[llvm-readobj] Prepend argv[0] to error/warning messages

Summary:
Currently, we report:

    error: ...

Prepend argv[0] (tool name):

    llvm-readobj: error: ...

This is consistent with most GNU binutils/clang/lld, and gives a bit
more context in a long build log.

Reviewed By: grimar, jhenderson, rupprecht

Differential Revision: https://reviews.llvm.org/D66425

llvm-svn: 369377

llvm/test/tools/llvm-readobj/error-format.test

@@ -0,0 +1,19 @@
+## This test shows that we include the tool name in error/warning messages.
+
+# RUN: not llvm-readelf %S/non-existent 2>&1 | FileCheck --check-prefix=ERR %s -DTOOL=readelf
+# RUN: not llvm-readobj %S/non-existent 2>&1 | FileCheck --check-prefix=ERR %s -DTOOL=readobj
+
+# ERR: llvm-[[TOOL]]{{(\.exe)?}}: error: '{{.*}}': {{[Nn]}}o such file or directory
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readelf -x 10 %t 2>&1 | FileCheck --check-prefix=WARN %s -DTOOL=readelf
+# RUN: llvm-readobj -x 10 %t 2>&1 | FileCheck --check-prefix=WARN %s -DTOOL=readobj
+
+# WARN: llvm-[[TOOL]]{{(\.exe)?}}: warning: '{{.*}}': could not find section 10
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_RISCV

llvm/tools/llvm-readobj/llvm-readobj.cpp

@@ -373,6 +373,8 @@ namespace opts {
       HelpResponse("\nPass @FILE as argument to read options from FILE.\n");
 } // namespace opts
 
+static StringRef ToolName;
+
 namespace llvm {
 
 LLVM_ATTRIBUTE_NORETURN static void error(Twine Msg) {
@@ -380,7 +382,7 @@ LLVM_ATTRIBUTE_NORETURN static void error(Twine Msg) {
   // proper place.
   fouts().flush();
   errs() << "\n";
-  WithColor::error(errs()) << Msg << "\n";
+  WithColor::error(errs(), ToolName) << Msg << "\n";
   exit(1);
 }
 
@@ -401,11 +403,11 @@ void reportWarning(Error Err, StringRef Input) {
   // Flush the standard output to print the warning at a
   // proper place.
   fouts().flush();
-  handleAllErrors(createFileError(Input, std::move(Err)),
-                  [&](const ErrorInfoBase &EI) {
-                    errs() << "\n";
-                    WithColor::warning(errs()) << EI.message() << "\n";
-                  });
+  handleAllErrors(
+      createFileError(Input, std::move(Err)), [&](const ErrorInfoBase &EI) {
+        errs() << "\n";
+        WithColor::warning(errs(), ToolName) << EI.message() << "\n";
+      });
 }
 
 LLVM_ATTRIBUTE_NORETURN void reportError(std::error_code EC, StringRef Input) {
@@ -703,6 +705,7 @@ static void registerReadelfAliases() {
 
 int main(int argc, const char *argv[]) {
   InitLLVM X(argc, argv);
+  ToolName = argv[0];
 
   // Register the target printer for --version.
   cl::AddExtraVersionPrinter(TargetRegistry::printRegisteredTargetsForVersion);