Address reviewer comments

[kimanh]

Summary

Addressing reviewer comments:

• adding test on the header length, which changed test set
• removing accidentally added line in test
• removing obsolete comment
• update error messages to start with lower letter, and no new line

[kimanh]

Accidentally created new revision. Closing.

llvm/test/tools/llvm-dwp/X86/invalid_cu_header_length.s

 # RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o %t.o \
 # RUN:         -split-dwarf-file=%t.dwo -dwarf-version=5
 # RUN: not llvm-dwp %t.dwo -o %t.dwp 2>&1 | FileCheck %s
 
-# CHECK: error: Cannot parse compile unit length: unexpected end of data at offset 0x2 while reading [0x0, 0x4
-  .section  .debug_info.dwo,"e",@progbits
-  .short  0 # Length of Unit
+# CHECK: error: compile unit header exceeds .debug_info section range: 20 >= 6
+    .section  .debug_info.dwo,"e",@progbits
+    .long 16      # Length of Unit
+    .short 5      # Version
 No newline at end of file

llvm/test/tools/llvm-dwp/X86/invalid_cu_header_length_type.s

 # RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o %t.o \
 # RUN:         -split-dwarf-file=%t.dwo -dwarf-version=5
 # RUN: not llvm-dwp %t.dwo -o %t.dwp 2>&1 | FileCheck %s
 
-# CHECK: error: Cannot parse compile unit length: unexpected end of data at offset 0x2 while reading [0x0, 0x4
-  .section  .debug_info.dwo,"e",@progbits
-  .short  0 # Length of Unit
+# CHECK: error: cannot parse compile unit length: unexpected end of data at offset 0x2 while reading [0x0, 0x4
+    .section  .debug_info.dwo,"e",@progbits
+    .short  0 # Length of Unit

llvm/test/tools/llvm-dwp/X86/invalid_cu_header_unittype.s

-# RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o %t.o \
-# RUN:         -split-dwarf-file=%t.dwo -dwarf-version=5
-# RUN: not llvm-dwp %t.dwo -o %t.dwp 2>&1 | FileCheck %s
-
-# CHECK: error: Cannot parse compile unit header: unexpected end of data at offset 0x6 while reading [0x6, 0x7)
-  .section  .debug_info.dwo,"e",@progbits
-  .long 2 # Length of Unit
-  .short 5

llvm/test/tools/llvm-dwp/X86/invalid_cu_header_version.s

 # RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o %t.o \
 # RUN:         -split-dwarf-file=%t.dwo -dwarf-version=5
 # RUN: not llvm-dwp %t.dwo -o %t.dwp 2>&1 | FileCheck %s
 
-# CHECK: error: Cannot parse compile unit version: unexpected end of data at offset 0x4 while reading [0x4, 0x6)
-  .section  .debug_info.dwo,"e",@progbits
-  .long 0 # Length of Unit
+# CHECK: error: cannot parse compile unit version: unexpected end of data at offset 0x4 while reading [0x4, 0x6)
+    .section  .debug_info.dwo,"e",@progbits
+    .long 0 # Length of Unit

llvm/test/tools/llvm-dwp/X86/invalid_string_form.test

-RUN: not llvm-dwp %p/../Inputs/invalid_string_form.dwo -o %t 2>&1 | xargs echo
 RUN: not llvm-dwp %p/../Inputs/invalid_string_form.dwo -o %t 2>&1 | FileCheck %s
 
 CHECK: error: {{.*}}: string field must be encoded with one of the following:
 CHECK: DW_FORM_string, DW_FORM_strx, DW_FORM_strx1, DW_FORM_strx2, DW_FORM_strx3, DW_FORM_strx4, or DW_FORM_GNU_str_index.

llvm/test/tools/llvm-dwp/X86/unsupported_cu_index_version.s

 # RUN: llvm-mc -triple x86_64-unknown-linux %s -filetype=obj -o %t.dwp
 # RUN: not llvm-dwp %t.dwp -o %t 2>&1 | FileCheck %s
 
 # CHECK: error: unsupported cu_index version: 5 (only version 2 is supported)
-
-## To reach the test point, no real data is needed in .debug_info.dwo,
-## but the section should not be empty.
     .section .debug_info.dwo, "e", @progbits
     .long .Ldebug_info_dwo_end0-.Ldebug_info_dwo_start0 # Length of Unit
 .Ldebug_info_dwo_start0:
     .short 5                       # DWARF version number
     .byte 5                        # DWARF Unit type
     .byte 8                        # Address Size (in bytes)
     .long 0                        # Offset Into Abbrev. Section
     .quad -346972125991005518

llvm/tools/llvm-dwp/llvm-dwp.cpp

 static Expected<CompileUnitHeader> parseCompileUnitHeader(StringRef Info) {
   CompileUnitHeader Header;
   Error Err = Error::success();
   uint64_t Offset = 0;
   DWARFDataExtractor InfoData(Info, true, 0);
   std::tie(Header.Length, Header.Format) =
       InfoData.getInitialLength(&Offset, &Err);
   if (Err)
-    return make_error<DWPError>("Cannot parse compile unit length: " +
-                                llvm::toString(std::move(Err)) + "\n");
+    return make_error<DWPError>("cannot parse compile unit length: " +
+                                llvm::toString(std::move(Err)));
+
+  if (!InfoData.isValidOffset(Offset + (Header.Length - 1))) {
+    return make_error<DWPError>(
+        "compile unit header exceeds .debug_info section range: " +
+        utostr(Offset + Header.Length) + " >= " + utostr(InfoData.size()));
+  }
+
   Header.Version = InfoData.getU16(&Offset, &Err);
   if (Err)
-    return make_error<DWPError>("Cannot parse compile unit version: " +
-                                llvm::toString(std::move(Err)) + "\n");
+    return make_error<DWPError>("cannot parse compile unit version: " +
+                                llvm::toString(std::move(Err)));
+
+  uint64_t MinHeaderLength;
+  if (Header.Version >= 5) {
+    // Size: Version (2), UnitType (1), AddrSize (1), DebugAbbrevOffset (4),
+    // Signature (8)
+    MinHeaderLength = 16;
+  } else {
+    // Size: Version (2), DebugAbbrevOffset (4), AddrSize (1)
+    MinHeaderLength = 7;
+  }
+  if (Header.Length < MinHeaderLength) {
+    return make_error<DWPError>(
+        "compile unit length is too small: expected at least " +
+        utostr(MinHeaderLength) + " got " + utostr(Header.Length) + ".");
+  }
+
   if (Header.Version >= 5) {
     Header.UnitType = InfoData.getU8(&Offset, &Err);
     Header.AddrSize = InfoData.getU8(&Offset, &Err);
     Header.DebugAbbrevOffset = InfoData.getU32(&Offset, &Err);
     Header.Signature = InfoData.getU64(&Offset, &Err);
   } else {
     // Note that, address_size and debug_abbrev_offset fields have switched
     // places between dwarf version 4 and 5.
     Header.DebugAbbrevOffset = InfoData.getU32(&Offset, &Err);
     Header.AddrSize = InfoData.getU8(&Offset, &Err);
   }
-  if (Err)
-    return make_error<DWPError>("Cannot parse compile unit header: " +
-                                llvm::toString(std::move(Err)) + "\n");
+  assert(!Err && "Compile unit header is missing fields");
+
   Header.HeaderSize = Offset;
   return Header;
 }
 
 static void writeStringsAndOffsets(MCStreamer &Out, DWPStringPool &Strings,
                                    MCSection *StrOffsetSection,
                                    StringRef CurStrSection,
                                    StringRef CurStrOffsetSection,