[PATCH] D13621: [ELF2] Sort PPC64 special sections

[Rui Ueyama via llvm-commits]

ruiu added inline comments.

================
Comment at: ELF/Writer.cpp:356-382
@@ -343,3 +355,29 @@
   // nobits sections.
-  return A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS;
+  if (A->getType() != SHT_NOBITS && B->getType() == SHT_NOBITS)
+    return true;
+
+  // Check for the special ordering of special PPC64 section names.
+  auto PPC64NA =
+    std::find(PPC64SpecialNames, PPC64SpecialNamesEnd, A->getName());
+  auto PPC64NB =
+    std::find(PPC64SpecialNames, PPC64SpecialNamesEnd, B->getName());
+  // First, enforce the relative order in the PPC64SpecialNamesEnd array.
+  if (PPC64NA != PPC64SpecialNamesEnd &&
+      PPC64NB != PPC64SpecialNamesEnd &&
+      PPC64NA < PPC64NB)
+    return true;
+  // Second, any of the special PPC64 sections should come after other
+  // sections of the same type.
+  else if (PPC64NB != PPC64SpecialNames && /* not .got */
+           PPC64NB != PPC64SpecialNamesEnd &&
+           PPC64NA == PPC64SpecialNamesEnd)
+    return true;
+
+  // Conversely, the special .tocbss section should be first among all
+  // SHT_NOBITS sections. This will put it next to the loaded special
+  // PPC64 sections (and, thus, within reach of the TOC base pointer).
+  if (A->getName() == ".tocbss")
+    return true;
+
+  return false;
 }
----------------
You can simplify this by defining a function, say getPPCRank(StringRef), which returns an integer value according to this table.

  0 .tocbss
  1 any other name
  2 .toc
  3 .branch_lt
  4 .toc
  5 .toc1
  6 .opd

Then you can use that function in this function like this

  return getPPCRank(A) < getPPCRank(B);


http://reviews.llvm.org/D13621