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//===- ErrorHandler.h -------------------------------------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// We designed lld's error handlers with the following goals in mind:
// - Errors can occur at any place where we handle user input, but we don't
// want them to affect the normal execution path too much. Ideally,
// handling errors should be as simple as reporting them and exit (but
// without actually doing exit).
// In particular, the design to wrap all functions that could fail with
// ErrorOr<T> is rejected because otherwise we would have to wrap a large
// number of functions in lld with ErrorOr. With that approach, if some
// function F can fail, not only F but all functions that transitively call
// F have to be wrapped with ErrorOr. That seemed too much.
// - Finding only one error at a time is not sufficient. We want to find as
// many errors as possible with one execution of the linker. That means the
// linker needs to keep running after a first error and give up at some
// checkpoint (beyond which it would find cascading, false errors caused by
// the previous errors).
// - We want a simple interface to report errors. Unlike Clang, the data we
// handle is compiled binary, so we don't need an error reporting mechanism
// that's as sophisticated as the one that Clang has.
// The current lld's error handling mechanism is simple:
// - When you find an error, report it using error() and continue as far as
// you can. An internal error counter is incremented by one every time you
// call error().
// A common idiom to handle an error is calling error() and then returning
// a reasonable default value. For example, if your function handles a
// user-supplied alignment value, and if you find an invalid alignment
// (e.g. 17 which is not 2^n), you may report it using error() and continue
// as if it were alignment 1 (which is the simplest reasonable value).
// Note that you should not continue with an invalid value; that breaks the
// internal consistency. You need to maintain all variables have some sane
// value even after an error occurred. So, when you have to continue with
// some value, always use a dummy value.
// - Find a reasonable checkpoint at where you want to stop the linker, and
// add code to return from the function if errorCount() > 0. In most cases,
// a checkpoint already exists, so you don't need to do anything for this.
// This interface satisfies all the goals that we mentioned above.
// You should never call fatal() except for reporting a corrupted input file.
// fatal() immediately terminates the linker, so the function is not desirable
// if you are using lld as a subroutine in other program, and with that you
// can find only one error at a time.
// warn() doesn't do anything but printing out a given message.
// It is not recommended to use llvm::outs() or lld::errs() directly in lld
// because they are not thread-safe. The functions declared in this file are
// thread-safe.
#include "lld/Common/LLVM.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/FileOutputBuffer.h"
namespace llvm {
class DiagnosticInfo;
class raw_ostream;
namespace lld {
// We wrap stdout and stderr so that you can pass alternative stdout/stderr as
// arguments to lld::*::link() functions.
extern llvm::raw_ostream *stdoutOS;
extern llvm::raw_ostream *stderrOS;
llvm::raw_ostream &outs();
llvm::raw_ostream &errs();
enum class ErrorTag { LibNotFound, SymbolNotFound };
class ErrorHandler {
uint64_t errorCount = 0;
uint64_t errorLimit = 20;
StringRef errorLimitExceededMsg = "too many errors emitted, stopping now";
StringRef errorHandlingScript;
StringRef logName = "lld";
bool exitEarly = true;
bool fatalWarnings = false;
bool verbose = false;
bool vsDiagnostics = false;
bool disableOutput = false;
std::function<void()> cleanupCallback;
void error(const Twine &msg);
void error(const Twine &msg, ErrorTag tag, ArrayRef<StringRef> args);
[[noreturn]] void fatal(const Twine &msg);
void log(const Twine &msg);
void message(const Twine &msg, llvm::raw_ostream &s);
void warn(const Twine &msg);
void reset() {
if (cleanupCallback)
*this = ErrorHandler();
std::unique_ptr<llvm::FileOutputBuffer> outputBuffer;
using Colors = raw_ostream::Colors;
std::string getLocation(const Twine &msg);
void reportDiagnostic(StringRef location, Colors c, StringRef diagKind,
const Twine &msg);
/// Returns the default error handler.
ErrorHandler &errorHandler();
inline void error(const Twine &msg) { errorHandler().error(msg); }
inline void error(const Twine &msg, ErrorTag tag, ArrayRef<StringRef> args) {
errorHandler().error(msg, tag, args);
[[noreturn]] inline void fatal(const Twine &msg) { errorHandler().fatal(msg); }
inline void log(const Twine &msg) { errorHandler().log(msg); }
inline void message(const Twine &msg, llvm::raw_ostream &s = outs()) {
errorHandler().message(msg, s);
inline void warn(const Twine &msg) { errorHandler().warn(msg); }
inline uint64_t errorCount() { return errorHandler().errorCount; }
[[noreturn]] void exitLld(int val);
void diagnosticHandler(const llvm::DiagnosticInfo &di);
void checkError(Error e);
// check functions are convenient functions to strip errors
// from error-or-value objects.
template <class T> T check(ErrorOr<T> e) {
if (auto ec = e.getError())
return std::move(*e);
template <class T> T check(Expected<T> e) {
if (!e)
return std::move(*e);
// Don't move from Expected wrappers around references.
template <class T> T &check(Expected<T &> e) {
if (!e)
return *e;
template <class T>
T check2(ErrorOr<T> e, llvm::function_ref<std::string()> prefix) {
if (auto ec = e.getError())
fatal(prefix() + ": " + ec.message());
return std::move(*e);
template <class T>
T check2(Expected<T> e, llvm::function_ref<std::string()> prefix) {
if (!e)
fatal(prefix() + ": " + toString(e.takeError()));
return std::move(*e);
inline std::string toString(const Twine &s) { return s.str(); }
// To evaluate the second argument lazily, we use C macro.
#define CHECK(E, S) check2((E), [&] { return toString(S); })
} // namespace lld