Repack libgcc.a to only include required objects

Previous solution by using objcopy uses a quirky behaviour of the GNU
objcopy and there is no equivalent option in llvm-objcopy.

Instead of removing symbols, extract and repack libgcc to only include
required objects.

Bug: 142585047
Test: presubmit
Change-Id: I58af74c18838f797e481da38c3265f0624fddf99

4 files changed, 127 insertions, 87 deletions

diff --git a/Android.bp b/Android.bp
index 9962b624..fa9a0176 100644
--- a/Android.bp
+++ b/Android.bp
@@ -579,104 +579,21 @@ toolchain_library {
     arch: {
         arm: {
             src: "prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/lib/gcc/arm-linux-androideabi/4.9.x/libgcc.a",
-            strip: {
-                keep_symbols_list: [
-                    // unwind-arm.o
-                    "_Unwind_Complete",
-                    "_Unwind_DeleteException",
-                    "_Unwind_GetCFA",
-                    "_Unwind_VRS_Get",
-                    "_Unwind_VRS_Pop",
-                    "_Unwind_VRS_Set",
-                    "__aeabi_unwind_cpp_pr0",
-                    "__aeabi_unwind_cpp_pr1",
-                    "__aeabi_unwind_cpp_pr2",
-                    "__gnu_Unwind_Backtrace",
-                    "__gnu_Unwind_ForcedUnwind",
-                    "__gnu_Unwind_RaiseException",
-                    "__gnu_Unwind_Resume",
-                    "__gnu_Unwind_Resume_or_Rethrow",
-
-                    // libunwind.o
-                    "_Unwind_Backtrace",
-                    "_Unwind_ForcedUnwind",
-                    "_Unwind_RaiseException",
-                    "_Unwind_Resume",
-                    "_Unwind_Resume_or_Rethrow",
-                    "___Unwind_Backtrace",
-                    "___Unwind_ForcedUnwind",
-                    "___Unwind_RaiseException",
-                    "___Unwind_Resume",
-                    "___Unwind_Resume_or_Rethrow",
-                    "__gnu_Unwind_Restore_VFP",
-                    "__gnu_Unwind_Restore_VFP_D",
-                    "__gnu_Unwind_Restore_VFP_D_16_to_31",
-                    "__gnu_Unwind_Restore_WMMXC",
-                    "__gnu_Unwind_Restore_WMMXD",
-                    "__gnu_Unwind_Save_VFP",
-                    "__gnu_Unwind_Save_VFP_D",
-                    "__gnu_Unwind_Save_VFP_D_16_to_31",
-                    "__gnu_Unwind_Save_WMMXC",
-                    "__gnu_Unwind_Save_WMMXD",
-                    "__restore_core_regs",
-                    "restore_core_regs",
-
-                    // pr-support.o
-                    "_Unwind_GetDataRelBase",
-                    "_Unwind_GetLanguageSpecificData",
-                    "_Unwind_GetRegionStart",
-                    "_Unwind_GetTextRelBase",
-                    "__gnu_unwind_execute",
-                    "__gnu_unwind_frame",
-                ],
-            },
+            repack_objects_to_keep: ["unwind-arm.o", "libunwind.o", "pr-support.o"],
         },
         arm64: {
             src: "prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/lib/gcc/aarch64-linux-android/4.9.x/libgcc.a",
+            repack_objects_to_keep: ["unwind-dw2.o", "unwind-dw2-fde-dip.o"],
         },
         x86: {
             src: "prebuilts/gcc/linux-x86/x86/x86_64-linux-android-4.9/lib/gcc/x86_64-linux-android/4.9.x/32/libgcc.a",
-
+            repack_objects_to_keep: ["unwind-dw2.o", "unwind-dw2-fde-dip.o"],
         },
         x86_64: {
             src: "prebuilts/gcc/linux-x86/x86/x86_64-linux-android-4.9/lib/gcc/x86_64-linux-android/4.9.x/libgcc.a",
+            repack_objects_to_keep: ["unwind-dw2.o", "unwind-dw2-fde-dip.o"],
         },
     },
-    strip: {
-        keep_symbols_list: [
-            // unwind-dw2.o
-            "_Unwind_Backtrace",
-            "_Unwind_DeleteException",
-            "_Unwind_FindEnclosingFunction",
-            "_Unwind_ForcedUnwind",
-            "_Unwind_GetCFA",
-            "_Unwind_GetDataRelBase",
-            "_Unwind_GetGR",
-            "_Unwind_GetIP",
-            "_Unwind_GetIPInfo",
-            "_Unwind_GetLanguageSpecificData",
-            "_Unwind_GetRegionStart",
-            "_Unwind_GetTextRelBase",
-            "_Unwind_RaiseException",
-            "_Unwind_Resume",
-            "_Unwind_Resume_or_Rethrow",
-            "_Unwind_SetGR",
-            "_Unwind_SetIP",
-            "__frame_state_for",
-
-            // unwind-dw2-fde-dip.o
-            "_Unwind_Find_FDE",
-            "__deregister_frame",
-            "__deregister_frame_info",
-            "__deregister_frame_info_bases",
-            "__register_frame",
-            "__register_frame_info",
-            "__register_frame_info_bases",
-            "__register_frame_info_table",
-            "__register_frame_info_table_bases",
-            "__register_frame_table",
-        ],
-    },
 }
 
 toolchain_library {
diff --git a/cc/builder.go b/cc/builder.go
index 0760dd49..491ebc59 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -130,6 +130,17 @@ var (
 		},
 		"args", "crossCompile")
 
+	_ = pctx.SourcePathVariable("archiveRepackPath", "build/soong/scripts/archive_repack.sh")
+
+	archiveRepack = pctx.AndroidStaticRule("archiveRepack",
+		blueprint.RuleParams{
+			Depfile:     "${out}.d",
+			Deps:        blueprint.DepsGCC,
+			Command:     "CLANG_BIN=${config.ClangBin} $archiveRepackPath -i ${in} -o ${out} -d ${out}.d ${objects}",
+			CommandDeps: []string{"$archiveRepackPath"},
+		},
+		"objects")
+
 	emptyFile = pctx.AndroidStaticRule("emptyFile",
 		blueprint.RuleParams{
 			Command: "rm -f $out && touch $out",
@@ -866,6 +877,20 @@ func TransformCoverageFilesToZip(ctx android.ModuleContext,
 	return android.OptionalPath{}
 }
 
+func TransformArchiveRepack(ctx android.ModuleContext, inputFile android.Path,
+	outputFile android.WritablePath, objects []string) {
+
+	ctx.Build(pctx, android.BuildParams{
+		Rule:        archiveRepack,
+		Description: "Repack archive " + outputFile.Base(),
+		Output:      outputFile,
+		Input:       inputFile,
+		Args: map[string]string{
+			"objects": strings.Join(objects, " "),
+		},
+	})
+}
+
 func gccCmd(toolchain config.Toolchain, cmd string) string {
 	return filepath.Join(toolchain.GccRoot(), "bin", toolchain.GccTriple()+"-"+cmd)
 }
diff --git a/cc/toolchain_library.go b/cc/toolchain_library.go
index fef4508f..dfc6f767 100644
--- a/cc/toolchain_library.go
+++ b/cc/toolchain_library.go
@@ -29,6 +29,9 @@ func init() {
 type toolchainLibraryProperties struct {
 	// the prebuilt toolchain library, as a path from the top of the source tree
 	Src *string `android:"arch_variant"`
+
+	// Repack the archive with only the selected objects.
+	Repack_objects_to_keep []string `android:"arch_variant"`
 }
 
 type toolchainLibraryDecorator struct {
@@ -90,6 +93,14 @@ func (library *toolchainLibraryDecorator) link(ctx ModuleContext,
 		return outputFile
 	}
 
+	if library.Properties.Repack_objects_to_keep != nil {
+		fileName := ctx.ModuleName() + staticLibraryExtension
+		outputFile := android.PathForModuleOut(ctx, fileName)
+		TransformArchiveRepack(ctx, srcPath, outputFile, library.Properties.Repack_objects_to_keep)
+
+		return outputFile
+	}
+
 	return srcPath
 }
 
diff --git a/scripts/archive_repack.sh b/scripts/archive_repack.sh
new file mode 100755
index 00000000..f09372dd
--- /dev/null
+++ b/scripts/archive_repack.sh
@@ -0,0 +1,87 @@
+#!/bin/bash -e
+
+# Copyright 2019 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Script to extract and repack an archive with specified object files.
+# Inputs:
+#  Environment:
+#   CLANG_BIN: path to the clang bin directory
+#  Arguments:
+#   -i ${file}: input file
+#   -o ${file}: output file
+#   -d ${file}: deps file
+
+set -o pipefail
+
+OPTSTRING=d:i:o:
+
+usage() {
+    cat <<EOF
+Usage: archive_repack.sh [options] <objects to repack>
+
+OPTIONS:
+    -i <file>: input file
+    -o <file>: output file
+    -d <file>: deps file
+EOF
+    exit 1
+}
+
+while getopts $OPTSTRING opt; do
+    case "$opt" in
+        d) depsfile="${OPTARG}" ;;
+        i) infile="${OPTARG}" ;;
+        o) outfile="${OPTARG}" ;;
+        ?) usage ;;
+    esac
+done
+shift "$(($OPTIND -1))"
+
+if [ -z "${infile}" ]; then
+    echo "-i argument is required"
+    usage
+fi
+
+if [ -z "${outfile}" ]; then
+    echo "-o argument is required"
+    usage
+fi
+
+# Produce deps file
+if [ ! -z "${depsfile}" ]; then
+    cat <<EOF > "${depsfile}"
+${outfile}: ${infile} ${CLANG_BIN}/llvm-ar
+EOF
+fi
+
+# Get absolute path for outfile and llvm-ar.
+LLVM_AR="${PWD}/${CLANG_BIN}/llvm-ar"
+if [[ "$outfile" != /* ]]; then
+    outfile="${PWD}/${outfile}"
+fi
+
+tempdir="${outfile}.tmp"
+
+# Clean up any previous temporary files.
+rm -f "${outfile}"
+rm -rf "${tempdir}"
+
+# Do repack
+# We have to change working directory since ar only allows extracting to CWD.
+mkdir "${tempdir}"
+cp "${infile}" "${tempdir}/archive"
+cd "${tempdir}"
+"${LLVM_AR}" x "archive"
+"${LLVM_AR}" --format=gnu qc "${outfile}" "$@"