Introduce flag --@bazel_tools//tools/cpp:link_extra_libs

Numerous tools override --custom_malloc to add debugging or monitoring runtimes
(see e.g. sanitizers). While this is fine for cases where the tool must also
override malloc to function, in other cases it's simply misuse of
--custom_malloc where no other mechanism exists to link an extra library.

This becomes especially problematic where a runtime library is supposed to be
added in certain configurations that should run in production or other
performance sensitive builds. In these cases, we should _not_ override malloc,
which may also be specified by a cc_binary target. Doing so would introduce
unwanted changes, potentially affecting performance negatively.

To fix abuse of --custom_malloc, add --@bazel_tools//tools/cpp:link_extra_libs,
which is similar, but otherwise does not override other runtime libraries.

Finally, extra libraries are collected in //tools/cpp:link_extra_lib, which can
be used to also introduce libraries based on global configuration rather than
via the command line option.

PiperOrigin-RevId: 509191255
Change-Id: I932afafed574b0cf5f37a8358f6e12c43f59ba1c

Author: Googler

src/main/java/com/google/devtools/build/lib/bazel/rules/android/android_ndk_build_file_template.txt

@@ -24,6 +24,11 @@ filegroup(
     srcs = ["ndk"],
 )
 
+cc_library(
+    name = "link_extra_lib",
+    srcs = [],
+)
+
 cc_library(
     name = "malloc",
     srcs = [],

src/main/starlark/builtins_bzl/common/cc/cc_binary_attrs.bzl

@@ -70,6 +70,11 @@ cc_binary_attrs_with_aspects = {
         default = configuration_field(fragment = "cpp", name = "custom_malloc"),
         aspects = [graph_structure_aspect],
     ),
+    "_link_extra_lib": attr.label(
+        default = Label("@" + semantics.get_repo() + "//tools/cpp:link_extra_lib"),
+        providers = [CcInfo],
+        aspects = [graph_structure_aspect],
+    ),
     "stamp": attr.int(
         values = [-1, 0, 1],
         default = -1,
@@ -112,3 +117,6 @@ cc_binary_attrs_without_aspects["malloc"] = attr.label(
 cc_binary_attrs_without_aspects["_default_malloc"] = attr.label(
     default = configuration_field(fragment = "cpp", name = "custom_malloc"),
 )
+cc_binary_attrs_without_aspects["_link_extra_lib"] = attr.label(
+    default = Label("@" + semantics.get_repo() + "//tools/cpp:link_extra_lib"),
+)

src/main/starlark/builtins_bzl/common/cc/semantics.bzl

@@ -132,9 +132,15 @@ def _get_coverage_env(ctx):
 def _get_cc_runtimes(ctx, is_library):
     if is_library:
         return []
+
+    runtimes = [ctx.attr._link_extra_lib]
+
     if ctx.fragments.cpp.custom_malloc != None:
-        return [ctx.attr._default_malloc]
-    return [ctx.attr.malloc]
+        runtimes.append(ctx.attr._default_malloc)
+    else:
+        runtimes.append(ctx.attr.malloc)
+
+    return runtimes
 
 def _should_use_legacy_cc_test(_):
     return True

src/test/java/com/google/devtools/build/lib/packages/util/Crosstool.java

@@ -583,6 +583,8 @@ public void write() throws IOException {
                 "    name = 'interface_library_builder',",
                 "    srcs = ['build_interface_so'],",
                 ")",
+                // We add an empty :link_extra_lib target in case we need it.
+                "cc_library(name = 'link_extra_lib')",
                 // We add an empty :malloc target in case we need it.
                 "cc_library(name = 'malloc')",
                 // Fake targets to get us through loading/analysis.

src/test/java/com/google/devtools/build/lib/query2/testutil/AbstractQueryTest.java

@@ -684,6 +684,8 @@ public void testDeps() throws Exception {
       }
       String expectedDependencies =
           helper.getToolsRepository()
+              + "//tools/cpp:link_extra_lib + "
+              + helper.getToolsRepository()
               + "//tools/cpp:malloc + //configurable:main + "
               + "//configurable:main.cc + //configurable:adep + //configurable:bdep + "
               + "//configurable:defaultdep + //conditions:a + //conditions:b "
@@ -1016,6 +1018,7 @@ public void testNoImplicitDeps() throws Exception {
 
     // Implicit dependencies:
     String hostDepsExpr = helper.getToolsRepository() + "//tools/cpp:malloc";
+    hostDepsExpr += " + " + helper.getToolsRepository() + "//tools/cpp:link_extra_lib";
     if (!analysisMock.isThisBazel()) {
       hostDepsExpr += " + //tools/cpp:malloc.cc";
     }

src/test/shell/bazel/cc_flags_supplier_test.sh

@@ -56,6 +56,11 @@ function write_crosstool() {
 package(default_visibility = ["//visibility:public"])
 
 load(":cc_toolchain_config.bzl", "cc_toolchain_config")
+
+cc_library(
+    name = "link_extra_lib",
+)
+
 cc_library(
     name = "malloc",
 )

src/test/shell/integration/cpp_test.sh

@@ -168,6 +168,10 @@ package(default_visibility = ["//visibility:public"])
 
 load(":toolchain.bzl", "toolchains")
 
+cc_library(
+    name = "link_extra_lib",
+)
+
 cc_library(
     name = "malloc",
 )

tools/cpp/BUILD.empty.tpl

@@ -16,6 +16,10 @@ load(":cc_toolchain_config.bzl", "cc_toolchain_config")
 
 package(default_visibility = ["//visibility:public"])
 
+cc_library(
+    name = "link_extra_lib",
+)
+
 cc_library(
     name = "malloc",
 )

tools/cpp/BUILD.static.bsd

@@ -19,6 +19,24 @@ load("@rules_cc//cc:defs.bzl", "cc_library", "cc_toolchain", "cc_toolchain_suite
 
 package(default_visibility = ["//visibility:public"])
 
+cc_library(name = "empty_lib")
+
+# Label flag for extra libraries to be linked into every binary.
+# TODO(bazel-team): Support passing flag multiple times to build a list.
+label_flag(
+    name = "link_extra_libs",
+    build_setting_default = ":empty_lib",
+)
+
+# The final extra library to be linked into every binary target. This collects
+# the above flag, but may also include more libraries depending on config.
+cc_library(
+    name = "link_extra_lib",
+    deps = [
+        ":link_extra_libs",
+    ],
+)
+
 cc_library(
     name = "malloc",
 )

tools/cpp/BUILD.tools

@@ -66,6 +66,28 @@ cc_host_toolchain_alias(name = "current_cc_host_toolchain")
 
 cc_libc_top_alias(name = "current_libc_top")
 
+cc_library(
+    name = "empty_lib",
+    tags = ["__DONT_DEPEND_ON_DEF_PARSER__"],
+)
+
+# Label flag for extra libraries to be linked into every binary.
+# TODO(bazel-team): Support passing flag multiple times to build a list.
+label_flag(
+    name = "link_extra_libs",
+    build_setting_default = ":empty_lib",
+)
+
+# The final extra library to be linked into every binary target. This collects
+# the above flag, but may also include more libraries depending on config.
+cc_library(
+    name = "link_extra_lib",
+    tags = ["__DONT_DEPEND_ON_DEF_PARSER__"],
+    deps = [
+        ":link_extra_libs",
+    ],
+)
+
 cc_library(
     name = "malloc",
     tags = ["__DONT_DEPEND_ON_DEF_PARSER__"],