[llvm] r188884 - MC CFG: Add "dynamic disassembly" support to MCObjectDisassembler.

[David Blaikie]

On Wed, Aug 21, 2013 at 12:28 AM, Ahmed Bougacha
<ahmed.bougacha at gmail.com> wrote:
> Author: ab
> Date: Wed Aug 21 02:28:37 2013
> New Revision: 188884
>
> URL: http://llvm.org/viewvc/llvm-project?rev=188884&view=rev
> Log:
> MC CFG: Add "dynamic disassembly" support to MCObjectDisassembler.

Tests?

>
> It can now disassemble code in situations where the effective load
> address is different than the load address declared in the object file.
> This happens for PIC, hence "dynamic".
>
> Modified:
>     llvm/trunk/include/llvm/MC/MCObjectDisassembler.h
>     llvm/trunk/lib/MC/MCObjectDisassembler.cpp
>
> Modified: llvm/trunk/include/llvm/MC/MCObjectDisassembler.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCObjectDisassembler.h?rev=188884&r1=188883&r2=188884&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/MC/MCObjectDisassembler.h (original)
> +++ llvm/trunk/include/llvm/MC/MCObjectDisassembler.h Wed Aug 21 02:28:37 2013
> @@ -65,6 +65,22 @@ public:
>    virtual ArrayRef<uint64_t> getStaticExitFunctions();
>    /// @}
>
> +  /// \name Translation between effective and objectfile load address.
> +  /// @{
> +  /// \brief Compute the effective load address, from an objectfile virtual
> +  /// address. This is implemented in a format-specific way, to take into
> +  /// account things like PIE/ASLR when doing dynamic disassembly.
> +  /// For example, on Mach-O this would be done by adding the VM addr slide,
> +  /// on glibc ELF by keeping a map between segment load addresses, filled
> +  /// using dl_iterate_phdr, etc..
> +  /// In most static situations and in the default impl., this returns \p Addr.
> +  virtual uint64_t getEffectiveLoadAddr(uint64_t Addr);
> +
> +  /// \brief Compute the original load address, as specified in the objectfile.
> +  /// This is the inverse of getEffectiveLoadAddr.
> +  virtual uint64_t getOriginalLoadAddr(uint64_t EffectiveAddr);
> +  /// @}
> +
>  protected:
>    const object::ObjectFile &Obj;
>    const MCDisassembler &Dis;
>
> Modified: llvm/trunk/lib/MC/MCObjectDisassembler.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCObjectDisassembler.cpp?rev=188884&r1=188883&r2=188884&view=diff
> ==============================================================================
> --- llvm/trunk/lib/MC/MCObjectDisassembler.cpp (original)
> +++ llvm/trunk/lib/MC/MCObjectDisassembler.cpp Wed Aug 21 02:28:37 2013
> @@ -44,7 +44,7 @@ uint64_t MCObjectDisassembler::getEntryp
>      if (Name == "main" || Name == "_main") {
>        uint64_t Entrypoint;
>        SI->getAddress(Entrypoint);
> -      return Entrypoint;
> +      return getEffectiveLoadAddr(Entrypoint);
>      }
>    }
>    return 0;
> @@ -58,6 +58,14 @@ ArrayRef<uint64_t> MCObjectDisassembler:
>    return ArrayRef<uint64_t>();
>  }
>
> +uint64_t MCObjectDisassembler::getEffectiveLoadAddr(uint64_t Addr) {
> +  return Addr;
> +}
> +
> +uint64_t MCObjectDisassembler::getOriginalLoadAddr(uint64_t Addr) {
> +  return Addr;
> +}
> +
>  MCModule *MCObjectDisassembler::buildEmptyModule() {
>    MCModule *Module = new MCModule;
>    Module->Entrypoint = getEntrypoint();
> @@ -90,6 +98,7 @@ void MCObjectDisassembler::buildSectionA
>      uint64_t SecSize; SI->getSize(SecSize);
>      if (StartAddr == UnknownAddressOrSize || SecSize == UnknownAddressOrSize)
>        continue;
> +    StartAddr = getEffectiveLoadAddr(StartAddr);
>
>      StringRef Contents; SI->getContents(Contents);
>      StringRefMemoryObject memoryObject(Contents, StartAddr);
> @@ -170,6 +179,7 @@ void MCObjectDisassembler::buildCFG(MCMo
>      if (SymType == SymbolRef::ST_Function) {
>        uint64_t SymAddr;
>        SI->getAddress(SymAddr);
> +      SymAddr = getEffectiveLoadAddr(SymAddr);
>        Calls.insert(SymAddr);
>        Splits.insert(SymAddr);
>      }
>
>
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