Do not force linking of default link libs in Unix toolchain

fmeum · copybara-github · commit 2482322fedb4 · 2023-09-13T05:32:31.000-07:00
`libstdc++` (`libc++` on macOS) and `libm` are no longer linked in if none of their symbols are referenced, e.g., in a pure C target. Fixes #6221 Closes #19440. PiperOrigin-RevId: 565020923 Change-Id: I5e8e5d4b4e67d6eccddcfc6aab0c59005cc4553e
diff --git a/src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/cc_shared_library_integration_test.sh b/src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/cc_shared_library_integration_test.sh
@@ -76,10 +76,9 @@ function test_cc_test() {
 
 function test_number_of_linked_libs() {
   binary=$(find . -name binary)
-  expected_num_libs="6"
   num_libs=$(readelf -d  $binary | grep NEEDED | wc -l)
-  echo "$num_libs" | (grep -q  "$expected_num_libs" \
-    || (echo "Expected no more than "$expected_num_libs" linked libraries but was $num_libs" && exit 1))
+  echo "$num_libs" | (grep -q  "$EXPECTED_NUM_LIBS" \
+    || (echo "Expected $EXPECTED_NUM_LIBS linked libraries but was $num_libs" && exit 1))
 }
 
 test_shared_library_user_link_flags
diff --git a/src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/testenv.sh b/src/main/starlark/tests/builtins_bzl/cc/cc_shared_library/test_cc_shared_library/testenv.sh
@@ -15,3 +15,4 @@
 
 LDD_BINARY="ldd"
 RPATH="RUNPATH"
+EXPECTED_NUM_LIBS="5"
diff --git a/src/test/shell/bazel/cc_integration_test.sh b/src/test/shell/bazel/cc_integration_test.sh
@@ -1928,4 +1928,28 @@ function test_find_optional_cpp_toolchain_not_present_with_toolchain_resolution(
   assert_contains "Toolchain not found" bazel-bin/pkg/my_rule
 }
 
+function test_no_cpp_stdlib_linked_to_c_library() {
+  mkdir pkg
+  cat > pkg/BUILD <<'EOF'
+cc_binary(
+  name = 'example',
+  srcs = ['example.c'],
+)
+EOF
+  cat > pkg/example.c <<'EOF'
+int main() {}
+EOF
+
+  bazel build //pkg:example &> "$TEST_log" || fail "Build failed"
+  if is_darwin; then
+    otool -L bazel-bin/pkg/example &> "$TEST_log" || fail "otool failed"
+    expect_log 'libc'
+    expect_not_log 'libc\+\+'
+  else
+    ldd bazel-bin/pkg/example &> "$TEST_log" || fail "ldd failed"
+    expect_log 'libc'
+    expect_not_log 'libstdc\+\+'
+  fi
+}
+
 run_suite "cc_integration_test"
diff --git a/third_party/BUILD b/third_party/BUILD
@@ -583,14 +583,14 @@ alias(
     actual = "@maven//:org_mockito_mockito_core",
 )
 
-alias(
+filegroup(
     name = "turbine_direct",
-    actual = "@maven//:com_google_turbine_turbine",
+    srcs = ["turbine/turbine_direct.jar"],
 )
 
-alias(
+java_import(
     name = "turbine",
-    actual = "@maven//:com_google_turbine_turbine",
+    jars = ["turbine/turbine_direct.jar"],
 )
 
 java_library(
diff --git a/tools/cpp/unix_cc_configure.bzl b/tools/cpp/unix_cc_configure.bzl
@@ -421,7 +421,34 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
     ), ":")
 
     use_libcpp = darwin or bsd
-    bazel_linklibs = "-lc++:-lm" if use_libcpp else "-lstdc++:-lm"
+    is_as_needed_supported = _is_linker_option_supported(
+        repository_ctx,
+        cc,
+        "-Wl,-no-as-needed",
+        "-no-as-needed",
+    )
+    is_push_state_supported = _is_linker_option_supported(
+        repository_ctx,
+        cc,
+        "-Wl,--push-state",
+        "--push-state",
+    )
+    if use_libcpp:
+        bazel_default_libs = ["-lc++", "-lm"]
+    else:
+        bazel_default_libs = ["-lstdc++", "-lm"]
+    if is_as_needed_supported and is_push_state_supported:
+        # Do not link against C++ standard libraries unless they are actually
+        # used.
+        # We assume that --push-state support implies --pop-state support.
+        bazel_linklibs_elements = [
+            arg
+            for lib in bazel_default_libs
+            for arg in ["-Wl,--push-state,-as-needed", lib, "-Wl,--pop-state"]
+        ]
+    else:
+        bazel_linklibs_elements = bazel_default_libs
+    bazel_linklibs = ":".join(bazel_linklibs_elements)
     bazel_linkopts = ""
 
     link_opts = split_escaped(get_env_var(
@@ -585,11 +612,8 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
             "%{conly_flags}": get_starlark_list(conly_opts),
             "%{link_flags}": get_starlark_list((
                 ["-fuse-ld=" + gold_or_lld_linker_path] if gold_or_lld_linker_path else []
-            ) + _add_linker_option_if_supported(
-                repository_ctx,
-                cc,
-                "-Wl,-no-as-needed",
-                "-no-as-needed",
+            ) + (
+                ["-Wl,-no-as-needed"] if is_as_needed_supported else []
             ) + _add_linker_option_if_supported(
                 repository_ctx,
                 cc,

Original file line number	Diff line number	Diff line change
`@@ -15,3 +15,4 @@`
`15`	`15`
`16`	`16`	`LDD_BINARY="ldd"`
`17`	`17`	`RPATH="RUNPATH"`
	`18`	`+EXPECTED_NUM_LIBS="5"`
Original file line number	Diff line number	Diff line change
`@@ -583,14 +583,14 @@ alias(`
`583`	`583`	`actual = "@maven//:org_mockito_mockito_core",`
`584`	`584`	`)`
`585`	`585`
`586`		`-alias(`
	`586`	`+filegroup(`
`587`	`587`	`name = "turbine_direct",`
`588`		`- actual = "@maven//:com_google_turbine_turbine",`
	`588`	`+ srcs = ["turbine/turbine_direct.jar"],`
`589`	`589`	`)`
`590`	`590`
`591`		`-alias(`
	`591`	`+java_import(`
`592`	`592`	`name = "turbine",`
`593`		`- actual = "@maven//:com_google_turbine_turbine",`
	`593`	`+ jars = ["turbine/turbine_direct.jar"],`
`594`	`594`	`)`
`595`	`595`
`596`	`596`	`java_library(`