[llvm-objdump] Document --mattr=help in --help output

[DavidSpickett]

Summary

This does the same as --mcpu=help but was only
documented in the user guide.

• Added a test for both options.
• Corrected the single dash in -mcpu=help text.

[DavidSpickett]

This is a follow up to discussion on: https://reviews.llvm.org/D92217

I have not updated the man page (llvm/docs/llvm-objdump.1) since it seems to have fallen behind in general. If you think it's worth updating the whole thing I'll do that as its own change, it's mostly replacing - with --.

(some talk about the manpage on https://reviews.llvm.org/D63606)

[jhenderson]

It's probably worth writing a test that shows how --mattr=help behaves (if it isn't tested already), given that it is being documented. If you'd prefer to do that in a separate patch, that's fine by me, or you can do it as part of this patch. The test would not want to be much more than that the help is printed when requested (it doesn't need to test the contents of the help output).

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

231–232

Please run clang-format on the modified code.

[DavidSpickett]

• Added test for mcpu/mattr=help
• clang-format

[jhenderson]

LGTM, once the two suggestions have been addressed.

llvm/test/tools/llvm-objdump/mattr-mcpu-help.test

8

Most newer binutils tests are using '##' as comment markers to help the comment stand out from the FileCheck and lit directives.

11

Not strictly required, but it enables users to add more yaml documents to the test should it ever get extended.

[DavidSpickett]

• Double # for comment
• Add dashes to ELF header

llvm/docs/CommandGuide/llvm-objdump.rst

 
 .. option:: --mcpu=<cpu-name>
 
   Target a specific CPU type for disassembly. Specify ``--mcpu=help`` to display
   available CPUs.
 
 .. option:: --mattr=<a1,+a2,-a3,...>
 
-  Enable/disable target-specific attributes. Specify ``--mcpu=help`` to display
+  Enable/disable target-specific attributes. Specify ``--mattr=help`` to display
   the available attributes.
 
 .. option:: --no-leading-addr
 
   When disassembling, do not print leading addresses.
 
 .. option:: --no-show-raw-insn
 

llvm/test/tools/llvm-objdump/mattr-mcpu-help.test

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objdump -d %t --mattr=help 2>&1 | FileCheck %s
+# RUN: llvm-objdump -d %t --mcpu=help 2>&1 | FileCheck %s
+
+# CHECK: Available CPUs for this target:
+# CHECK: Available features for this target:
+## To check we still disassemble the file:
+# CHECK: file format elf64-x86-64
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64

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

 
 static cl::opt<bool> MachOOpt("macho",
                               cl::desc("Use MachO specific object file parser"),
                               cl::cat(ObjdumpCat));
 static cl::alias MachOm("m", cl::desc("Alias for --macho"), cl::NotHidden,
                         cl::Grouping, cl::aliasopt(MachOOpt));
 
 cl::opt<std::string> objdump::MCPU(
-    "mcpu", cl::desc("Target a specific cpu type (-mcpu=help for details)"),
+    "mcpu", cl::desc("Target a specific cpu type (--mcpu=help for details)"),
     cl::value_desc("cpu-name"), cl::init(""), cl::cat(ObjdumpCat));
 
-cl::list<std::string> objdump::MAttrs("mattr", cl::CommaSeparated,
-                                      cl::desc("Target specific attributes"),
-                                      cl::value_desc("a1,+a2,-a3,..."),
-                                      cl::cat(ObjdumpCat));
+cl::list<std::string> objdump::MAttrs(
+    "mattr", cl::CommaSeparated,
+    cl::desc("Target specific attributes (--mattr=help for details)"),
+    cl::value_desc("a1,+a2,-a3,..."), cl::cat(ObjdumpCat));
 
 cl::opt<bool> objdump::NoShowRawInsn(
     "no-show-raw-insn",
     cl::desc(
         "When disassembling instructions, do not print the instruction bytes."),
     cl::cat(ObjdumpCat));
 
 cl::opt<bool> objdump::NoLeadingAddr("no-leading-addr",