[PATCH] MC: Support larger COFF string tables

[Nico Rieck]

  Clarified constants. Dropped base64 encoding.

Hi LegalizeAdulthood, asl, Bigcheese,

http://llvm-reviews.chandlerc.com/D667

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D667?vs=1835&id=3047#toc

Files:
  lib/MC/WinCOFFObjectWriter.cpp
  test/MC/COFF/section-name-encoding.s

Index: lib/MC/WinCOFFObjectWriter.cpp
===================================================================
--- lib/MC/WinCOFFObjectWriter.cpp
+++ lib/MC/WinCOFFObjectWriter.cpp
@@ -475,18 +475,21 @@
 /// name into the string table if needed
 void WinCOFFObjectWriter::MakeSectionReal(COFFSection &S, size_t Number) {
   if (S.Name.size() > COFF::NameSize) {
-    size_t StringTableEntry = Strings.insert(S.Name.c_str());
-
-    // FIXME: Why is this number 999999? This number is never mentioned in the
-    // spec. I'm assuming this is due to the printed value needing to fit into
-    // the S.Header.Name field. In which case why not 9999999 (7 9's instead of
-    // 6)? The spec does not state if this entry should be null terminated in
-    // this case, and thus this seems to be the best way to do it. I think I
-    // just solved my own FIXME...
-    if (StringTableEntry > 999999)
-      report_fatal_error("COFF string table is greater than 999999 bytes.");
-
-    std::sprintf(S.Header.Name, "/%d", unsigned(StringTableEntry));
+    const unsigned Max6DecimalSize = 999999;
+    const unsigned Max7DecimalSize = 9999999;
+    uint64_t StringTableEntry = Strings.insert(S.Name.c_str());
+
+    if (StringTableEntry <= Max6DecimalSize) {
+      std::sprintf(S.Header.Name, "/%d", unsigned(StringTableEntry));
+    } else if (StringTableEntry <= Max7DecimalSize) {
+      // With seven digits, we have to skip the terminating null. Because
+      // sprintf always appends it, we use a larger temporary buffer.
+      char buffer[9] = { };
+      std::sprintf(buffer, "/%d", unsigned(StringTableEntry));
+      std::memcpy(S.Header.Name, buffer, 8);
+    } else {
+      report_fatal_error("COFF string table is greater than 9,999,999 bytes.");
+    }
   } else
     std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
 
Index: test/MC/COFF/section-name-encoding.s
===================================================================
--- /dev/null
+++ test/MC/COFF/section-name-encoding.s
@@ -0,0 +1,30 @@
+// Check that COFF section names are properly encoded.
+//
+// Encodings for different lengths:
+//   [0, 8]:               raw name
+//   (8, 999999]:          base 10 string table index (/9999999)
+//
+// RUN: llvm-mc -triple x86_64-pc-win32 -filetype=obj %s | llvm-readobj -s | FileCheck %s
+
+// Raw encoding
+.section s;         f1: ret
+.section s1234567;  f2: ret
+
+// CHECK:   Section {
+// CHECK:     Number: 1
+// CHECK:     Name: s (73 00 00 00 00 00 00 00)
+// CHECK:   }
+// CHECK:   Section {
+// CHECK:     Number: 2
+// CHECK:     Name: s1234567 (73 31 32 33 34 35 36 37)
+// CHECK:   }
+
+
+// Base 10 encoding
+.section s12345678; f3: ret
+
+// /4
+// CHECK:   Section {
+// CHECK:     Number: 3
+// CHECK:     Name: s12345678 (2F 34 00 00 00 00 00 00)
+// CHECK:   }
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