[PATCH] D51065: [WebAssembly] Ensure relocation are entries are ordered by offset

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: llvm-commits, mgrang, sunfish, aheejin, jgravelle-google, dschuff.

I don't have an example for how to create such out-of-order
relocations although I've seen them exist in the wild.  I'd
like to hold off landing this until I can find an example
or test case.


Repository:
  rL LLVM

https://reviews.llvm.org/D51065

Files:
  lib/MC/WasmObjectWriter.cpp
  lib/Object/WasmObjectFile.cpp


Index: lib/Object/WasmObjectFile.cpp
===================================================================
--- lib/Object/WasmObjectFile.cpp
+++ lib/Object/WasmObjectFile.cpp
@@ -602,10 +602,15 @@
   WasmSection& Section = Sections[SectionIndex];
   uint32_t RelocCount = readVaruint32(Ctx);
   uint32_t EndOffset = Section.Content.size();
+  uint32_t PreviousOffset = 0;
   while (RelocCount--) {
     wasm::WasmRelocation Reloc = {};
     Reloc.Type = readVaruint32(Ctx);
     Reloc.Offset = readVaruint32(Ctx);
+    if (Reloc.Offset < PreviousOffset)
+      return make_error<GenericBinaryError>("Relocations not in offset order"
+                                            object_error::parse_failed);
+    PreviousOffset = Reloc.Offset;
     Reloc.Index = readVaruint32(Ctx);
     switch (Reloc.Type) {
     case wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
Index: lib/MC/WasmObjectWriter.cpp
===================================================================
--- lib/MC/WasmObjectWriter.cpp
+++ lib/MC/WasmObjectWriter.cpp
@@ -306,7 +306,7 @@
                         ArrayRef<WasmFunction> Functions);
   void writeDataSection();
   void writeRelocSection(uint32_t SectionIndex, StringRef Name,
-                         ArrayRef<WasmRelocationEntry> Relocations);
+                         std::vector<WasmRelocationEntry>& Relocations);
   void writeLinkingMetaDataSection(
       ArrayRef<wasm::WasmSymbolInfo> SymbolInfos,
       ArrayRef<std::pair<uint16_t, uint32_t>> InitFuncs,
@@ -892,19 +892,26 @@
 
 void WasmObjectWriter::writeRelocSection(
     uint32_t SectionIndex, StringRef Name,
-    ArrayRef<WasmRelocationEntry> Relocations) {
+    std::vector<WasmRelocationEntry>& Relocs) {
   // See: https://github.com/WebAssembly/tool-conventions/blob/master/Linking.md
   // for descriptions of the reloc sections.
 
-  if (Relocations.empty())
+  if (Relocs.empty())
     return;
 
   SectionBookkeeping Section;
   startCustomSection(Section, std::string("reloc.") + Name.str());
 
+  // 
+  llvm::sort(Relocs.begin(), Relocs.end(),
+             [](const WasmRelocationEntry &A, const WasmRelocationEntry &B) {
+               return (A.Offset + A.FixupSection->getSectionOffset()) <
+                      (B.Offset + B.FixupSection->getSectionOffset());
+             });
+
   encodeULEB128(SectionIndex, W.OS);
-  encodeULEB128(Relocations.size(), W.OS);
-  for (const WasmRelocationEntry& RelEntry : Relocations) {
+  encodeULEB128(Relocs.size(), W.OS);
+  for (const WasmRelocationEntry& RelEntry : Relocs) {
     uint64_t Offset = RelEntry.Offset +
                       RelEntry.FixupSection->getSectionOffset();
     uint32_t Index = getRelocationIndexValue(RelEntry);


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