[COFF] Move section name encoding into BinaryFormat

Large COFF section names are moved into the string table and the
section header field is the offset into the string table encoded in
ASCII for offset smaller than 7 digits and in base64 for larger
offsets.

The operation of taking the string table offsets is done in a few
places in the codebase, so it is helpful to move this operation into
`BinaryFormat` so that it can be shared everywhere it's done.

So this patch takes the implementation of this operation from
`llvm/lib/MC/WinCOFFObjectWriter.cpp` and moves it into `BinaryFormat`.

Reviewed By: jhenderson, rnk

Differential Revision: https://reviews.llvm.org/D118793

1 files changed, 2 insertions, 39 deletions

diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index 0cbe51d..2af94b4 100644
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -451,32 +451,6 @@ void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
   Sym->MC = &MCSym;
 }
 
-// Maximum offsets for different string table entry encodings.
-enum : unsigned { Max7DecimalOffset = 9999999U };
-enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
-
-// Encode a string table entry offset in base 64, padded to 6 chars, and
-// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
-// Buffer must be at least 8 bytes large. No terminating null appended.
-static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
-  assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
-         "Illegal section name encoding for value");
-
-  static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-                                 "abcdefghijklmnopqrstuvwxyz"
-                                 "0123456789+/";
-
-  Buffer[0] = '/';
-  Buffer[1] = '/';
-
-  char *Ptr = Buffer + 7;
-  for (unsigned i = 0; i < 6; ++i) {
-    unsigned Rem = Value % 64;
-    Value /= 64;
-    *(Ptr--) = Alphabet[Rem];
-  }
-}
-
 void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
   if (S.Name.size() <= COFF::NameSize) {
     std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
@@ -484,19 +458,8 @@ void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
   }
 
   uint64_t StringTableEntry = Strings.getOffset(S.Name);
-  if (StringTableEntry <= Max7DecimalOffset) {
-    SmallVector<char, COFF::NameSize> Buffer;
-    Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
-    assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
-    std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
-    return;
-  }
-  if (StringTableEntry <= MaxBase64Offset) {
-    // Starting with 10,000,000, offsets are encoded as base64.
-    encodeBase64StringEntry(S.Header.Name, StringTableEntry);
-    return;
-  }
-  report_fatal_error("COFF string table is greater than 64 GB.");
+  if (!COFF::encodeSectionName(S.Header.Name, StringTableEntry))
+    report_fatal_error("COFF string table is greater than 64 GB.");
 }
 
 void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {