examples: 一份源码,两台机器,中间什么都没改

原来这个目录叫 baremetal 并且 [build] target 钉死在 riscv64-none-elf —— 那让它
成了一个「裸机的例子」,而不是设计文档那条主张的**演示**。

主张是:openkal 之上的程序,构建时不关心底下是哪个实现。所以现在:

  mcpp run                             这台机器,openkal-linux 之上
  mcpp run --target riscv64-none-elf   riscv64,OpenSBI 之上,没有操作系统

同一个 src/main.cpp,没有 #if,没有第二个目录,两边打印同样的四行。

唯一不同的是内存布局,而 build.mcpp 把它放在一个对 target_os 的条件后面 ——
因为那是一句关于**机器**的陈述,不是关于程序的。

CI 两步:第二步跑宿主那条,并且  两边的四行 —— 断言的是「输出相同」而不是
「两边都有输出」。

已验证两个方向都通过。目录改名为 same-source,因为它现在说的是这件事。

Author: speak-agent

.github/workflows/ci.yml

@@ -155,11 +155,11 @@ jobs:
           echo "$(cd "$(dirname "$BUILT")" && pwd)" >> "$GITHUB_PATH"
           "$BUILT" --version
 
-      - name: The same program on bare metal, with exceptions
+      - name: The same source on bare metal, with exceptions
         if: matrix.toolchain == 'llvm@22.1.8'
         run: |
           set -euo pipefail
-          cd examples/baremetal
+          cd examples/same-source
           Q=$(ls -d "$HOME"/.mcpp/registry/data/xpkgs/xim-x-qemu-riscv/*/bin/qemu-system-riscv64 | head -1)
           # ⚠️ Anchored on the BARE NAME, so a checkout that already carries a
           # path is left alone rather than getting a path inside a path. The
@@ -172,4 +172,21 @@ jobs:
           grep -q 'sorted: 2 4 7'   out.log   # containers + algorithms + the allocator
           grep -q 'caught: 42'      out.log   # the unwinder found the handler
           grep -q 'unwound: true'   out.log   # ⭐ and ran a destructor on the way
-          grep -q 'baremetal import std: ok' out.log
+          grep -q 'import std over openkal: ok' out.log
+
+      # ⭐⭐ AND THE SAME SOURCE ON THIS MACHINE, WHICH IS WHAT MAKES THE STEP
+      # ABOVE A DEMONSTRATION RATHER THAN AN ILLUSTRATION.
+      #
+      # Nothing is edited between the two commands — no `#if`, no second
+      # directory, no second source. The only thing that differs is the memory
+      # layout, and `build.mcpp` states it behind a condition on the target OS
+      # because that is a statement about the machine.
+      - name: The same source, on this machine, over openkal-linux
+        if: matrix.toolchain == 'llvm@22.1.8'
+        run: |
+          set -euo pipefail
+          cd examples/same-source && mcpp run 2>&1 | tee host.log
+          grep -q 'import std over openkal: ok' host.log
+          # The four lines are the same four lines.
+          diff <(grep -E '^(sorted|caught|unwound|import std over openkal):' out.log) \
+               <(grep -E '^(sorted|caught|unwound|import std over openkal):' host.log)

examples/baremetal/build.mcpp

@@ -0,0 +1,26 @@
+import mcpp;
+#include <cstring>
+
+int main() {
+    // ⭐⭐ THE LINKER SCRIPT IS FOR THE MACHINE WITH NO OPERATING SYSTEM, AND
+    // ONLY FOR IT. THAT CONDITION IS WHAT MAKES THIS ONE PROJECT INSTEAD OF TWO.
+    //
+    // The claim the design document makes is that a program above openkal is
+    // built without regard to which implementation is beneath — same source,
+    // different machine, nothing edited. A directory that could only be built
+    // one way would illustrate that claim rather than demonstrate it.
+    //
+    // So: `mcpp run` puts this on the host over openkal-linux, and
+    // `mcpp run --target riscv64-none-elf` puts the SAME source on riscv64 over
+    // OpenSBI. Both print the same four lines. The only thing that differs is
+    // the memory layout, which is a statement about the machine — and it is
+    // stated here, once, behind the condition that says which machine.
+    if (std::strcmp(mcpp::target_os(), "none") == 0) {
+        // A relative path in `ldflags` would resolve against the build
+        // directory; `link-script` resolves against the package root.
+        mcpp::link_script("link.ld");
+    }
+    mcpp::rerun_if_changed("link.ld");
+    mcpp::rerun_if_env_changed("MCPP_TARGET_OS");
+    return 0;
+}

examples/same-source/build.mcpp

@@ -1,9 +1,17 @@
 [package]
-name    = "openkal-baremetal-import-std"
+name    = "openkal-same-source"
 version = "0.1.0"
 
-[build]
-target = "riscv64-none-elf"
+# ⚠️ NO `[build] target`, AND THAT IS THE POINT OF THE DIRECTORY.
+#
+# The same `src/main.cpp` is built two ways from here:
+#
+#     mcpp run                              — this machine, over openkal-linux
+#     mcpp run --target riscv64-none-elf    — riscv64, over OpenSBI, no OS
+#
+# and both print the same four lines. Pinning a target here would make the
+# second command the only one, and then the directory would be an example of
+# bare metal rather than a demonstration that the source does not know.
 
 # No sysroot: there is no system to take headers or libraries from. The runner
 # is the emulator with firmware, because `-bios default` is what supplies the

examples/baremetal/link.ld examples/same-source/link.ldexamples/baremetal/link.ld renamed to examples/same-source/link.ld

@@ -1,7 +1,16 @@
 // `import std;` on a machine with no operating system.
 //
-// ⭐ THIS IS THE ACCEPTANCE CRITERION, AND ITS VALUE IS THAT IT CANNOT GO GREEN
-// BY ACCIDENT.
+// ⭐⭐ ONE SOURCE, TWO MACHINES, NOTHING EDITED BETWEEN THEM.
+//
+//     mcpp run                             — this machine, over openkal-linux
+//     mcpp run --target riscv64-none-elf   — riscv64, over OpenSBI, no OS
+//
+// Both print the same four lines. That is the claim the design document makes
+// about building above openkal, written as something a reader can run rather
+// than something they have to believe.
+//
+// ⭐ AND THE SECOND COMMAND IS THE ACCEPTANCE CRITERION, BECAUSE IT CANNOT GO
+// GREEN BY ACCIDENT.
 //
 // A hosted target has a C library, a C++ runtime and an unwinder already
 // installed, and a program that reaches one of them by mistake still works ---
@@ -55,6 +64,6 @@ int main() {
     // is consumed by a consteval constructor, and a value computed at run time
     // cannot be one. The compiler says so, which is the whole reason it is
     // written this way.
-    std::println("baremetal import std: {}", ok ? "ok" : "FAILED");
+    std::println("import std over openkal: {}", ok ? "ok" : "FAILED");
     return ok ? 0 : 1;
 }

examples/baremetal/mcpp.toml examples/same-source/mcpp.tomlexamples/baremetal/mcpp.toml renamed to examples/same-source/mcpp.toml

@@ -158,7 +158,7 @@ include_dirs = ["llvm-generated/freestanding"]
 #
 #   The symbols are `__eh_frame_start` / `__eh_frame_end` (and the `_hdr_`
 #   pair), and AddressSpace.hpp carries the linker script fragment that defines
-#   them. examples/baremetal/link.ld is that fragment.
+#   them. examples/same-source/link.ld is that fragment.
 cxxflags = ["-D_LIBUNWIND_USE_DLADDR=0", "-D_GNU_SOURCE",
             "-D_LIBUNWIND_IS_BAREMETAL=1"]
 # ⚠️ THE FLAG BELONGS TO THIS PACKAGE AND LANDS ON THE CONSUMER'S LINK.