1 files changed, 129 insertions, 3 deletions

diff --git a/llvm/tools/llvm-elfabi/ELFObjHandler.cpp b/llvm/tools/llvm-elfabi/ELFObjHandler.cpp
index 412c299c1f7..4c8e61db6ac 100644
--- a/llvm/tools/llvm-elfabi/ELFObjHandler.cpp
+++ b/llvm/tools/llvm-elfabi/ELFObjHandler.cpp
@@ -21,23 +21,149 @@ using llvm::object::ELFObjectFile;
 
 using namespace llvm;
 using namespace llvm::object;
-using namespace llvm::elfabi;
 using namespace llvm::ELF;
 
 namespace llvm {
 namespace elfabi {
 
+// Simple struct to hold relevant .dynamic entries.
+struct DynamicEntries {
+  uint64_t StrTabAddr = 0;
+  uint64_t StrSize = 0;
+  Optional<uint64_t> SONameOffset;
+};
+
+/// This function behaves similarly to StringRef::substr(), but attempts to
+/// terminate the returned StringRef at the first null terminator. If no null
+/// terminator is found, an error is returned.
+///
+/// @param Str Source string to create a substring from.
+/// @param Offset The start index of the desired substring.
+static Expected<StringRef> terminatedSubstr(StringRef Str, size_t Offset) {
+  size_t StrEnd = Str.find('\0', Offset);
+  if (StrEnd == StringLiteral::npos) {
+    return createError(
+        "String overran bounds of string table (no null terminator)");
+  }
+
+  size_t StrLen = StrEnd - Offset;
+  return Str.substr(Offset, StrLen);
+}
+
+/// This function takes an error, and appends a string of text to the end of
+/// that error. Since "appending" to an Error isn't supported behavior of an
+/// Error, this function technically creates a new error with the combined
+/// message and consumes the old error.
+///
+/// @param Err Source error.
+/// @param After Text to append at the end of Err's error message.
+Error appendToError(Error Err, StringRef After) {
+  std::string Message;
+  raw_string_ostream Stream(Message);
+  Stream << Err;
+  Stream << " " << After;
+  consumeError(std::move(Err));
+  return createError(Stream.str().c_str());
+}
+
+/// This function populates a DynamicEntries struct using an ELFT::DynRange.
+/// After populating the struct, the members are validated with
+/// some basic sanity checks.
+///
+/// @param Dyn Target DynamicEntries struct to populate.
+/// @param DynTable Source dynamic table.
+template <class ELFT>
+static Error populateDynamic(DynamicEntries &Dyn,
+                             typename ELFT::DynRange DynTable) {
+  if (DynTable.empty())
+    return createError("No .dynamic section found");
+
+  // Search .dynamic for relevant entries.
+  bool FoundDynStr = false;
+  bool FoundDynStrSz = false;
+  for (auto &Entry : DynTable) {
+    switch (Entry.d_tag) {
+    case DT_SONAME:
+      Dyn.SONameOffset = Entry.d_un.d_val;
+      break;
+    case DT_STRTAB:
+      Dyn.StrTabAddr = Entry.d_un.d_ptr;
+      FoundDynStr = true;
+      break;
+    case DT_STRSZ:
+      Dyn.StrSize = Entry.d_un.d_val;
+      FoundDynStrSz = true;
+      break;
+    }
+  }
+
+  if (!FoundDynStr) {
+    return createError(
+        "Couldn't locate dynamic string table (no DT_STRTAB entry)");
+  }
+  if (!FoundDynStrSz) {
+    return createError(
+        "Couldn't determine dynamic string table size (no DT_STRSZ entry)");
+  }
+  if (Dyn.SONameOffset.hasValue() && *Dyn.SONameOffset >= Dyn.StrSize) {
+    return createStringError(
+        object_error::parse_failed,
+        "DT_SONAME string offset (0x%016x) outside of dynamic string table",
+        *Dyn.SONameOffset);
+  }
+
+  return Error::success();
+}
+
 /// Returns a new ELFStub with all members populated from an ELFObjectFile.
 /// @param ElfObj Source ELFObjectFile.
 template <class ELFT>
-Expected<std::unique_ptr<ELFStub>>
+static Expected<std::unique_ptr<ELFStub>>
 buildStub(const ELFObjectFile<ELFT> &ElfObj) {
+  using Elf_Dyn_Range = typename ELFT::DynRange;
+  using Elf_Phdr_Range = typename ELFT::PhdrRange;
   std::unique_ptr<ELFStub> DestStub = make_unique<ELFStub>();
   const ELFFile<ELFT> *ElfFile = ElfObj.getELFFile();
+  // Fetch .dynamic table.
+  Expected<Elf_Dyn_Range> DynTable = ElfFile->dynamicEntries();
+  if (!DynTable) {
+    return DynTable.takeError();
+  }
+
+  // Fetch program headers.
+  Expected<Elf_Phdr_Range> PHdrs = ElfFile->program_headers();
+  if (!PHdrs) {
+    return PHdrs.takeError();
+  }
+
+  // Collect relevant .dynamic entries.
+  DynamicEntries DynEnt;
+  if (Error Err = populateDynamic<ELFT>(DynEnt, *DynTable))
+    return std::move(Err);
+
+  // Convert .dynstr address to an offset.
+  Expected<const uint8_t *> DynStrPtr =
+      ElfFile->toMappedAddr(DynEnt.StrTabAddr);
+  if (!DynStrPtr)
+    return appendToError(DynStrPtr.takeError(),
+                         "when locating .dynstr section contents");
 
+  StringRef DynStr(reinterpret_cast<const char *>(DynStrPtr.get()),
+                   DynEnt.StrSize);
+
+  // Populate Arch from ELF header.
   DestStub->Arch = ElfFile->getHeader()->e_machine;
 
-  // TODO: Populate SoName from .dynamic entries and linked string table.
+  // Populate SoName from .dynamic entries and dynamic string table.
+  if (DynEnt.SONameOffset.hasValue()) {
+    Expected<StringRef> NameOrErr =
+        terminatedSubstr(DynStr, *DynEnt.SONameOffset);
+    if (!NameOrErr) {
+      return appendToError(NameOrErr.takeError(), "when reading DT_SONAME");
+    }
+    DestStub->SoName = *NameOrErr;
+  }
+
   // TODO: Populate NeededLibs from .dynamic entries and linked string table.
   // TODO: Populate Symbols from .dynsym table and linked string table.