cc/builder.go

// Copyright 2015 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.

package cc

// This file generates the final rules for compiling all C/C++.  All properties related to
// compiling should have been translated into builderFlags or another argument to the Transform*
// functions.

import (
	"fmt"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"

	"github.com/google/blueprint"

	"android/soong/android"
	"android/soong/cc/config"
)

const (
	objectExtension        = ".o"
	staticLibraryExtension = ".a"
)

var (
	abiCheckAllowFlags = []string{
		"-allow-unreferenced-changes",
		"-allow-unreferenced-elf-symbol-changes",
	}
)

var (
	pctx = android.NewPackageContext("android/soong/cc")

	cc = pctx.AndroidGomaStaticRule("cc",
		blueprint.RuleParams{
			Depfile:     "${out}.d",
			Deps:        blueprint.DepsGCC,
			Command:     "$relPwd ${config.CcWrapper}$ccCmd -c $cFlags -MD -MF ${out}.d -o $out $in",
			CommandDeps: []string{"$ccCmd"},
		},
		"ccCmd", "cFlags")

	ld = pctx.AndroidStaticRule("ld",
		blueprint.RuleParams{
			Command: "$ldCmd ${crtBegin} @${out}.rsp " +
				"${libFlags} ${crtEnd} -o ${out} ${ldFlags}",
			CommandDeps:    []string{"$ldCmd"},
			Rspfile:        "${out}.rsp",
			RspfileContent: "${in}",
		},
		"ldCmd", "crtBegin", "libFlags", "crtEnd", "ldFlags")

	partialLd = pctx.AndroidStaticRule("partialLd",
		blueprint.RuleParams{
			// Without -no-pie, clang 7.0 adds -pie to link Android files,
			// but -r and -pie cannot be used together.
			Command:     "$ldCmd -nostdlib -no-pie -Wl,-r ${in} -o ${out} ${ldFlags}",
			CommandDeps: []string{"$ldCmd"},
		},
		"ldCmd", "ldFlags")

	ar = pctx.AndroidStaticRule("ar",
		blueprint.RuleParams{
			Command:        "rm -f ${out} && $arCmd $arFlags $out @${out}.rsp",
			CommandDeps:    []string{"$arCmd"},
			Rspfile:        "${out}.rsp",
			RspfileContent: "${in}",
		},
		"arCmd", "arFlags")

	darwinAr = pctx.AndroidStaticRule("darwinAr",
		blueprint.RuleParams{
			Command:     "rm -f ${out} && ${config.MacArPath} $arFlags $out $in",
			CommandDeps: []string{"${config.MacArPath}"},
		},
		"arFlags")

	darwinAppendAr = pctx.AndroidStaticRule("darwinAppendAr",
		blueprint.RuleParams{
			Command:     "cp -f ${inAr} ${out}.tmp && ${config.MacArPath} $arFlags ${out}.tmp $in && mv ${out}.tmp ${out}",
			CommandDeps: []string{"${config.MacArPath}", "${inAr}"},
		},
		"arFlags", "inAr")

	darwinStrip = pctx.AndroidStaticRule("darwinStrip",
		blueprint.RuleParams{
			Command:     "${config.MacStripPath} -u -r -o $out $in",
			CommandDeps: []string{"${config.MacStripPath}"},
		})

	prefixSymbols = pctx.AndroidStaticRule("prefixSymbols",
		blueprint.RuleParams{
			Command:     "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}",
			CommandDeps: []string{"$objcopyCmd"},
		},
		"objcopyCmd", "prefix")

	_ = pctx.SourcePathVariable("stripPath", "build/soong/scripts/strip.sh")
	_ = pctx.SourcePathVariable("xzCmd", "prebuilts/build-tools/${config.HostPrebuiltTag}/bin/xz")

	strip = pctx.AndroidStaticRule("strip",
		blueprint.RuleParams{
			Depfile:     "${out}.d",
			Deps:        blueprint.DepsGCC,
			Command:     "CROSS_COMPILE=$crossCompile XZ=$xzCmd CLANG_BIN=${config.ClangBin} $stripPath ${args} -i ${in} -o ${out} -d ${out}.d",
			CommandDeps: []string{"$stripPath", "$xzCmd"},
		},
		"args", "crossCompile")

	emptyFile = pctx.AndroidStaticRule("emptyFile",
		blueprint.RuleParams{
			Command: "rm -f $out && touch $out",
		})

	_ = pctx.SourcePathVariable("tocPath", "build/soong/scripts/toc.sh")

	toc = pctx.AndroidStaticRule("toc",
		blueprint.RuleParams{
			Depfile:     "${out}.d",
			Deps:        blueprint.DepsGCC,
			Command:     "CROSS_COMPILE=$crossCompile $tocPath $format -i ${in} -o ${out} -d ${out}.d",
			CommandDeps: []string{"$tocPath"},
			Restat:      true,
		},
		"crossCompile", "format")

	clangTidy = pctx.AndroidStaticRule("clangTidy",
		blueprint.RuleParams{
			Command:     "rm -f $out && CLANG_TIDY=${config.ClangBin}/clang-tidy ${config.ClangTidyShellPath} $tidyFlags $in -- $cFlags && touch $out",
			CommandDeps: []string{"${config.ClangBin}/clang-tidy", "${config.ClangTidyShellPath}"},
		},
		"cFlags", "tidyFlags")

	_ = pctx.SourcePathVariable("yasmCmd", "prebuilts/misc/${config.HostPrebuiltTag}/yasm/yasm")

	yasm = pctx.AndroidStaticRule("yasm",
		blueprint.RuleParams{
			Command:     "$yasmCmd $asFlags -o $out $in && $yasmCmd $asFlags -M $in >$out.d",
			CommandDeps: []string{"$yasmCmd"},
			Depfile:     "$out.d",
			Deps:        blueprint.DepsGCC,
		},
		"asFlags")

	windres = pctx.AndroidStaticRule("windres",
		blueprint.RuleParams{
			Command:     "$windresCmd $flags -I$$(dirname $in) -i $in -o $out",
			CommandDeps: []string{"$windresCmd"},
		},
		"windresCmd", "flags")

	_ = pctx.SourcePathVariable("sAbiDumper", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-dumper")

	// -w has been added since header-abi-dumper does not need to produce any sort of diagnostic information.
	sAbiDump = pctx.AndroidStaticRule("sAbiDump",
		blueprint.RuleParams{
			Command:     "rm -f $out && $sAbiDumper -o ${out} $in $exportDirs -- $cFlags -w -isystem prebuilts/clang-tools/${config.HostPrebuiltTag}/clang-headers",
			CommandDeps: []string{"$sAbiDumper"},
		},
		"cFlags", "exportDirs")

	_ = pctx.SourcePathVariable("sAbiLinker", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-linker")

	sAbiLink = pctx.AndroidStaticRule("sAbiLink",
		blueprint.RuleParams{
			Command:        "$sAbiLinker -o ${out} $symbolFilter -arch $arch  $exportedHeaderFlags @${out}.rsp ",
			CommandDeps:    []string{"$sAbiLinker"},
			Rspfile:        "${out}.rsp",
			RspfileContent: "${in}",
		},
		"symbolFilter", "arch", "exportedHeaderFlags")

	_ = pctx.SourcePathVariable("sAbiDiffer", "prebuilts/clang-tools/${config.HostPrebuiltTag}/bin/header-abi-diff")

	sAbiDiff = pctx.AndroidRuleFunc("sAbiDiff",
		func(ctx android.PackageRuleContext) blueprint.RuleParams {
			// TODO(b/78139997): Add -check-all-apis back
			commandStr := "($sAbiDiffer $allowFlags -lib $libName -arch $arch -o ${out} -new $in -old $referenceDump)"
			commandStr += "|| (echo ' ---- Please update abi references by running $$ANDROID_BUILD_TOP/development/vndk/tools/header-checker/utils/create_reference_dumps.py -l ${libName} ----'"
			commandStr += " && (mkdir -p $$DIST_DIR/abidiffs && cp ${out} $$DIST_DIR/abidiff/)"
			commandStr += " && exit 1)"
			return blueprint.RuleParams{
				Command:     commandStr,
				CommandDeps: []string{"$sAbiDiffer"},
			}
		},
		"allowFlags", "referenceDump", "libName", "arch")

	unzipRefSAbiDump = pctx.AndroidStaticRule("unzipRefSAbiDump",
		blueprint.RuleParams{
			Command: "gunzip -c $in > $out",
		})
)

func init() {
	// We run gcc/clang with PWD=/proc/self/cwd to remove $TOP from the
	// debug output. That way two builds in two different directories will
	// create the same output.
	if runtime.GOOS != "darwin" {
		pctx.StaticVariable("relPwd", "PWD=/proc/self/cwd")
	} else {
		// Darwin doesn't have /proc
		pctx.StaticVariable("relPwd", "")
	}
}

type builderFlags struct {
	globalFlags     string
	arFlags         string
	asFlags         string
	cFlags          string
	toolingCFlags   string // A separate set of cFlags for clang LibTooling tools
	toolingCppFlags string // A separate set of cppFlags for clang LibTooling tools
	conlyFlags      string
	cppFlags        string
	ldFlags         string
	libFlags        string
	yaccFlags       string
	protoFlags      string
	protoOutParams  string
	tidyFlags       string
	sAbiFlags       string
	yasmFlags       string
	aidlFlags       string
	rsFlags         string
	toolchain       config.Toolchain
	tidy            bool
	coverage        bool
	sAbiDump        bool
	protoRoot       bool

	systemIncludeFlags string

	groupStaticLibs bool

	stripKeepSymbols       bool
	stripKeepMiniDebugInfo bool
	stripAddGnuDebuglink   bool
	stripUseLlvmStrip      bool
}

type Objects struct {
	objFiles      android.Paths
	tidyFiles     android.Paths
	coverageFiles android.Paths
	sAbiDumpFiles android.Paths
}

func (a Objects) Copy() Objects {
	return Objects{
		objFiles:      append(android.Paths{}, a.objFiles...),
		tidyFiles:     append(android.Paths{}, a.tidyFiles...),
		coverageFiles: append(android.Paths{}, a.coverageFiles...),
		sAbiDumpFiles: append(android.Paths{}, a.sAbiDumpFiles...),
	}
}

func (a Objects) Append(b Objects) Objects {
	return Objects{
		objFiles:      append(a.objFiles, b.objFiles...),
		tidyFiles:     append(a.tidyFiles, b.tidyFiles...),
		coverageFiles: append(a.coverageFiles, b.coverageFiles...),
		sAbiDumpFiles: append(a.sAbiDumpFiles, b.sAbiDumpFiles...),
	}
}

// Generate rules for compiling multiple .c, .cpp, or .S files to individual .o files
func TransformSourceToObj(ctx android.ModuleContext, subdir string, srcFiles android.Paths,
	flags builderFlags, pathDeps android.Paths, cFlagsDeps android.Paths) Objects {

	objFiles := make(android.Paths, len(srcFiles))
	var tidyFiles android.Paths
	if flags.tidy {
		tidyFiles = make(android.Paths, 0, len(srcFiles))
	}
	var coverageFiles android.Paths
	if flags.coverage {
		coverageFiles = make(android.Paths, 0, len(srcFiles))
	}

	commonFlags := strings.Join([]string{
		flags.globalFlags,
		flags.systemIncludeFlags,
	}, " ")

	toolingCflags := strings.Join([]string{
		commonFlags,
		flags.toolingCFlags,
		flags.conlyFlags,
	}, " ")

	cflags := strings.Join([]string{
		commonFlags,
		flags.cFlags,
		flags.conlyFlags,
	}, " ")

	toolingCppflags := strings.Join([]string{
		commonFlags,
		flags.toolingCFlags,
		flags.toolingCppFlags,
	}, " ")

	cppflags := strings.Join([]string{
		commonFlags,
		flags.cFlags,
		flags.cppFlags,
	}, " ")

	asflags := strings.Join([]string{
		commonFlags,
		flags.asFlags,
	}, " ")

	var sAbiDumpFiles android.Paths
	if flags.sAbiDump {
		sAbiDumpFiles = make(android.Paths, 0, len(srcFiles))
	}

	cflags += " ${config.NoOverrideClangGlobalCflags}"
	toolingCflags += " ${config.NoOverrideClangGlobalCflags}"
	cppflags += " ${config.NoOverrideClangGlobalCflags}"
	toolingCppflags += " ${config.NoOverrideClangGlobalCflags}"

	for i, srcFile := range srcFiles {
		objFile := android.ObjPathWithExt(ctx, subdir, srcFile, "o")

		objFiles[i] = objFile

		switch srcFile.Ext() {
		case ".asm":
			ctx.Build(pctx, android.BuildParams{
				Rule:        yasm,
				Description: "yasm " + srcFile.Rel(),
				Output:      objFile,
				Input:       srcFile,
				Implicits:   cFlagsDeps,
				OrderOnly:   pathDeps,
				Args: map[string]string{
					"asFlags": flags.yasmFlags,
				},
			})
			continue
		case ".rc":
			ctx.Build(pctx, android.BuildParams{
				Rule:        windres,
				Description: "windres " + srcFile.Rel(),
				Output:      objFile,
				Input:       srcFile,
				Implicits:   cFlagsDeps,
				OrderOnly:   pathDeps,
				Args: map[string]string{
					"windresCmd": gccCmd(flags.toolchain, "windres"),
					"flags":      flags.toolchain.WindresFlags(),
				},
			})
			continue
		}

		var moduleCflags string
		var moduleToolingCflags string
		var ccCmd string
		tidy := flags.tidy
		coverage := flags.coverage
		dump := flags.sAbiDump

		switch srcFile.Ext() {
		case ".S", ".s":
			ccCmd = "clang"
			moduleCflags = asflags
			tidy = false
			coverage = false
			dump = false
		case ".c":
			ccCmd = "clang"
			moduleCflags = cflags
			moduleToolingCflags = toolingCflags
		case ".cpp", ".cc", ".mm":
			ccCmd = "clang++"
			moduleCflags = cppflags
			moduleToolingCflags = toolingCppflags
		default:
			ctx.ModuleErrorf("File %s has unknown extension", srcFile)
			continue
		}

		ccDesc := ccCmd

		ccCmd = "${config.ClangBin}/" + ccCmd

		var implicitOutputs android.WritablePaths
		if coverage {
			gcnoFile := android.ObjPathWithExt(ctx, subdir, srcFile, "gcno")
			implicitOutputs = append(implicitOutputs, gcnoFile)
			coverageFiles = append(coverageFiles, gcnoFile)
		}

		ctx.Build(pctx, android.BuildParams{
			Rule:            cc,
			Description:     ccDesc + " " + srcFile.Rel(),
			Output:          objFile,
			ImplicitOutputs: implicitOutputs,
			Input:           srcFile,
			Implicits:       cFlagsDeps,
			OrderOnly:       pathDeps,
			Args: map[string]string{
				"cFlags": moduleCflags,
				"ccCmd":  ccCmd,
			},
		})

		if tidy {
			tidyFile := android.ObjPathWithExt(ctx, subdir, srcFile, "tidy")
			tidyFiles = append(tidyFiles, tidyFile)

			ctx.Build(pctx, android.BuildParams{
				Rule:        clangTidy,
				Description: "clang-tidy " + srcFile.Rel(),
				Output:      tidyFile,
				Input:       srcFile,
				// We must depend on objFile, since clang-tidy doesn't
				// support exporting dependencies.
				Implicit: objFile,
				Args: map[string]string{
					"cFlags":    moduleToolingCflags,
					"tidyFlags": flags.tidyFlags,
				},
			})
		}

		if dump {
			sAbiDumpFile := android.ObjPathWithExt(ctx, subdir, srcFile, "sdump")
			sAbiDumpFiles = append(sAbiDumpFiles, sAbiDumpFile)

			ctx.Build(pctx, android.BuildParams{
				Rule:        sAbiDump,
				Description: "header-abi-dumper " + srcFile.Rel(),
				Output:      sAbiDumpFile,
				Input:       srcFile,
				Implicit:    objFile,
				Args: map[string]string{
					"cFlags":     moduleToolingCflags,
					"exportDirs": flags.sAbiFlags,
				},
			})
		}

	}

	return Objects{
		objFiles:      objFiles,
		tidyFiles:     tidyFiles,
		coverageFiles: coverageFiles,
		sAbiDumpFiles: sAbiDumpFiles,
	}
}

// Generate a rule for compiling multiple .o files to a static library (.a)
func TransformObjToStaticLib(ctx android.ModuleContext, objFiles android.Paths,
	flags builderFlags, outputFile android.ModuleOutPath, deps android.Paths) {

	if ctx.Darwin() {
		transformDarwinObjToStaticLib(ctx, objFiles, flags, outputFile, deps)
		return
	}

	arCmd := "${config.ClangBin}/llvm-ar"
	arFlags := "crsD"
	if !ctx.Darwin() {
		arFlags += " -format=gnu"
	}
	if flags.arFlags != "" {
		arFlags += " " + flags.arFlags
	}

	ctx.Build(pctx, android.BuildParams{
		Rule:        ar,
		Description: "static link " + outputFile.Base(),
		Output:      outputFile,
		Inputs:      objFiles,
		Implicits:   deps,
		Args: map[string]string{
			"arFlags": arFlags,
			"arCmd":   arCmd,
		},
	})
}

// Generate a rule for compiling multiple .o files to a static library (.a) on
// darwin.  The darwin ar tool doesn't support @file for list files, and has a
// very small command line length limit, so we have to split the ar into multiple
// steps, each appending to the previous one.
func transformDarwinObjToStaticLib(ctx android.ModuleContext, objFiles android.Paths,
	flags builderFlags, outputFile android.ModuleOutPath, deps android.Paths) {

	arFlags := "cqs"

	if len(objFiles) == 0 {
		dummy := android.PathForModuleOut(ctx, "dummy"+objectExtension)
		dummyAr := android.PathForModuleOut(ctx, "dummy"+staticLibraryExtension)

		ctx.Build(pctx, android.BuildParams{
			Rule:        emptyFile,
			Description: "empty object file",
			Output:      dummy,
			Implicits:   deps,
		})

		ctx.Build(pctx, android.BuildParams{
			Rule:        darwinAr,
			Description: "empty static archive",
			Output:      dummyAr,
			Input:       dummy,
			Args: map[string]string{
				"arFlags": arFlags,
			},
		})

		ctx.Build(pctx, android.BuildParams{
			Rule:        darwinAppendAr,
			Description: "static link " + outputFile.Base(),
			Output:      outputFile,
			Input:       dummy,
			Args: map[string]string{
				"arFlags": "d",
				"inAr":    dummyAr.String(),
			},
		})

		return
	}

	// ARG_MAX on darwin is 262144, use half that to be safe
	objFilesLists, err := splitListForSize(objFiles, 131072)
	if err != nil {
		ctx.ModuleErrorf("%s", err.Error())
	}

	var in, out android.WritablePath
	for i, l := range objFilesLists {
		in = out
		out = outputFile
		if i != len(objFilesLists)-1 {
			out = android.PathForModuleOut(ctx, outputFile.Base()+strconv.Itoa(i))
		}

		build := android.BuildParams{
			Rule:        darwinAr,
			Description: "static link " + out.Base(),
			Output:      out,
			Inputs:      l,
			Implicits:   deps,
			Args: map[string]string{
				"arFlags": arFlags,
			},
		}
		if i != 0 {
			build.Rule = darwinAppendAr
			build.Args["inAr"] = in.String()
		}
		ctx.Build(pctx, build)
	}
}

// Generate a rule for compiling multiple .o files, plus static libraries, whole static libraries,
// and shared libraries, to a shared library (.so) or dynamic executable
func TransformObjToDynamicBinary(ctx android.ModuleContext,
	objFiles, sharedLibs, staticLibs, lateStaticLibs, wholeStaticLibs, deps android.Paths,
	crtBegin, crtEnd android.OptionalPath, groupLate bool, flags builderFlags, outputFile android.WritablePath) {

	ldCmd := "${config.ClangBin}/clang++"

	var libFlagsList []string

	if len(flags.libFlags) > 0 {
		libFlagsList = append(libFlagsList, flags.libFlags)
	}

	if len(wholeStaticLibs) > 0 {
		if ctx.Host() && ctx.Darwin() {
			libFlagsList = append(libFlagsList, android.JoinWithPrefix(wholeStaticLibs.Strings(), "-force_load "))
		} else {
			libFlagsList = append(libFlagsList, "-Wl,--whole-archive ")
			libFlagsList = append(libFlagsList, wholeStaticLibs.Strings()...)
			libFlagsList = append(libFlagsList, "-Wl,--no-whole-archive ")
		}
	}

	if flags.groupStaticLibs && !ctx.Darwin() && len(staticLibs) > 0 {
		libFlagsList = append(libFlagsList, "-Wl,--start-group")
	}
	libFlagsList = append(libFlagsList, staticLibs.Strings()...)
	if flags.groupStaticLibs && !ctx.Darwin() && len(staticLibs) > 0 {
		libFlagsList = append(libFlagsList, "-Wl,--end-group")
	}

	if groupLate && !ctx.Darwin() && len(lateStaticLibs) > 0 {
		libFlagsList = append(libFlagsList, "-Wl,--start-group")
	}
	libFlagsList = append(libFlagsList, lateStaticLibs.Strings()...)
	if groupLate && !ctx.Darwin() && len(lateStaticLibs) > 0 {
		libFlagsList = append(libFlagsList, "-Wl,--end-group")
	}

	for _, lib := range sharedLibs {
		libFlagsList = append(libFlagsList, lib.String())
	}

	deps = append(deps, staticLibs...)
	deps = append(deps, lateStaticLibs...)
	deps = append(deps, wholeStaticLibs...)
	if crtBegin.Valid() {
		deps = append(deps, crtBegin.Path(), crtEnd.Path())
	}

	ctx.Build(pctx, android.BuildParams{
		Rule:        ld,
		Description: "link " + outputFile.Base(),
		Output:      outputFile,
		Inputs:      objFiles,
		Implicits:   deps,
		Args: map[string]string{
			"ldCmd":    ldCmd,
			"crtBegin": crtBegin.String(),
			"libFlags": strings.Join(libFlagsList, " "),
			"ldFlags":  flags.ldFlags,
			"crtEnd":   crtEnd.String(),
		},
	})
}

// Generate a rule to combine .dump sAbi dump files from multiple source files
// into a single .ldump sAbi dump file
func TransformDumpToLinkedDump(ctx android.ModuleContext, sAbiDumps android.Paths, soFile android.Path,
	baseName, exportedHeaderFlags string) android.OptionalPath {
	outputFile := android.PathForModuleOut(ctx, baseName+".lsdump")
	sabiLock.Lock()
	lsdumpPaths = append(lsdumpPaths, outputFile.String())
	sabiLock.Unlock()
	symbolFilterStr := "-so " + soFile.String()
	ctx.Build(pctx, android.BuildParams{
		Rule:        sAbiLink,
		Description: "header-abi-linker " + outputFile.Base(),
		Output:      outputFile,
		Inputs:      sAbiDumps,
		Implicit:    soFile,
		Args: map[string]string{
			"symbolFilter":        symbolFilterStr,
			"arch":                ctx.Arch().ArchType.Name,
			"exportedHeaderFlags": exportedHeaderFlags,
		},
	})
	return android.OptionalPathForPath(outputFile)
}

func UnzipRefDump(ctx android.ModuleContext, zippedRefDump android.Path, baseName string) android.Path {
	outputFile := android.PathForModuleOut(ctx, baseName+"_ref.lsdump")
	ctx.Build(pctx, android.BuildParams{
		Rule:        unzipRefSAbiDump,
		Description: "gunzip" + outputFile.Base(),
		Output:      outputFile,
		Input:       zippedRefDump,
	})
	return outputFile
}

func SourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path,
	baseName, exportedHeaderFlags string, isVndkExt bool) android.OptionalPath {

	outputFile := android.PathForModuleOut(ctx, baseName+".abidiff")
	libName := strings.TrimSuffix(baseName, filepath.Ext(baseName))
	localAbiCheckAllowFlags := append([]string(nil), abiCheckAllowFlags...)
	if exportedHeaderFlags == "" {
		localAbiCheckAllowFlags = append(localAbiCheckAllowFlags, "-advice-only")
	}
	if inList(libName, llndkLibraries) {
		localAbiCheckAllowFlags = append(localAbiCheckAllowFlags, "-consider-opaque-types-different")
	}
	if isVndkExt {
		localAbiCheckAllowFlags = append(localAbiCheckAllowFlags, "-allow-extensions")
	}

	ctx.Build(pctx, android.BuildParams{
		Rule:        sAbiDiff,
		Description: "header-abi-diff " + outputFile.Base(),
		Output:      outputFile,
		Input:       inputDump,
		Implicit:    referenceDump,
		Args: map[string]string{
			"referenceDump": referenceDump.String(),
			"libName":       libName,
			"arch":          ctx.Arch().ArchType.Name,
			"allowFlags":    strings.Join(localAbiCheckAllowFlags, " "),
		},
	})
	return android.OptionalPathForPath(outputFile)
}

// Generate a rule for extracting a table of contents from a shared library (.so)
func TransformSharedObjectToToc(ctx android.ModuleContext, inputFile android.Path,
	outputFile android.WritablePath, flags builderFlags) {

	var format string
	var crossCompile string
	if ctx.Darwin() {
		format = "--macho"
		crossCompile = "${config.MacToolPath}"
	} else if ctx.Windows() {
		format = "--pe"
		crossCompile = gccCmd(flags.toolchain, "")
	} else {
		format = "--elf"
		crossCompile = gccCmd(flags.toolchain, "")
	}

	ctx.Build(pctx, android.BuildParams{
		Rule:        toc,
		Description: "generate toc " + inputFile.Base(),
		Output:      outputFile,
		Input:       inputFile,
		Args: map[string]string{
			"crossCompile": crossCompile,
			"format":       format,
		},
	})
}

// Generate a rule for compiling multiple .o files to a .o using ld partial linking
func TransformObjsToObj(ctx android.ModuleContext, objFiles android.Paths,
	flags builderFlags, outputFile android.WritablePath) {

	ldCmd := "${config.ClangBin}/clang++"

	ctx.Build(pctx, android.BuildParams{
		Rule:        partialLd,
		Description: "link " + outputFile.Base(),
		Output:      outputFile,
		Inputs:      objFiles,
		Args: map[string]string{
			"ldCmd":   ldCmd,
			"ldFlags": flags.ldFlags,
		},
	})
}

// Generate a rule for runing objcopy --prefix-symbols on a binary
func TransformBinaryPrefixSymbols(ctx android.ModuleContext, prefix string, inputFile android.Path,
	flags builderFlags, outputFile android.WritablePath) {

	objcopyCmd := gccCmd(flags.toolchain, "objcopy")

	ctx.Build(pctx, android.BuildParams{
		Rule:        prefixSymbols,
		Description: "prefix symbols " + outputFile.Base(),
		Output:      outputFile,
		Input:       inputFile,
		Args: map[string]string{
			"objcopyCmd": objcopyCmd,
			"prefix":     prefix,
		},
	})
}

func TransformStrip(ctx android.ModuleContext, inputFile android.Path,
	outputFile android.WritablePath, flags builderFlags) {

	crossCompile := gccCmd(flags.toolchain, "")
	args := ""
	if flags.stripAddGnuDebuglink {
		args += " --add-gnu-debuglink"
	}
	if flags.stripKeepMiniDebugInfo {
		args += " --keep-mini-debug-info"
	}
	if flags.stripKeepSymbols {
		args += " --keep-symbols"
	}
	if flags.stripUseLlvmStrip {
		args += " --use-llvm-strip"
	}

	ctx.Build(pctx, android.BuildParams{
		Rule:        strip,
		Description: "strip " + outputFile.Base(),
		Output:      outputFile,
		Input:       inputFile,
		Args: map[string]string{
			"crossCompile": crossCompile,
			"args":         args,
		},
	})
}

func TransformDarwinStrip(ctx android.ModuleContext, inputFile android.Path,
	outputFile android.WritablePath) {

	ctx.Build(pctx, android.BuildParams{
		Rule:        darwinStrip,
		Description: "strip " + outputFile.Base(),
		Output:      outputFile,
		Input:       inputFile,
	})
}

func TransformCoverageFilesToLib(ctx android.ModuleContext,
	inputs Objects, flags builderFlags, baseName string) android.OptionalPath {

	if len(inputs.coverageFiles) > 0 {
		outputFile := android.PathForModuleOut(ctx, baseName+".gcnodir")

		TransformObjToStaticLib(ctx, inputs.coverageFiles, flags, outputFile, nil)

		return android.OptionalPathForPath(outputFile)
	}

	return android.OptionalPath{}
}

func gccCmd(toolchain config.Toolchain, cmd string) string {
	return filepath.Join(toolchain.GccRoot(), "bin", toolchain.GccTriple()+"-"+cmd)
}

func splitListForSize(list android.Paths, limit int) (lists []android.Paths, err error) {
	var i int

	start := 0
	bytes := 0
	for i = range list {
		l := len(list[i].String())
		if l > limit {
			return nil, fmt.Errorf("list element greater than size limit (%d)", limit)
		}
		if bytes+l > limit {
			lists = append(lists, list[start:i])
			start = i
			bytes = 0
		}
		bytes += l + 1 // count a space between each list element
	}

	lists = append(lists, list[start:])

	totalLen := 0
	for _, l := range lists {
		totalLen += len(l)
	}
	if totalLen != len(list) {
		panic(fmt.Errorf("Failed breaking up list, %d != %d", len(list), totalLen))
	}
	return lists, nil
}