[lld] r344083 - Attempt to fix ubsan.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Tue Oct  9 14:41:53 2018
New Revision: 344083

URL: http://llvm.org/viewvc/llvm-project?rev=344083&view=rev
Log:
Attempt to fix ubsan.

Previously, we cast a pointer to Elf{32,64}_Chdr like this

  auto *Hdr = reinterpret_cast<const ELF64_Chdr>(Ptr);

and read from its members like this

  read32(&Hdr->ch_size);

I was thinking that this does not violate alignment requirement,
since &Hdr->ch_size doesn't really access memory, but seems like
it is a violation in terms of C++ spec (?)

In this patch, I use a different struct that allows unaligned access.

Modified:
    lld/trunk/ELF/InputSection.cpp

Modified: lld/trunk/ELF/InputSection.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=344083&r1=344082&r2=344083&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.cpp (original)
+++ lld/trunk/ELF/InputSection.cpp Tue Oct  9 14:41:53 2018
@@ -206,6 +206,9 @@ OutputSection *SectionBase::getOutputSec
 // by zlib-compressed data. This function parses a header to initialize
 // `UncompressedSize` member and remove the header from `RawData`.
 void InputSectionBase::parseCompressedHeader() {
+  typedef typename ELF64LE::Chdr Chdr64;
+  typedef typename ELF32LE::Chdr Chdr32;
+
   // Old-style header
   if (Name.startswith(".zdebug")) {
     if (!toStringRef(RawData).startswith("ZLIB")) {
@@ -233,35 +236,35 @@ void InputSectionBase::parseCompressedHe
 
   // New-style 64-bit header
   if (Config->Is64) {
-    if (RawData.size() < sizeof(Elf64_Chdr)) {
+    if (RawData.size() < sizeof(Chdr64)) {
       error(toString(this) + ": corrupted compressed section");
       return;
     }
 
-    auto *Hdr = reinterpret_cast<const Elf64_Chdr *>(RawData.data());
-    if (read32(&Hdr->ch_type) != ELFCOMPRESS_ZLIB) {
+    auto *Hdr = reinterpret_cast<const Chdr64 *>(RawData.data());
+    if (Hdr->ch_type != ELFCOMPRESS_ZLIB) {
       error(toString(this) + ": unsupported compression type");
       return;
     }
 
-    UncompressedSize = read64(&Hdr->ch_size);
+    UncompressedSize = Hdr->ch_size;
     RawData = RawData.slice(sizeof(*Hdr));
     return;
   }
 
   // New-style 32-bit header
-  if (RawData.size() < sizeof(Elf32_Chdr)) {
+  if (RawData.size() < sizeof(Chdr32)) {
     error(toString(this) + ": corrupted compressed section");
     return;
   }
 
-  auto *Hdr = reinterpret_cast<const Elf32_Chdr *>(RawData.data());
-  if (read32(&Hdr->ch_type) != ELFCOMPRESS_ZLIB) {
+  auto *Hdr = reinterpret_cast<const Chdr32 *>(RawData.data());
+  if (Hdr->ch_type != ELFCOMPRESS_ZLIB) {
     error(toString(this) + ": unsupported compression type");
     return;
   }
 
-  UncompressedSize = read32(&Hdr->ch_size);
+  UncompressedSize = Hdr->ch_size;
   RawData = RawData.slice(sizeof(*Hdr));
 }