1 //===- ErrorHandler.h -------------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // We designed lld's error handlers with the following goals in mind:
10 //
11 //  - Errors can occur at any place where we handle user input, but we don't
12 //    want them to affect the normal execution path too much. Ideally,
13 //    handling errors should be as simple as reporting them and exit (but
14 //    without actually doing exit).
15 //
16 //    In particular, the design to wrap all functions that could fail with
17 //    ErrorOr<T> is rejected because otherwise we would have to wrap a large
18 //    number of functions in lld with ErrorOr. With that approach, if some
19 //    function F can fail, not only F but all functions that transitively call
20 //    F have to be wrapped with ErrorOr. That seemed too much.
21 //
22 //  - Finding only one error at a time is not sufficient. We want to find as
23 //    many errors as possible with one execution of the linker. That means the
24 //    linker needs to keep running after a first error and give up at some
25 //    checkpoint (beyond which it would find cascading, false errors caused by
26 //    the previous errors).
27 //
28 //  - We want a simple interface to report errors. Unlike Clang, the data we
29 //    handle is compiled binary, so we don't need an error reporting mechanism
30 //    that's as sophisticated as the one that Clang has.
31 //
32 // The current lld's error handling mechanism is simple:
33 //
34 //  - When you find an error, report it using error() and continue as far as
35 //    you can. An internal error counter is incremented by one every time you
36 //    call error().
37 //
38 //    A common idiom to handle an error is calling error() and then returning
39 //    a reasonable default value. For example, if your function handles a
40 //    user-supplied alignment value, and if you find an invalid alignment
41 //    (e.g. 17 which is not 2^n), you may report it using error() and continue
42 //    as if it were alignment 1 (which is the simplest reasonable value).
43 //
44 //    Note that you should not continue with an invalid value; that breaks the
45 //    internal consistency. You need to maintain all variables have some sane
46 //    value even after an error occurred. So, when you have to continue with
47 //    some value, always use a dummy value.
48 //
49 //  - Find a reasonable checkpoint at where you want to stop the linker, and
50 //    add code to return from the function if errorCount() > 0. In most cases,
51 //    a checkpoint already exists, so you don't need to do anything for this.
52 //
53 // This interface satisfies all the goals that we mentioned above.
54 //
55 // You should never call fatal() except for reporting a corrupted input file.
56 // fatal() immediately terminates the linker, so the function is not desirable
57 // if you are using lld as a subroutine in other program, and with that you
58 // can find only one error at a time.
59 //
60 // warn() doesn't do anything but printing out a given message.
61 //
62 // It is not recommended to use llvm::outs() or lld::errs() directly in lld
63 // because they are not thread-safe. The functions declared in this file are
64 // thread-safe.
65 //
66 //===----------------------------------------------------------------------===//
67 
68 #ifndef LLD_COMMON_ERRORHANDLER_H
69 #define LLD_COMMON_ERRORHANDLER_H
70 
71 #include "lld/Common/LLVM.h"
72 
73 #include "llvm/ADT/STLExtras.h"
74 #include "llvm/Support/Error.h"
75 #include "llvm/Support/FileOutputBuffer.h"
76 
77 namespace llvm {
78 class DiagnosticInfo;
79 class raw_ostream;
80 }
81 
82 namespace lld {
83 
84 // We wrap stdout and stderr so that you can pass alternative stdout/stderr as
85 // arguments to lld::*::link() functions.
86 extern llvm::raw_ostream *stdoutOS;
87 extern llvm::raw_ostream *stderrOS;
88 
89 llvm::raw_ostream &outs();
90 llvm::raw_ostream &errs();
91 
92 class ErrorHandler {
93 public:
94   uint64_t errorCount = 0;
95   uint64_t errorLimit = 20;
96   StringRef errorLimitExceededMsg = "too many errors emitted, stopping now";
97   StringRef logName = "lld";
98   bool exitEarly = true;
99   bool fatalWarnings = false;
100   bool verbose = false;
101   bool vsDiagnostics = false;
102 
103   void error(const Twine &msg);
104   LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &msg);
105   void log(const Twine &msg);
106   void message(const Twine &msg);
107   void warn(const Twine &msg);
108 
109   std::unique_ptr<llvm::FileOutputBuffer> outputBuffer;
110 
111 private:
112   using Colors = raw_ostream::Colors;
113 
114   std::string getLocation(const Twine &msg);
115 };
116 
117 /// Returns the default error handler.
118 ErrorHandler &errorHandler();
119 
120 inline void error(const Twine &msg) { errorHandler().error(msg); }
121 inline LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &msg) {
122   errorHandler().fatal(msg);
123 }
124 inline void log(const Twine &msg) { errorHandler().log(msg); }
125 inline void message(const Twine &msg) { errorHandler().message(msg); }
126 inline void warn(const Twine &msg) { errorHandler().warn(msg); }
127 inline uint64_t errorCount() { return errorHandler().errorCount; }
128 
129 LLVM_ATTRIBUTE_NORETURN void exitLld(int val);
130 
131 void diagnosticHandler(const llvm::DiagnosticInfo &di);
132 void checkError(Error e);
133 
134 // check functions are convenient functions to strip errors
135 // from error-or-value objects.
136 template <class T> T check(ErrorOr<T> e) {
137   if (auto ec = e.getError())
138     fatal(ec.message());
139   return std::move(*e);
140 }
141 
142 template <class T> T check(Expected<T> e) {
143   if (!e)
144     fatal(llvm::toString(e.takeError()));
145   return std::move(*e);
146 }
147 
148 template <class T>
149 T check2(ErrorOr<T> e, llvm::function_ref<std::string()> prefix) {
150   if (auto ec = e.getError())
151     fatal(prefix() + ": " + ec.message());
152   return std::move(*e);
153 }
154 
155 template <class T>
156 T check2(Expected<T> e, llvm::function_ref<std::string()> prefix) {
157   if (!e)
158     fatal(prefix() + ": " + toString(e.takeError()));
159   return std::move(*e);
160 }
161 
162 inline std::string toString(const Twine &s) { return s.str(); }
163 
164 // To evaluate the second argument lazily, we use C macro.
165 #define CHECK(E, S) check2((E), [&] { return toString(S); })
166 
167 } // namespace lld
168 
169 #endif
170