判据,比一个没写的判据更有价值:它指出了
+分母是错的。**
+
+### `mimalloc` 暴露出替身三元组的一个代价,与宏无关
+
+```
+fatal error: error in backend: Target OS doesn't support __builtin_thread_pointer() yet.
+```
+
+`presents = "posix"` 在 Windows 上实现成 `--target=x86_64-pc-cygwin`。LLVM 没有为那个
+OS 实现 `__builtin_thread_pointer()`,而 mimalloc 用它取线程局部堆指针。**这是替身
+三元组的第一个被测量到的、超出宏名之外的代价**;先前关于这次替换的记录只讨论了预处理器
+看到什么。
+
 
 ## [2026.9.21.2] - 2026-09-21
 

docs/08-testing.md

@@ -105,6 +105,7 @@ mcpp performs with the test binary appended.
 ```bash
 mcpp test --target thumbv7em-none-eabihf     # built for the board, run through its runner
 mcpp test --no-runner                        # ignore the runner and execute directly
+mcpp test --target aarch64-macos --no-run    # build the tests for the target and stop
 ```
 
 Nothing about the test changes. The same `tests/**/*.cpp` compiles for the
@@ -114,6 +115,23 @@ or a QEMU exit code is what a bare-metal runner is chosen to produce.
 `--no-runner` exists for a host that can execute the binaries natively and
 should not pay for an emulator.
 
+`--no-run` makes the narrower claim, and it has to be asked for. Without it, a
+target this host can neither execute nor reach through a runner leaves every
+test not run and the command exits 2: mcpp did not establish whether the tests
+pass, and reporting that as success is the false reading this repository has
+recorded most often. But 2 is also what a broken runner returns, so a caller
+that wanted only the build could not tell the two apart. Under `--no-run` every
+selected test is compiled and linked for the target, none is executed, and the
+result says so:
+
+```
+test result ok. 0 passed; 0 failed; 2 built, not run
+```
+
+A test that does not compile is still a failure, and `--no-run` with
+`--no-runner` is refused rather than resolved: one says to run the binaries
+without the declared runner, the other says not to run them.
+
 A test program carries the files it reads beside it: the runner receives
 `MCPP_RUNTIME_FILES`, the list of its deployed files and the shared libraries it
 loads, and a runner that moves the program to a device copies them with it. A