clang不止是前端編譯器，更是連接了LLVM整個(gè)編譯過程和其他工具的一個(gè)驅(qū)動(dòng)程序性宏。
在 clang/include/clang/Basic 目錄下定義了眾多td模版文件滥壕，例如DiagnosticDriverKinds.td就是Driver的相關(guān)診斷信息丑婿。對(duì)應(yīng)的類型則是在 clang/include/clang/Basic/DiagnosticIDs.h 文件中定義了6個(gè)類型：
/// Used for handling and querying diagnostic IDs.
///
/// Can be used and shared by multiple Diagnostics for multiple translation units.
class DiagnosticIDs : public RefCountedBase<DiagnosticIDs> {
public:
/// The level of the diagnostic, after it has been through mapping.
enum Level {
Ignored, Note, Remark, Warning, Error, Fatal
};
clang driver
clang Driver 負(fù)責(zé)拼接編譯器命令和 ld 命令。
他的處理原理如下：
- Parse：解析傳入的參數(shù)
- Pipeline：根據(jù)每個(gè)輸入的文件和類型留拾，組建action，具體類型可以查看ActionClass枚舉類型鲫尊，對(duì)應(yīng)到具體的JobAction
- Bind：根據(jù)action選擇對(duì)應(yīng)的工具和文件名信息痴柔，具體可以通過
clang -ccc-print-bindings進(jìn)行查看 - Translate：將輸入的參數(shù)轉(zhuǎn)換為不同的tool的參數(shù)。如clang -cc1 -arch arm64疫向，在clang中使用的是-triple arm64-apple-ios14竞帽，而ld則會(huì)使用-arch arm64
- Execute：調(diào)用tool執(zhí)行任務(wù)。該步驟會(huì)通過創(chuàng)建子進(jìn)程方式調(diào)用tool鸿捧。
舉個(gè)實(shí)例：
/Test ? xcrun -l clang test.c -v -O2 -o Test n14637@GIH-D-21687
env SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang test.c -v -O2 -o Test
Apple clang version 12.0.0 (clang-1200.0.32.29)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.15.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mframe-pointer=all -fno-strict-return -masm-verbose -munwind-tables -target-sdk-version=10.15.6 -fcompatibility-qualified-id-block-type-checking -target-cpu penryn -dwarf-column-info -debugger-tuning=lldb -target-linker-version 609.8 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -I/usr/local/include -internal-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/local/include -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/include -internal-externc-isystem /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include -O2 -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -fdebug-compilation-dir /Test -ferror-limit 19 -fmessage-length 164 -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fobjc-runtime=macosx-10.15.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o /var/folders/71/830m4bcj2_v1ly5qbtsbhxm4w50c2h/T/test-72900e.o -x c test.c
clang -cc1 version 12.0.0 (clang-1200.0.32.29) default target x86_64-apple-darwin19.6.0
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/local/include"
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/include
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -dynamic -arch x86_64 -platform_version macos 10.15.0 10.15.6 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk -o Test -L/usr/local/lib /var/folders/71/830m4bcj2_v1ly5qbtsbhxm4w50c2h/T/test-72900e.o -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/lib/darwin/libclang_rt.osx.a
可以看到屹篓，執(zhí)行xcrun之后，實(shí)際上clang構(gòu)造了兩個(gè)job匙奴，一個(gè)是編譯任務(wù)堆巧，一個(gè)是鏈接任務(wù)，最后根據(jù)job創(chuàng)建兩個(gè)進(jìn)程執(zhí)行任務(wù)。
看到源碼部分谍肤，在driver.cpp：
//解析參數(shù)啦租，該方法會(huì)調(diào)用DriverOptTable中的getDriverOptTable方法判斷clang driver支持的所有參數(shù)類型
//其內(nèi)部的OptTable::Info InfoTable[]是通過clang/Driver/Options.inc生成的，而inc是由tablegen將optins.td轉(zhuǎn)換的
IntrusiveRefCntPtr<DiagnosticOptions> DiagOpts =
CreateAndPopulateDiagOpts(argv);
//診斷引擎綁定到一個(gè)翻譯單元和一個(gè)SourceManager荒揣。
DiagnosticsEngine Diags(DiagID, &*DiagOpts, DiagClient);
//并將diagnostics傳遞給DiagnosticConsumer篷角，以便向用戶報(bào)告
if (!DiagOpts->DiagnosticSerializationFile.empty()) {
auto SerializedConsumer =
clang::serialized_diags::create(DiagOpts->DiagnosticSerializationFile,
&*DiagOpts, /*MergeChildRecords=*/true);
Diags.setClient(new ChainedDiagnosticConsumer(
Diags.takeClient(), std::move(SerializedConsumer)));
}
ProcessWarningOptions(Diags, *DiagOpts, /*ReportDiags=*/false);
//創(chuàng)建driver實(shí)例
Driver TheDriver(Path, llvm::sys::getDefaultTargetTriple(), Diags);
SetInstallDir(argv, TheDriver, CanonicalPrefixes);
TheDriver.setTargetAndMode(TargetAndMode);
//xxx
//1.構(gòu)造需要執(zhí)行的命令，跳轉(zhuǎn)到最下面的方法??
std::unique_ptr<Compilation> C(TheDriver.BuildCompilation(argv));
//2.構(gòu)建action
if (TC.getTriple().isOSBinFormatMachO())
BuildUniversalActions(*C, C->getDefaultToolChain(), Inputs);
else
BuildActions(*C, C->getArgs(), Inputs, C->getActions());
//3.構(gòu)建jobs
BuildJobs(*C);
//4.執(zhí)行任務(wù)
Driver::ExecuteCompilation -> Compilation::ExecuteJobs -> Compilation::ExecuteCommand-> Command::Execute -> llvm::sys::ExecuteAndWait
Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
//xxx
//1.1.根據(jù)命令行指定的參數(shù)進(jìn)行解析
CLOptions = std::make_unique<InputArgList>(
ParseArgStrings(ArgList.slice(1), IsCLMode(), ContainsError));
//1.2.獲取triple并通過gettoolchain獲取對(duì)應(yīng)的toolchain
const ToolChain &TC = getToolChain(
*UArgs, computeTargetTriple(*this, TargetTriple, *UArgs));
//1.3.Compilation類接管參數(shù)
Compilation *C = new Compilation(*this, TC, UArgs.release(), TranslatedArgs,
ContainsError);
//1.4.獲取輸入文件進(jìn)行編譯系任，該方法會(huì)通過輸入的文件擴(kuò)展后綴獲取文件類型
BuildInputs(C->getDefaultToolChain(), *TranslatedArgs, Inputs);
}
//1.1.1.
InputArgList Driver::ParseArgStrings(ArrayRef<const char *> ArgStrings,
bool IsClCompatMode,
bool &ContainsError) {
//調(diào)用getOpts獲取支持的所有參數(shù)恳蹲，然后調(diào)用parseArgs對(duì)命令行參數(shù)進(jìn)行解析
//解析的規(guī)則則是通過調(diào)用OptTable的ParseOneArg方法對(duì)字符串進(jìn)行遍歷解析
//ParseOneArg內(nèi)部調(diào)用了accept方法，該方法對(duì)參數(shù)別名會(huì)進(jìn)行判斷和特殊處理俩滥，如下:
InputArgList Args =
getOpts().ParseArgs(ArgStrings, MissingArgIndex, MissingArgCount,
IncludedFlagsBitmask, ExcludedFlagsBitmask);
//判斷參數(shù)是否支持嘉蕾，是否支持通過Optins.td文件進(jìn)行查找，否則拋出異常
for (const Arg *A : Args) {
if (A->getOption().hasFlag(options::Unsupported)) {
DiagID = diag::err_drv_unsupported_opt;
Diag(DiagID) << ArgString;
}
}
Arg *Option::accept(const ArgList &Args,
unsigned &Index,
unsigned ArgSize) const {
//解析參數(shù)
std::unique_ptr<Arg> A(acceptInternal(Args, Index, ArgSize));
if (!A)
return nullptr;
//判斷是否有別名
const Option &UnaliasedOption = getUnaliasedOption();
if (getID() == UnaliasedOption.getID())
return A.release();
//從unalias選項(xiàng)中獲取拼寫霜旧，對(duì)應(yīng)的關(guān)系在Optins.td中有聲明
StringRef UnaliasedSpelling = Args.MakeArgString(
Twine(UnaliasedOption.getPrefix()) + Twine(UnaliasedOption.getName()));
}
void Driver::BuildUniversalActions(Compilation &C, const ToolChain &TC,
const InputList &BAInputs) const {
//2.1.根據(jù)-arch參數(shù)生成需要處理的的Archs错忱，構(gòu)建actions
DerivedArgList &Args = C.getArgs();
ActionList &Actions = C.getActions();
for (Arg *A : Args) {
if (A->getOption().matches(options::OPT_arch)) {
//xxx
if (ArchNames.insert(A->getValue()).second)
Archs.push_back(A->getValue());
}
}
//如果沒有傳入 -arch 參數(shù)，則獲取 triple 對(duì)應(yīng)的架構(gòu)
if (!Archs.size())
Archs.push_back(Args.MakeArgString(TC.getDefaultUniversalArchName()));
ActionList SingleActions;
//調(diào)用 Driver::handleArguments 方法對(duì)參數(shù)進(jìn)行處理
BuildActions(C, Args, BAInputs, SingleActions);
// 構(gòu)建 offloading actions.
OffloadingActionBuilder OffloadBuilder(C, Args, Inputs);
// 構(gòu)造要執(zhí)行的actions
HeaderModulePrecompileJobAction *HeaderModuleAction = nullptr;
ActionList LinkerInputs;
ActionList MergerInputs;
for (auto &I : Inputs) {
types::ID InputType = I.first;
const Arg *InputArg = I.second;
//根據(jù)輸入源碼文件inputs獲取需要處理的 phase 數(shù)組
//phase其實(shí)就是一個(gè)枚舉類型挂据，包含Preprocess Precompile Compile Backend Assemble Link IfsMerge
//在 Types.def 文件維護(hù)了不同文件類型默認(rèn)情況下需要經(jīng)歷的 phase
llvm::SmallVector<phases::ID, phases::MaxNumberOfPhases> PL;
types::getCompilationPhases(*this, Args, InputType, PL);
if (PL.empty())
continue;
//xxx
}
//2.2.
void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
const InputList &Inputs, ActionList &Actions) const {
//將每個(gè)phase轉(zhuǎn)化為一個(gè)action
for (phases::ID Phase : PL) {
//xxx
// Otherwise construct the appropriate action.
//該方法內(nèi)部根據(jù)Phase的類型進(jìn)行action的構(gòu)建以清，詳情在個(gè)下方法：
Action *NewCurrent = ConstructPhaseAction(C, Args, Phase, Current);
if (auto *HMA = dyn_cast<HeaderModulePrecompileJobAction>(NewCurrent))
HeaderModuleAction = HMA;
Current = NewCurrent;
// Use the current host action in any of the offloading actions, if
// required.
if (OffloadBuilder.addHostDependenceToDeviceActions(Current, InputArg))
break;
if (Current->getType() == types::TY_Nothing)
break;
}
}
Action *Driver::ConstructPhaseAction(
Compilation &C, const ArgList &Args, phases::ID Phase, Action *Input,
Action::OffloadKind TargetDeviceOffloadKind) const {
switch (Phase) {
case phases::Preprocess: {
//通過 Input 和 OutputTy 構(gòu)建 PreprocessJobAction
return C.MakeAction<PreprocessJobAction>(Input, OutputTy);
}
return C.MakeAction<PrecompileJobAction>(Input, OutputTy);
}
case phases::Compile: {
return C.MakeAction<CompileJobAction>(Input, types::TY_LLVM_BC);
}
case phases::Backend: {
if (isUsingLTO() && TargetDeviceOffloadKind == Action::OFK_None) {
types::ID Output =
Args.hasArg(options::OPT_S) ? types::TY_LTO_IR : types::TY_LTO_BC;
return C.MakeAction<BackendJobAction>(Input, Output);
}
if (Args.hasArg(options::OPT_emit_llvm)) {
types::ID Output =
Args.hasArg(options::OPT_S) ? types::TY_LLVM_IR : types::TY_LLVM_BC;
return C.MakeAction<BackendJobAction>(Input, Output);
}
return C.MakeAction<BackendJobAction>(Input, types::TY_PP_Asm);
}
case phases::Assemble:
return C.MakeAction<AssembleJobAction>(std::move(Input), types::TY_Object);
}
}
//3.構(gòu)建jobs
void Driver::BuildJobs(Compilation &C) const {
//1.收集需要處理的架構(gòu)
llvm::StringSet<> ArchNames;
if (C.getDefaultToolChain().getTriple().isOSBinFormatMachO())
for (const Arg *A : C.getArgs())
if (A->getOption().matches(options::OPT_arch))
ArchNames.insert(A->getValue());
//2.緩存action和inputinfo的映射
//BuildJobsForAction 方法會(huì)先查找緩存，如果緩存中不存在則再調(diào)用 BuildJobsForActionNoCache 方法創(chuàng)建 InputInfo
std::map<std::pair<const Action *, std::string>, InputInfo> CachedResults;
BuildJobsForAction(C, A, &C.getDefaultToolChain(),
/*BoundArch*/ StringRef(),
/*AtTopLevel*/ true,
/*MultipleArchs*/ ArchNames.size() > 1,
/*LinkingOutput*/ LinkingOutput, CachedResults,
/*TargetDeviceOffloadKind*/ Action::OFK_None);
}
InputInfo Driver::BuildJobsForActionNoCache(
Compilation &C, const Action *A, const ToolChain *TC, StringRef BoundArch,
bool AtTopLevel, bool MultipleArchs, const char *LinkingOutput,
std::map<std::pair<const Action *, std::string>, InputInfo> &CachedResults,
Action::OffloadKind TargetDeviceOffloadKind) const {
if (const BindArchAction *BAA = dyn_cast<BindArchAction>(A)) {
const ToolChain *TC;
StringRef ArchName = BAA->getArchName();
//3.通過 computeTargetTriple 計(jì)算 triple崎逃，然后獲取合適的工具鏈
// computeTargetTriple會(huì)獲取-target參數(shù)更新TargetTriple字符串玖媚，然后根據(jù)其生產(chǎn)Triple實(shí)例
if (!ArchName.empty())
TC = &getToolChain(C.getArgs(),
computeTargetTriple(*this, TargetTriple,
C.getArgs(), ArchName));
else
TC = &C.getDefaultToolChain();
//4.隨后會(huì)以 BindArchAction 持有的第一個(gè) input（類型是 LinkJobAction）為參數(shù)再次調(diào)用 BuildJobsForAction 方法
return BuildJobsForAction(C, *BAA->input_begin(), TC, ArchName, AtTopLevel,
MultipleArchs, LinkingOutput, CachedResults,
TargetDeviceOffloadKind);
}
//5.獲取 LinkJobAction 的 Inputs
ActionList Inputs = A->getInputs();
const JobAction *JA = cast<JobAction>(A);
ActionList CollapsedOffloadActions;
//6.創(chuàng)建 ToolSelector 的實(shí)例 TS，并調(diào)用 ToolSelector::getTool 獲取支持 link 的工具
ToolSelector TS(JA, *TC, C, isSaveTempsEnabled(),
embedBitcodeInObject() && !isUsingLTO());
const Tool *T = TS.getTool(Inputs, CollapsedOffloadActions);
//7.通過 BuildJobsForAction 處理 Inputs
for (const auto *OA : CollapsedOffloadActions)
cast<OffloadAction>(OA)->doOnEachDependence(
/*IsHostDependence=*/BuildingForOffloadDevice,
[&](Action *DepA, const ToolChain *DepTC, const char *DepBoundArch) {
OffloadDependencesInputInfo.push_back(BuildJobsForAction(
C, DepA, DepTC, DepBoundArch, /* AtTopLevel */ false,
/*MultipleArchs=*/!!DepBoundArch, LinkingOutput, CachedResults,
DepA->getOffloadingDeviceKind()));
});
//xxx
//調(diào)用 Compilation::getArgsForToolChain 進(jìn)行參數(shù)轉(zhuǎn)換
llvm::Triple EffectiveTriple;
const ToolChain &ToolTC = T->getToolChain();
const ArgList &Args =
C.getArgsForToolChain(TC, BoundArch, A->getOffloadingDeviceKind());
//xxx
if (UnbundlingResults.empty())
//調(diào)用 darwin::Linker 的 ConstructJob 方法構(gòu)建 Job
T->ConstructJob(
C, *JA, Result, InputInfos,
C.getArgsForToolChain(TC, BoundArch, JA->getOffloadingDeviceKind()),
LinkingOutput);
else
T->ConstructJobMultipleOutputs(
C, *JA, UnbundlingResults, InputInfos,
C.getArgsForToolChain(TC, BoundArch, JA->getOffloadingDeviceKind()),
LinkingOutput);
}
