Address reviewer feedback.

 - Refactor warning message
 - Add testcase for unknown load command

Author: rjmansfield

llvm/lib/ObjectYAML/MachOEmitter.cpp

@@ -300,18 +300,18 @@ void MachOWriter::writeLoadCommands(raw_ostream &OS) {
     // specified test cases.
     // Prevent integer underflow if BytesWritten exceeds cmdsize.
     if (BytesWritten > LC.Data.load_command_data.cmdsize) {
-      const char *name = getLoadCommandName(LC.Data.load_command_data.cmd);
-      if (name)
-        WithColor::warning()
-            << "load command " << i << " " << name << " cmdsize too small ("
-            << LC.Data.load_command_data.cmdsize << " bytes) for actual size ("
-            << BytesWritten << " bytes)\n";
+      std::string Name;
+      const char *NameCStr = getLoadCommandName(LC.Data.load_command_data.cmd);
+      if (NameCStr)
+        Name = NameCStr;
       else
-        WithColor::warning()
-            << "load command " << i << " (0x"
-            << Twine::utohexstr(LC.Data.load_command_data.cmd)
-            << ") cmdsize too small (" << LC.Data.load_command_data.cmdsize
-            << " bytes) for actual size (" << BytesWritten << " bytes)\n";
+        Name = "(0x" + Twine::utohexstr(LC.Data.load_command_data.cmd).str() + ")";
+
+      WithColor::warning() << "load command " << i << " " << Name
+                           << " cmdsize too small ("
+                           << LC.Data.load_command_data.cmdsize
+                           << " bytes) for actual size (" << BytesWritten
+                           << " bytes)\n";
     }
     auto BytesRemaining = (BytesWritten < LC.Data.load_command_data.cmdsize)
                               ? LC.Data.load_command_data.cmdsize - BytesWritten

llvm/test/ObjectYAML/MachO/load-cmdsize-too-small.yaml

@@ -1,13 +1,18 @@
 ## Test that yaml2obj handles load commands with cmdsize smaller than the
 ## actual structure size without crashing (due to integer underflow).
 
-# RUN: yaml2obj %s -o %t 2>&1 | FileCheck %s --check-prefix=WARNING
-# RUN: not llvm-readobj --file-headers %t 2>&1 | FileCheck %s --check-prefix=MALFORMED
+# RUN: yaml2obj %s --docnum=1 -o %t1 2>&1 | FileCheck %s --check-prefix=WARNING-KNOWN
+# RUN: not llvm-readobj --file-headers %t1 2>&1 | FileCheck %s --check-prefix=MALFORMED
 
-# WARNING: warning: load command 0 LC_SEGMENT_64 cmdsize too small (56 bytes) for actual size (72 bytes)
+# RUN: yaml2obj %s --docnum=2 -o %t2 2>&1 | FileCheck %s --check-prefix=WARNING-UNKNOWN
+
+# WARNING-KNOWN: warning: load command 0 LC_SEGMENT_64 cmdsize too small (56 bytes) for actual size (72 bytes)
 
 # MALFORMED: error: {{.*}}: truncated or malformed object (load command 0 LC_SEGMENT_64 cmdsize too small)
 
+# WARNING-UNKNOWN: warning: load command 0 (0xdeadbeef) cmdsize too small (8 bytes) for actual size (20 bytes)
+
+## Test with a known load command (LC_SEGMENT_64)
 --- !mach-o
 FileHeader:
   magic:           0xFEEDFACF
@@ -31,3 +36,20 @@ LoadCommands:
     nsects:          0
     flags:           0
 ...
+
+## Test with an unknown load command value
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x01000007
+  cpusubtype:      0x00000003
+  filetype:        0x00000001
+  ncmds:           1
+  sizeofcmds:      20
+  flags:           0x00002000
+  reserved:        0x00000000
+LoadCommands:
+  - cmd:             0xDEADBEEF
+    cmdsize:         8
+    PayloadBytes:    [0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C]
+...