[ELF] Add context-aware diagnostic functions (#112319)

The current diagnostic functions log/warn/error/fatal lack a context
argument and call the global `lld::errorHandler()`, which prevents
multiple lld instances in one process.

This patch introduces context-aware replacements:

* log => Log(ctx)
* warn => Warn(ctx)
* errorOrWarn => Err(ctx)
* error => ErrAlways(ctx)
* fatal => Fatal(ctx)

Example: `errorOrWarn(toString(f) + "xxx")` => `Err(ctx) << f << "xxx"`.
(`toString(f)` is shortened to `f` as a bonus and may access `ctx`
without accessing the global variable (see `Target.cpp`)).

`ctx.e = &context->e;` can be replaced with a non-global Errorhandler
when `ctx` becomes a local variable.

(For the ELF port, the long term goal is to eliminate `error`. Most can
be straightforwardly converted to `Err(ctx)`.)

lld/Common/ErrorHandler.cpp

@@ -335,3 +335,21 @@ void ErrorHandler::fatal(const Twine &msg) {
   error(msg);
   exitLld(1);
 }
+
+SyncStream::~SyncStream() {
+  os.flush();
+  switch (level) {
+  case DiagLevel::Log:
+    e.log(buf);
+    break;
+  case DiagLevel::Warn:
+    e.warn(buf);
+    break;
+  case DiagLevel::Err:
+    e.error(buf);
+    break;
+  case DiagLevel::Fatal:
+    e.fatal(buf);
+    break;
+  }
+}

lld/ELF/Config.h

@@ -547,6 +547,8 @@ struct Ctx {
   LinkerScript *script;
   std::unique_ptr<TargetInfo> target;
 
+  ErrorHandler *errHandler;
+
   // These variables are initialized by Writer and should not be used before
   // Writer is initialized.
   uint8_t *bufferStart;
@@ -679,6 +681,39 @@ static inline void internalLinkerError(StringRef loc, const Twine &msg) {
               llvm::getBugReportMsg());
 }
 
+struct ELFSyncStream : SyncStream {
+  Ctx &ctx;
+  ELFSyncStream(Ctx &ctx, DiagLevel level)
+      : SyncStream(*ctx.errHandler, level), ctx(ctx) {}
+};
+
+template <typename T>
+std::enable_if_t<!std::is_pointer_v<std::remove_reference_t<T>>,
+                 const ELFSyncStream &>
+operator<<(const ELFSyncStream &s, T &&v) {
+  s.os << std::forward<T>(v);
+  return s;
+}
+
+// Report a log if --verbose is specified.
+ELFSyncStream Log(Ctx &ctx);
+
+// Report a warning. Upgraded to an error if --fatal-warnings is specified.
+ELFSyncStream Warn(Ctx &ctx);
+
+// Report an error that will suppress the output file generation. Downgraded to
+// a warning if --noinhibit-exec is specified.
+ELFSyncStream Err(Ctx &ctx);
+
+// Report an error regardless of --noinhibit-exec.
+ELFSyncStream ErrAlways(Ctx &ctx);
+
+// Report a fatal error that exits immediately. This should generally be avoided
+// in favor of Err.
+ELFSyncStream Fatal(Ctx &ctx);
+
+uint64_t errCount(Ctx &ctx);
+
 } // namespace lld::elf
 
 #endif

lld/ELF/Driver.cpp

@@ -91,6 +91,15 @@ void elf::errorOrWarn(const Twine &msg) {
     error(msg);
 }
 
+ELFSyncStream elf::Log(Ctx &ctx) { return {ctx, DiagLevel::Log}; }
+ELFSyncStream elf::Warn(Ctx &ctx) { return {ctx, DiagLevel::Warn}; }
+ELFSyncStream elf::Err(Ctx &ctx) {
+  return {ctx, ctx.arg.noinhibitExec ? DiagLevel::Warn : DiagLevel::Err};
+}
+ELFSyncStream elf::ErrAlways(Ctx &ctx) { return {ctx, DiagLevel::Err}; }
+ELFSyncStream elf::Fatal(Ctx &ctx) { return {ctx, DiagLevel::Fatal}; }
+uint64_t elf::errCount(Ctx &ctx) { return ctx.errHandler->errorCount; }
+
 Ctx::Ctx() : driver(*this) {}
 
 void Ctx::reset() {
@@ -101,6 +110,8 @@ void Ctx::reset() {
   script = nullptr;
   target.reset();
 
+  errHandler = nullptr;
+
   bufferStart = nullptr;
   mainPart = nullptr;
   tlsPhdr = nullptr;
@@ -169,6 +180,7 @@ bool link(ArrayRef<const char *> args, llvm::raw_ostream &stdoutOS,
   Ctx &ctx = elf::ctx;
   LinkerScript script(ctx);
   ctx.script = &script;
+  ctx.errHandler = &context->e;
   ctx.symAux.emplace_back();
   ctx.symtab = std::make_unique<SymbolTable>(ctx);
 
@@ -179,7 +191,7 @@ bool link(ArrayRef<const char *> args, llvm::raw_ostream &stdoutOS,
 
   ctx.driver.linkerMain(args);
 
-  return errorCount() == 0;
+  return errCount(ctx) == 0;
 }
 } // namespace elf
 } // namespace lld
@@ -366,7 +378,7 @@ void LinkerDriver::addFile(StringRef path, bool withLOption) {
       files.push_back(createObjFile(ctx, mbref, "", inLib));
     break;
   default:
-    error(path + ": unknown file type");
+    ErrAlways(ctx) << path << ": unknown file type";
   }
 }
 
@@ -2780,8 +2792,9 @@ static void readSecurityNotes(Ctx &ctx) {
     if (ctx.arg.zForceBti && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
       features |= GNU_PROPERTY_AARCH64_FEATURE_1_BTI;
       if (ctx.arg.zBtiReport == "none")
-        warn(toString(f) + ": -z force-bti: file does not have "
-                           "GNU_PROPERTY_AARCH64_FEATURE_1_BTI property");
+        Warn(ctx) << f
+                  << ": -z force-bti: file does not have "
+                     "GNU_PROPERTY_AARCH64_FEATURE_1_BTI property";
     } else if (ctx.arg.zForceIbt &&
                !(features & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
       if (ctx.arg.zCetReport == "none")
@@ -3048,7 +3061,7 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
       oldFilenames.insert(f->getName());
     for (InputFile *newFile : newInputFiles)
       if (!oldFilenames.contains(newFile->getName()))
-        errorOrWarn("input file '" + newFile->getName() + "' added after LTO");
+        Err(ctx) << "input file '" << newFile->getName() << "' added after LTO";
   }
 
   // Handle --exclude-libs again because lto.tmp may reference additional

lld/ELF/InputFiles.cpp

@@ -66,6 +66,12 @@ std::string lld::toString(const InputFile *f) {
   return std::string(f->toStringCache);
 }
 
+const ELFSyncStream &elf::operator<<(const ELFSyncStream &s,
+                                     const InputFile *f) {
+  s << toString(f);
+  return s;
+}
+
 static ELFKind getELFKind(MemoryBufferRef mb, StringRef archiveName) {
   unsigned char size;
   unsigned char endian;

lld/ELF/InputFiles.h

@@ -386,6 +386,8 @@ ELFFileBase *createObjFile(Ctx &, MemoryBufferRef mb,
 
 std::string replaceThinLTOSuffix(Ctx &, StringRef path);
 
+const ELFSyncStream &operator<<(const ELFSyncStream &, const InputFile *);
+
 } // namespace elf
 } // namespace lld
 

lld/ELF/Target.cpp

@@ -45,6 +45,15 @@ std::string lld::toString(RelType type) {
   return std::string(s);
 }
 
+const ELFSyncStream &elf::operator<<(const ELFSyncStream &s, RelType type) {
+  StringRef buf = getELFRelocationTypeName(s.ctx.arg.emachine, type);
+  if (buf == "Unknown")
+    s << "Unknown (" << type << ')';
+  else
+    s << buf;
+  return s;
+}
+
 void elf::setTarget(Ctx &ctx) {
   switch (ctx.arg.emachine) {
   case EM_386:

lld/ELF/Target.h

@@ -327,6 +327,8 @@ inline uint64_t overwriteULEB128(uint8_t *bufLoc, uint64_t val) {
   *bufLoc = val;
   return val;
 }
+
+const ELFSyncStream &operator<<(const ELFSyncStream &, RelType);
 } // namespace elf
 } // namespace lld
 

lld/include/lld/Common/ErrorHandler.h

@@ -73,11 +73,11 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/raw_ostream.h"
 #include <mutex>
 
 namespace llvm {
 class DiagnosticInfo;
-class raw_ostream;
 }
 
 namespace lld {
@@ -152,6 +152,21 @@ void message(const Twine &msg, llvm::raw_ostream &s = outs());
 void warn(const Twine &msg);
 uint64_t errorCount();
 
+enum class DiagLevel { Log, Warn, Err, Fatal };
+
+// A class that synchronizes thread writing to the same stream similar
+// std::osyncstream.
+class SyncStream {
+  ErrorHandler &e;
+  DiagLevel level;
+  std::string buf;
+
+public:
+  mutable llvm::raw_string_ostream os{buf};
+  SyncStream(ErrorHandler &e, DiagLevel level) : e(e), level(level) {}
+  ~SyncStream();
+};
+
 [[noreturn]] void exitLld(int val);
 
 void diagnosticHandler(const llvm::DiagnosticInfo &di);