Subzero: Write float/double constant pools directly to the ELF file.
Create the section, write the data and define the symbols in
the symbol table.
BUG=none
R=stichnot@chromium.org
Review URL: https://codereview.chromium.org/837393005
diff --git a/src/IceELFObjectWriter.cpp b/src/IceELFObjectWriter.cpp
index 3ac8a55..4a31a99 100644
--- a/src/IceELFObjectWriter.cpp
+++ b/src/IceELFObjectWriter.cpp
@@ -17,6 +17,7 @@
#include "IceELFStreamer.h"
#include "IceGlobalContext.h"
#include "IceGlobalInits.h"
+#include "IceOperand.h"
using namespace llvm::ELF;
@@ -291,6 +292,61 @@
Str.writeLE16(static_cast<Elf64_Half>(SectHeaderStrIndex)); // e_shstrndx
}
+template <typename ConstType> void ELFObjectWriter::writeConstantPool(Type Ty) {
+ ConstantList Pool = Ctx.getConstantPool(Ty);
+ if (Pool.empty()) {
+ return;
+ }
+ SizeT Align = typeAlignInBytes(Ty);
+ size_t EntSize = typeWidthInBytes(Ty);
+ char Buf[20];
+ SizeT WriteAmt = std::min(EntSize, llvm::array_lengthof(Buf));
+ assert(WriteAmt == EntSize);
+ // Assume that writing WriteAmt bytes at a time allows us to avoid aligning
+ // between entries.
+ assert(WriteAmt % Align == 0);
+ // Check that we write the full PrimType.
+ assert(WriteAmt == sizeof(typename ConstType::PrimType));
+ const Elf64_Xword ShFlags = SHF_ALLOC | SHF_MERGE;
+ std::string SecBuffer;
+ llvm::raw_string_ostream SecStrBuf(SecBuffer);
+ SecStrBuf << ".rodata.cst" << WriteAmt;
+ ELFDataSection *Section = createSection<ELFDataSection>(
+ SecStrBuf.str(), SHT_PROGBITS, ShFlags, Align, WriteAmt);
+ RoDataSections.push_back(Section);
+ SizeT OffsetInSection = 0;
+ // The symbol table entry doesn't need to know the defined symbol's
+ // size since this is in a section with a fixed Entry Size.
+ const SizeT SymbolSize = 0;
+ Section->setFileOffset(alignFileOffset(Align));
+
+ // Write the data.
+ for (Constant *C : Pool) {
+ auto Const = llvm::cast<ConstType>(C);
+ std::string SymBuffer;
+ llvm::raw_string_ostream SymStrBuf(SymBuffer);
+ SymStrBuf << ".L$" << Ty << "$" << Const->getPoolEntryID();
+ std::string &SymName = SymStrBuf.str();
+ SymTab->createDefinedSym(SymName, STT_NOTYPE, STB_LOCAL, Section,
+ OffsetInSection, SymbolSize);
+ StrTab->add(SymName);
+ typename ConstType::PrimType Value = Const->getValue();
+ memcpy(Buf, &Value, WriteAmt);
+ Str.writeBytes(llvm::StringRef(Buf, WriteAmt));
+ OffsetInSection += WriteAmt;
+ }
+ Section->setSize(OffsetInSection);
+}
+
+// Instantiate known needed versions of the template, since we are
+// defining the function in the .cpp file instead of the .h file.
+// We may need to instantiate constant pools for integers as well
+// if we do constant-pooling of large integers to remove them
+// from the instruction stream (fewer bytes controlled by an attacker).
+template void ELFObjectWriter::writeConstantPool<ConstantFloat>(Type Ty);
+
+template void ELFObjectWriter::writeConstantPool<ConstantDouble>(Type Ty);
+
void ELFObjectWriter::writeNonUserSections() {
bool IsELF64 = isELF64(Ctx.getTargetArch());
