fix: retain emulated TLS during image LTO code generation

.github/workflows/ci.yml

@@ -155,6 +155,23 @@ jobs:
           OKRUN_PLACE=0 "$okrun" "$image" one two | tee anywhere.log
           grep -q "image ok: 3 args" anywhere.log || { echo "::error::the image placed anywhere"; exit 1; }
 
+      - name: ThinLTO keeps thread-local storage emulated
+        working-directory: checks/lto
+        run: |
+          t='${{ matrix.arch }}-openkal'
+          other=x86_64; [ '${{ matrix.arch }}' = x86_64 ] && other=aarch64
+          mcpp run --release --target "$t" | tee lto.log
+          grep -q 'LTO TLS ok' lto.log || { echo "::error::LTO TLS isolation failed"; exit 1; }
+          mcpp build --release --target "$other-openkal"
+          py=python3; command -v python3 > /dev/null 2>&1 && python3 -c '' 2>/dev/null || py=python
+          "$py" - <<'PY'
+          from pathlib import Path
+          for arch in ('x86_64', 'aarch64'):
+              objects = list(Path('target', arch + '-openkal').rglob('main.o'))
+              if not any(p.read_bytes()[:4] == b'BC\xc0\xde' for p in objects):
+                  raise SystemExit('no ThinLTO bitcode object for ' + arch)
+          PY
+
       - name: A snapshot of a C++ program's initialisers (0.23.0)
         working-directory: checks/snapshot
         run: |

README.md

@@ -41,6 +41,11 @@ mcpp pack --target x86_64-openkal --pkg-format okb        # one file okrun runs
 | hosted | the toolchain and the layers for the host triples, over the system's openkal implementation |
 | versions | the release group of the openkal family |
 
+Platform 0.23.6 also sets emulated TLS for the linker's LTO code generation.
+Compiling bitcode with `-femulated-tls` alone does not retain that choice at the
+final link. Both ordinary object files and ThinLTO builds use the platform's
+emulated thread-local storage.
+
 A project overrides any group under `[target.<selector>]`, for example
 `[target.'cfg(platform = "openkal")'.layers] "c++-abi" = false`, and selects
 another platform, or none, with `platform = "..."` or `--platform`.

checks/lto/mcpp.toml

@@ -0,0 +1,16 @@
+[package]
+name = "image-lto"
+version = "0.1.0"
+
+[language]
+standard = "c++23"
+
+[build]
+cxxflags = ["-flto=thin"]
+
+[target.'cfg(os = "openkal")']
+platform = { path = "../.." }
+
+[targets.image-lto]
+kind = "bin"
+main = "src/main.cpp"

checks/lto/src/main.cpp

@@ -0,0 +1,17 @@
+#include <cstdio>
+#include <thread>
+
+// Volatile accesses keep the TLS operations present under LTO, including the
+// main thread's read after a worker changes its own instance.
+thread_local volatile int tls_value = 7;
+
+int main() {
+    int worker_value = 0;
+    std::thread worker([&] {
+        tls_value = 9;
+        worker_value = tls_value;
+    });
+    worker.join();
+    if (worker_value != 9 || tls_value != 7) return 1;
+    std::puts("LTO TLS ok");
+}

mcpp.toml

@@ -12,7 +12,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-platform"
-version     = "0.23.5"
+version     = "0.23.6"
 description = "The platform of ok images (<arch>-openkal): their toolchain, C library and C++ run-time, tools, compile and link conventions, seal, runner and carrier, as one versioned statement mcpp reads."
 license     = "Apache-2.0"
 authors     = ["mcpplibs"]
@@ -137,7 +137,8 @@ asmflags = ["-ffixed-x18", "-mno-outline-atomics", "-mbranch-protection=pac-ret+
 driver = "lld"
 start  = "ok_main"
 flags  = ["-shared", "-z", "max-page-size=65536", "-z", "pack-relative-relocs", "-z", "now", "-z", "noexecstack",
-          "--hash-style=both", "--gc-sections", "--icf=safe", "--eh-frame-hdr", "--build-id=sha1"]
+          "--hash-style=both", "--gc-sections", "--icf=safe", "--eh-frame-hdr", "--build-id=sha1",
+          "-mllvm", "-emulated-tls"]
 inputs = [{ from = ["okld", "note-source"], as = "ok-notes.S" }]
 exe    = "{name}.oke"
 shared = "lib{name}.okso"