build: make megatron_core wheel byte-reproducible

scripts/dependence/build.sh

@@ -46,6 +46,21 @@ megatron_build (){
 
     python -m pip install --upgrade pip
     python -m pip install build "setuptools>=80" pybind11 packaging
+
+    # --- reproducible build ---------------------------------------------------
+    # Pin the wheel's embedded timestamps (zip member mtimes, RECORD) to the
+    # source commit time so rebuilding the SAME commit yields a byte-identical
+    # wheel. Falls back to a fixed epoch when the source is not a git checkout
+    # (e.g. built from a tarball), keeping `set -e` from aborting the build.
+    export SOURCE_DATE_EPOCH="$(git -C "$megatron_dir" show -s --format=%ct HEAD 2>/dev/null || echo 315532800)"
+    # Deterministic C/C++ compile + link flags for the helpers_cpp extension:
+    #   -ffile-prefix-map strips the absolute build path baked into the object,
+    #   -frandom-seed makes symbol mangling / gensyms stable across builds,
+    #   -g0 drops debug info, --build-id=none removes the random ELF build-id.
+    export CFLAGS="${CFLAGS:-} -ffile-prefix-map=${megatron_dir}=. -frandom-seed=helpers_cpp -g0"
+    export CXXFLAGS="${CXXFLAGS:-} -ffile-prefix-map=${megatron_dir}=. -frandom-seed=helpers_cpp -g0"
+    export LDFLAGS="${LDFLAGS:-} -Wl,--build-id=none"
+    # --------------------------------------------------------------------------
     NO_VCS_VERSION=1 python -m build --wheel --no-isolation
 
     echo "install_megatron_develop_whl"

setup.py

@@ -9,7 +9,21 @@
             "megatron.core.datasets.helpers_cpp",
             sources=["megatron/core/datasets/helpers.cpp"],
             language="c++",
-            extra_compile_args=["-O3", "-Wall", "-std=c++17"],
+            # Deterministic build flags so the compiled .so is byte-identical
+            # across rebuilds even when invoked directly (not via build.sh):
+            #   -frandom-seed stabilizes symbol/gensym mangling,
+            #   -ffile-prefix-map strips build paths from the object,
+            #   -g0 drops debug info; link flags drop the random ELF build-id
+            #   (-Wl,--build-id=none) and strip symbols (-Wl,-s).
+            extra_compile_args=[
+                "-O3",
+                "-Wall",
+                "-std=c++17",
+                "-ffile-prefix-map=.=.",
+                "-frandom-seed=helpers_cpp",
+                "-g0",
+            ],
+            extra_link_args=["-Wl,--build-id=none", "-Wl,-s"],
             optional=True,
         )
     ]