// 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 ( 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"}, Description: "cc $out", }, "ccCmd", "cFlags") ld = pctx.AndroidStaticRule("ld", blueprint.RuleParams{ Command: "$ldCmd ${crtBegin} @${out}.rsp " + "${libFlags} ${crtEnd} -o ${out} ${ldFlags}", CommandDeps: []string{"$ldCmd"}, Description: "ld $out", Rspfile: "${out}.rsp", RspfileContent: "${in}", }, "ldCmd", "crtBegin", "libFlags", "crtEnd", "ldFlags") partialLd = pctx.AndroidStaticRule("partialLd", blueprint.RuleParams{ Command: "$ldCmd -nostdlib -Wl,-r ${in} -o ${out} ${ldFlags}", CommandDeps: []string{"$ldCmd"}, Description: "partialLd $out", }, "ldCmd", "ldFlags") ar = pctx.AndroidStaticRule("ar", blueprint.RuleParams{ Command: "rm -f ${out} && $arCmd $arFlags $out @${out}.rsp", CommandDeps: []string{"$arCmd"}, Description: "ar $out", Rspfile: "${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}"}, Description: "ar $out", }, "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}"}, Description: "ar $out", }, "arFlags", "inAr") darwinStrip = pctx.AndroidStaticRule("darwinStrip", blueprint.RuleParams{ Command: "${config.MacStripPath} -u -r -o $out $in", CommandDeps: []string{"${config.MacStripPath}"}, Description: "strip $out", }) prefixSymbols = pctx.AndroidStaticRule("prefixSymbols", blueprint.RuleParams{ Command: "$objcopyCmd --prefix-symbols=${prefix} ${in} ${out}", CommandDeps: []string{"$objcopyCmd"}, Description: "prefixSymbols $out", }, "objcopyCmd", "prefix") _ = pctx.SourcePathVariable("stripPath", "build/soong/scripts/strip.sh") strip = pctx.AndroidStaticRule("strip", blueprint.RuleParams{ Depfile: "${out}.d", Deps: blueprint.DepsGCC, Command: "CROSS_COMPILE=$crossCompile $stripPath ${args} -i ${in} -o ${out} -d ${out}.d", CommandDeps: []string{"$stripPath"}, Description: "strip $out", }, "args", "crossCompile") emptyFile = pctx.AndroidStaticRule("emptyFile", blueprint.RuleParams{ Command: "rm -f $out && touch $out", Description: "empty file $out", }) _ = pctx.SourcePathVariable("copyGccLibPath", "build/soong/scripts/copygcclib.sh") copyGccLib = pctx.AndroidStaticRule("copyGccLib", blueprint.RuleParams{ Depfile: "${out}.d", Deps: blueprint.DepsGCC, Command: "$copyGccLibPath $out $ccCmd $cFlags -print-file-name=${libName}", CommandDeps: []string{"$copyGccLibPath", "$ccCmd"}, Description: "copy gcc $out", }, "ccCmd", "cFlags", "libName") _ = pctx.SourcePathVariable("tocPath", "build/soong/scripts/toc.sh") toc = pctx.AndroidStaticRule("toc", blueprint.RuleParams{ Depfile: "${out}.d", Deps: blueprint.DepsGCC, Command: "CROSS_COMPILE=$crossCompile $tocPath -i ${in} -o ${out} -d ${out}.d", CommandDeps: []string{"$tocPath"}, Restat: true, }, "crossCompile") clangTidy = pctx.AndroidStaticRule("clangTidy", blueprint.RuleParams{ Command: "rm -f $out && ${config.ClangBin}/clang-tidy $tidyFlags $in -- $cFlags && touch $out", CommandDeps: []string{"${config.ClangBin}/clang-tidy"}, Description: "tidy $out", }, "cFlags", "tidyFlags") _ = pctx.SourcePathVariable("yasmCmd", "prebuilts/misc/${config.HostPrebuiltTag}/yasm/yasm") yasm = pctx.AndroidStaticRule("yasm", blueprint.RuleParams{ Command: "$yasmCmd $asFlags -o $out $in", CommandDeps: []string{"$yasmCmd"}, Description: "yasm $out", }, "asFlags") _ = pctx.SourcePathVariable("sAbiDumper", "prebuilts/build-tools/${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 ${config.RSIncludePath}", CommandDeps: []string{"$sAbiDumper"}, Description: "header-abi-dumper $in -o $out $exportDirs", }, "cFlags", "exportDirs") _ = pctx.SourcePathVariable("sAbiLinker", "prebuilts/build-tools/${config.HostPrebuiltTag}/bin/header-abi-linker") sAbiLink = pctx.AndroidStaticRule("sAbiLink", blueprint.RuleParams{ Command: "$sAbiLinker -o ${out} $symbolFile -arch $arch -api $api $exportedHeaderFlags @${out}.rsp ", CommandDeps: []string{"$sAbiLinker"}, Description: "header-abi-linker $in -o $out", Rspfile: "${out}.rsp", RspfileContent: "${in}", }, "symbolFile", "arch", "api", "exportedHeaderFlags") _ = pctx.SourcePathVariable("sAbiDiffer", "prebuilts/build-tools/${config.HostPrebuiltTag}/bin/header-abi-diff") // Abidiff check turned on in advice-only mode. Builds will not fail on abi incompatibilties / extensions. sAbiDiff = pctx.AndroidStaticRule("sAbiDiff", blueprint.RuleParams{ Command: "$sAbiDiffer -lib $libName -arch $arch -advice-only -o ${out} -new $in -old $referenceDump", CommandDeps: []string{"$sAbiDiffer"}, Description: "header-abi-diff -o ${out} -new $in -old $referenceDump", }, "referenceDump", "libName", "arch") unzipRefSAbiDump = pctx.AndroidStaticRule("unzipRefSAbiDump", blueprint.RuleParams{ Command: "gunzip -c $in > $out", Description: "gunzip $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 conlyFlags string cppFlags string ldFlags string libFlags string yaccFlags string protoFlags string tidyFlags string sAbiFlags string yasmFlags string aidlFlags string toolchain config.Toolchain clang bool tidy bool coverage bool sAbiDump bool systemIncludeFlags string groupStaticLibs bool stripKeepSymbols bool stripKeepMiniDebugInfo bool stripAddGnuDebuglink 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, deps android.Paths) Objects { objFiles := make(android.Paths, len(srcFiles)) var tidyFiles android.Paths if flags.tidy && flags.clang { tidyFiles = make(android.Paths, 0, len(srcFiles)) } var coverageFiles android.Paths if flags.coverage { coverageFiles = make(android.Paths, 0, len(srcFiles)) } cflags := strings.Join([]string{ flags.globalFlags, flags.systemIncludeFlags, flags.cFlags, flags.conlyFlags, }, " ") cppflags := strings.Join([]string{ flags.globalFlags, flags.systemIncludeFlags, flags.cFlags, flags.cppFlags, }, " ") asflags := strings.Join([]string{ flags.globalFlags, flags.systemIncludeFlags, flags.asFlags, }, " ") var sAbiDumpFiles android.Paths if flags.sAbiDump && flags.clang { sAbiDumpFiles = make(android.Paths, 0, len(srcFiles)) } if flags.clang { cflags += " ${config.NoOverrideClangGlobalCflags}" cppflags += " ${config.NoOverrideClangGlobalCflags}" } else { cflags += " ${config.NoOverrideGlobalCflags}" cppflags += " ${config.NoOverrideGlobalCflags}" } for i, srcFile := range srcFiles { objFile := android.ObjPathWithExt(ctx, subdir, srcFile, "o") objFiles[i] = objFile if srcFile.Ext() == ".asm" { ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: yasm, Output: objFile, Input: srcFile, OrderOnly: deps, Args: map[string]string{ "asFlags": flags.yasmFlags, }, }) continue } var moduleCflags string var ccCmd string tidy := flags.tidy && flags.clang coverage := flags.coverage dump := flags.sAbiDump && flags.clang switch srcFile.Ext() { case ".S", ".s": ccCmd = "gcc" moduleCflags = asflags tidy = false coverage = false dump = false case ".c": ccCmd = "gcc" moduleCflags = cflags case ".cpp", ".cc", ".mm": ccCmd = "g++" moduleCflags = cppflags default: ctx.ModuleErrorf("File %s has unknown extension", srcFile) continue } if flags.clang { switch ccCmd { case "gcc": ccCmd = "clang" case "g++": ccCmd = "clang++" default: panic("unrecoginzied ccCmd") } ccCmd = "${config.ClangBin}/" + ccCmd } else { ccCmd = gccCmd(flags.toolchain, ccCmd) } var implicitOutputs android.WritablePaths if coverage { gcnoFile := android.ObjPathWithExt(ctx, subdir, srcFile, "gcno") implicitOutputs = append(implicitOutputs, gcnoFile) coverageFiles = append(coverageFiles, gcnoFile) } ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: cc, Output: objFile, ImplicitOutputs: implicitOutputs, Input: srcFile, OrderOnly: deps, Args: map[string]string{ "cFlags": moduleCflags, "ccCmd": ccCmd, }, }) if tidy { tidyFile := android.ObjPathWithExt(ctx, subdir, srcFile, "tidy") tidyFiles = append(tidyFiles, tidyFile) ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: clangTidy, Output: tidyFile, Input: srcFile, // We must depend on objFile, since clang-tidy doesn't // support exporting dependencies. Implicit: objFile, Args: map[string]string{ "cFlags": moduleCflags, "tidyFlags": flags.tidyFlags, }, }) } if dump { sAbiDumpFile := android.ObjPathWithExt(ctx, subdir, srcFile, "sdump") sAbiDumpFiles = append(sAbiDumpFiles, sAbiDumpFile) ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: sAbiDump, Output: sAbiDumpFile, Input: srcFile, Implicit: objFile, Args: map[string]string{ "cFlags": moduleCflags, "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 := gccCmd(flags.toolchain, "ar") arFlags := "crsPD" if flags.arFlags != "" { arFlags += " " + flags.arFlags } ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: ar, 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, outputPath android.ModuleOutPath, deps android.Paths) { arFlags := "cqs" if len(objFiles) == 0 { dummy := android.PathForModuleOut(ctx, "dummy"+objectExtension) dummyAr := android.PathForModuleOut(ctx, "dummy"+staticLibraryExtension) ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: emptyFile, Output: dummy, Implicits: deps, }) ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: darwinAr, Output: dummyAr, Input: dummy, Args: map[string]string{ "arFlags": arFlags, }, }) ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: darwinAppendAr, Output: outputPath, 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.Strings(), 131072) if err != nil { ctx.ModuleErrorf("%s", err.Error()) } outputFile := outputPath.String() var in, out string for i, l := range objFilesLists { in = out out = outputFile if i != len(objFilesLists)-1 { out += "." + strconv.Itoa(i) } if in == "" { ctx.Build(pctx, blueprint.BuildParams{ Rule: darwinAr, Outputs: []string{out}, Inputs: l, Implicits: deps.Strings(), Args: map[string]string{ "arFlags": arFlags, }, }) } else { ctx.Build(pctx, blueprint.BuildParams{ Rule: darwinAppendAr, Outputs: []string{out}, Inputs: l, Args: map[string]string{ "arFlags": arFlags, "inAr": in, }, }) } } } // Generate a rule for compiling multiple .o files, plus static libraries, whole static libraries, // and shared libraires, 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) { var ldCmd string if flags.clang { ldCmd = "${config.ClangBin}/clang++" } else { ldCmd = gccCmd(flags.toolchain, "g++") } 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.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: ld, 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, symbolFile android.OptionalPath, apiLevel, baseName, exportedHeaderFlags string) android.OptionalPath { outputFile := android.PathForModuleOut(ctx, baseName+".lsdump") var symbolFileStr string var linkedDumpDep android.Path if symbolFile.Valid() { symbolFileStr = "-v " + symbolFile.Path().String() linkedDumpDep = symbolFile.Path() } ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: sAbiLink, Output: outputFile, Inputs: sAbiDumps, Implicit: linkedDumpDep, Args: map[string]string{ "symbolFile": symbolFileStr, "arch": ctx.Arch().ArchType.Name, "api": apiLevel, "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.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: unzipRefSAbiDump, Output: outputFile, Input: zippedRefDump, }) return outputFile } func SourceAbiDiff(ctx android.ModuleContext, inputDump android.Path, referenceDump android.Path, baseName string) android.OptionalPath { outputFile := android.PathForModuleOut(ctx, baseName+".abidiff") ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: sAbiDiff, Output: outputFile, Input: inputDump, Implicit: referenceDump, Args: map[string]string{ "referenceDump": referenceDump.String(), "libName": baseName, "arch": ctx.Arch().ArchType.Name, }, }) return android.OptionalPathForPath(outputFile) } // Generate a rule for extract a table of contents from a shared library (.so) func TransformSharedObjectToToc(ctx android.ModuleContext, inputFile android.WritablePath, outputFile android.WritablePath, flags builderFlags) { crossCompile := gccCmd(flags.toolchain, "") ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: toc, Output: outputFile, Input: inputFile, Args: map[string]string{ "crossCompile": crossCompile, }, }) } // 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) { var ldCmd string if flags.clang { ldCmd = "${config.ClangBin}/clang++" } else { ldCmd = gccCmd(flags.toolchain, "g++") } ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: partialLd, 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.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: prefixSymbols, 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" } ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: strip, Output: outputFile, Input: inputFile, Args: map[string]string{ "crossCompile": crossCompile, "args": args, }, }) } func TransformDarwinStrip(ctx android.ModuleContext, inputFile android.Path, outputFile android.WritablePath) { ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: darwinStrip, 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 CopyGccLib(ctx android.ModuleContext, libName string, flags builderFlags, outputFile android.WritablePath) { ctx.ModuleBuild(pctx, android.ModuleBuildParams{ Rule: copyGccLib, Output: outputFile, Args: map[string]string{ "ccCmd": gccCmd(flags.toolchain, "gcc"), "cFlags": flags.globalFlags, "libName": libName, }, }) } func gccCmd(toolchain config.Toolchain, cmd string) string { return filepath.Join(toolchain.GccRoot(), "bin", toolchain.GccTriple()+"-"+cmd) } func splitListForSize(list []string, limit int) (lists [][]string, err error) { var i int start := 0 bytes := 0 for i = range list { l := len(list[i]) 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 }