[llvm-objdump] Keep warning for --disassemble-functions in correct order.

[ychen]

Summary

relative to normal output when dumping archive files.

prepare for PR41911.

[MaskRay]

LG. A few nits below:

llvm/test/tools/llvm-objdump/X86/warn-missing-disasm-func.test

6

yaml2obj -o %t.o %s
rm -f %t.a
llvm-ar qc %t.a %t.o %t.o

llvm/tools/llvm-objdump/llvm-objdump.cpp

384

Why was StringRef Prefix added? It does not seem to be used.

389

This is probably redundant. stderr is by default unbuffered. If the user makes it buffered, they should be prepared to see out-of-order output.

[jhenderson]

LGTM, with MaskRay's comments addressed.

[ychen]

• update

[ychen]

llvm/tools/llvm-objdump/llvm-objdump.cpp

384

It was intended for the patch for PR35351. I've removed it.

389

Agree that it seems redundant but it makes explicit that stderr should be flushed there. Three other places in the same file use it too. I could remove them all or keep them all otherwise it is really confusing and inconsistent. Thoughts?

[ychen]

llvm/tools/llvm-objdump/llvm-objdump.cpp

384

I meant to say PR41911.

llvm/test/tools/llvm-objdump/X86/warn-missing-disasm-func.test

 ## Warn if --disassemble-functions specifies an unknown symbol.
-# RUN: yaml2obj %s | llvm-objdump - --disassemble-functions=foo 2>&1 | FileCheck %s
+
+# RUN: yaml2obj -o %t.1.o %s
+# RUN: yaml2obj -o %t.2.o %s
+# RUN: rm -f %t.a
+# RUN: llvm-ar rc %t.a %t.1.o %t.2.o
+# RUN: llvm-objdump --disassemble-functions=foo %t.1.o 2>&1 | FileCheck %s
+# RUN: llvm-objdump --disassemble-functions=foo %t.a 2>&1 | FileCheck %s --check-prefix=MULTI
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_X86_64
 
 # CHECK: warning: failed to disassemble missing function foo
+
+# MULTI: file format ELF64-x86-64
+# MULTI: warning: failed to disassemble missing function foo
+# MULTI: file format ELF64-x86-64
+# MULTI: warning: failed to disassemble missing function foo

llvm/tools/llvm-objdump/llvm-objdump.cpp

LLVM_ATTRIBUTE_NORETURN void error(Twine Message) {
   exit(1);
 }
 
 void warn(StringRef Message) {
   WithColor::warning(errs(), ToolName) << Message << ".\n";
   errs().flush();
 }
 
-void warn(Twine Message) {
-  WithColor::warning(errs(), ToolName) << Message << "\n";
+static void warn(Twine Message, StringRef Prefix = "") {
+  // Output order between errs() and outs() matters especially for archive
+  // files where the output is per member object.
+  outs().flush();
+  WithColor::warning(errs(), Prefix) << Message << "\n";
+  errs().flush();
 }
 
 LLVM_ATTRIBUTE_NORETURN void report_error(StringRef File, Twine Message) {
   WithColor::error(errs(), ToolName)
       << "'" << File << "': " << Message << ".\n";
   exit(1);
 }