[DWARF] Use getInitialLength in range list parsing

[labath]

Summary

This could be considered obvious, but I am putting it up to illustrate
the usefulness/impact of the getInitialLength change.

[probinson]

My goodness that is so much easier to read! LGTM

[jhenderson]

LGTM too, although I guess this might need rebasing due to the recent error message improvement?

[labath]

In D75117#1897400, @jhenderson wrote:

LGTM too, although I guess this might need rebasing due to the recent error message improvement?

Yes, I'll do that before committing. Thanks for all the reviews.

llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp

 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
 Error DWARFListTableHeader::extract(DWARFDataExtractor Data,
                                     uint64_t *OffsetPtr) {
   HeaderOffset = *OffsetPtr;
-  // Read and verify the length field.
-  if (!Data.isValidOffsetForDataOfSize(*OffsetPtr, sizeof(uint32_t)))
-    return createStringError(errc::invalid_argument,
-                       "section is not large enough to contain a "
-                       "%s table length at offset 0x%" PRIx64,
-                       SectionName.data(), *OffsetPtr);
-  Format = dwarf::DwarfFormat::DWARF32;
-  uint8_t OffsetByteSize = 4;
-  HeaderData.Length = Data.getRelocatedValue(4, OffsetPtr);
-  if (HeaderData.Length == dwarf::DW_LENGTH_DWARF64) {
-    Format = dwarf::DwarfFormat::DWARF64;
-    OffsetByteSize = 8;
-    HeaderData.Length = Data.getU64(OffsetPtr);
-  } else if (HeaderData.Length >= dwarf::DW_LENGTH_lo_reserved) {
-    return createStringError(errc::invalid_argument,
-        "%s table at offset 0x%" PRIx64
-        " has unsupported reserved unit length of value 0x%8.8" PRIx64,
-        SectionName.data(), HeaderOffset, HeaderData.Length);
-  }
+  Error Err = Error::success();
+
+  std::tie(HeaderData.Length, Format) = Data.getInitialLength(OffsetPtr, &Err);
+  if (Err)
+    return createStringError(
+        errc::invalid_argument, "parsing %s table at offset 0x%" PRIx64 ": %s",
+        SectionName.data(), HeaderOffset, toString(std::move(Err)).c_str());
+
+  uint8_t OffsetByteSize = Format == dwarf::DWARF64 ? 8 : 4;
   uint64_t FullLength =
       HeaderData.Length + dwarf::getUnitLengthFieldByteSize(Format);
   assert(FullLength == length());
   if (FullLength < getHeaderSize(Format))
     return createStringError(errc::invalid_argument,
                        "%s table at offset 0x%" PRIx64
                        " has too small length (0x%" PRIx64
                        ") to contain a complete header",

llvm/test/tools/llvm-dwarfdump/X86/debug_rnglists_invalid.s

 # RUN: llvm-mc %S/Inputs/debug_rnglists_short_section.s -filetype obj -triple x86_64-pc-linux -o - | \
 # RUN: llvm-dwarfdump --debug-rnglists - 2>&1 | FileCheck %s --check-prefix=SHORT
 # SHORT-NOT: error:
 # SHORT-NOT: range list header
-# SHORT: error: section is not large enough to contain a .debug_rnglists table length at offset 0
+# SHORT: error: parsing .debug_rnglists table at offset 0x0: unexpected end of data
 # SHORT-NOT: range list header
 # SHORT-NOT: error:
 
 # RUN: llvm-mc %s -filetype obj -triple x86_64-pc-linux -o - | \
 # RUN: llvm-dwarfdump --debug-rnglists - 2> %t.err | FileCheck %s --check-prefix=GOOD
 # RUN: FileCheck %s --input-file %t.err
 
 # GOOD: .debug_rnglists contents:

llvm/test/tools/llvm-dwarfdump/X86/debug_rnglists_reserved_length.s

 # RUN: llvm-mc %s -filetype obj -triple x86_64-pc-linux -o - | \
 # RUN:   llvm-dwarfdump --debug-rnglists - 2>&1 | \
 # RUN:   FileCheck %s --implicit-check-not=error
 
-# CHECK: error: .debug_rnglists table at offset 0x0 has unsupported reserved unit length of value 0xfffffff0
+# CHECK: error: parsing .debug_rnglists table at offset 0x0: unsupported reserved unit length of value 0xfffffff0
 
 .section .debug_rnglists,"",@progbits
 .long 0xfffffff0