Enable x86 support for Unix

Also enabled cross compilation of x86 binaries on x64 host.

Ubuntu Dockerfiles:

<details>
  <summary><b><ins>Baseline: x64 build on x64 host</ins></b></summary>

```dockerfile
FROM ubuntu
RUN cat /etc/*-release

RUN apt-get update
RUN apt-get install -y \
        autoconf bash clang cmake gcc libtool curl \
        libunwind-dev llvm make openssl lldb git uuid-dev

RUN git clone https://github.com/dotnet/corert -b master --single-branch

WORKDIR /corert

RUN ./build.sh          # or ./build.sh x64

```
</details>

<details>
  <summary><b><ins>PR: x86 build on x86 host</ins></b></summary>

```dockerfile
FROM i386/ubuntu
RUN cat /etc/*-release

RUN apt-get update
RUN apt-get install -y \
        bash clang cmake gcc libtool curl \
        libunwind-dev llvm make openssl lldb git uuid-dev

RUN git clone https://github.com/am11/corert -b linux-x86 --single-branch

WORKDIR /corert

RUN ./build.sh x86
```
</details>

<details>
  <summary><b><ins>PR: x86 build on x64 host</ins></b></summary>

```dockerfile
FROM ubuntu
RUN cat /etc/*-release

RUN apt-get update
RUN apt-get install -y \
        bash clang cmake gcc libtool curl \
        libunwind-dev llvm make openssl lldb git uuid-dev \
        g++-multilib

RUN git clone https://github.com/am11/corert -b linux-x86 --single-branch

WORKDIR /corert

RUN ./build.sh x86
```
</details>

25 files changed, 241 insertions, 34 deletions

diff --git a/src/Native/CMakeLists.txt b/src/Native/CMakeLists.txt
index c486248fb..ad55c469f 100644
--- a/src/Native/CMakeLists.txt
+++ b/src/Native/CMakeLists.txt
@@ -22,11 +22,11 @@ function(clr_unknown_arch)
     if (WIN32)
         message(FATAL_ERROR "Only AMD64 and I386 are supported")
     else()
-        message(FATAL_ERROR "Only AMD64, ARM64, ARM and ARMEL are supported")
+        message(FATAL_ERROR "Only AMD64, ARM64, ARM, ARMEL and I386 are supported")
     endif()
 endfunction()
 
-if (CMAKE_SYSTEM_PROCESSOR STREQUAL x86_64 OR CMAKE_SYSTEM_PROCESSOR STREQUAL amd64)
+if (CLR_CMAKE_TARGET_ARCH STREQUAL x64 OR CLR_CMAKE_TARGET_ARCH STREQUAL arm64)
     set(IS_64BIT_BUILD 1)
 elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL armv7l)
     add_definitions(-DBIT32=1)
@@ -60,12 +60,14 @@ endif(CMAKE_SYSTEM_NAME STREQUAL Darwin)
 
 if(CMAKE_SYSTEM_NAME STREQUAL Linux)
     set(CLR_CMAKE_PLATFORM_UNIX 1)
-    if(CMAKE_SYSTEM_PROCESSOR STREQUAL x86_64)
+    if(CLR_CMAKE_TARGET_ARCH STREQUAL x64)
         set(CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64 1)
-    elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL armv7l)
+    elseif(CLR_CMAKE_TARGET_ARCH STREQUAL arm)
         set(CLR_CMAKE_PLATFORM_UNIX_TARGET_ARM 1)
-    elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64)
+    elseif(CLR_CMAKE_TARGET_ARCH STREQUAL arm64)
         set(CLR_CMAKE_PLATFORM_UNIX_TARGET_ARM64 1)
+    elseif(CLR_CMAKE_TARGET_ARCH STREQUAL x86)
+        set(CLR_CMAKE_PLATFORM_UNIX_TARGET_I386 1)
     else()
         clr_unknown_arch()
     endif()
@@ -99,10 +101,15 @@ if (CLR_CMAKE_PLATFORM_UNIX)
     add_compile_options(-Wno-null-arithmetic)
     add_compile_options(-Wno-null-conversion)
 
-    if (CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64)
+    if (CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64 OR CLR_CMAKE_PLATFORM_UNIX_TARGET_I386)
         # Allow 16 byte compare-exchange
         add_compile_options(-mcx16)
+    endif()
+
+    if (CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64)
         add_definitions(-DUNIX_AMD64_ABI)
+    elseif (CLR_CMAKE_PLATFORM_UNIX_TARGET_I386)
+        add_definitions(-DUNIX_X86_ABI)
     endif()
 
     # Disable strict warning on unused functions.
@@ -122,7 +129,7 @@ if (CLR_CMAKE_PLATFORM_UNIX)
     endif(CLR_CMAKE_PLATFORM_DARWIN)
 
     if(CLR_CMAKE_PLATFORM_LINUX)
-        set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -Wa,--noexecstack")  
+        set(CMAKE_ASM_FLAGS "${CMAKE_ASM_FLAGS} -Wa,--noexecstack")
     endif(CLR_CMAKE_PLATFORM_LINUX)
 endif(CLR_CMAKE_PLATFORM_UNIX)
 
@@ -132,6 +139,8 @@ elseif(CLR_CMAKE_PLATFORM_UNIX_TARGET_ARM64)
     set(CLR_CMAKE_PLATFORM_ARCH_ARM64 1)
 elseif(CLR_CMAKE_PLATFORM_UNIX_TARGET_AMD64)
     set(CLR_CMAKE_PLATFORM_ARCH_AMD64 1)
+elseif(CLR_CMAKE_PLATFORM_UNIX_TARGET_I386)
+    set(CLR_CMAKE_PLATFORM_ARCH_I386 1)
 elseif(WIN32)
     if (CLR_CMAKE_TARGET_ARCH STREQUAL x64)
         set(CLR_CMAKE_PLATFORM_ARCH_AMD64 1)
@@ -161,7 +170,7 @@ function(get_compile_definitions DefinitionName)
 
     foreach(DEFINITION IN LISTS COMPILE_DEFINITIONS_LIST)
         if (${DEFINITION} MATCHES "^\\$<\\$<CONFIG:([^>]+)>:([^>]+)>$")
-            # The entries that contain generator expressions must have the -D inside of the 
+            # The entries that contain generator expressions must have the -D inside of the
             # expression. So we transform e.g. $<$<CONFIG:Debug>:_DEBUG> to $<$<CONFIG:Debug>:-D_DEBUG>
             set(DEFINITION "$<$<CONFIG:${CMAKE_MATCH_1}>:-D${CMAKE_MATCH_2}>")
         else()
@@ -189,8 +198,8 @@ else()
 endif()
 
 # Set the passed in RetSources variable to the list of sources with added current source directory
-# to form absolute paths. 
-# The parameters after the RetSources are the input files. 
+# to form absolute paths.
+# The parameters after the RetSources are the input files.
 function(convert_to_absolute_path RetSources)
     set(Sources ${ARGN})
     foreach(Source IN LISTS Sources)
@@ -222,6 +231,10 @@ elseif (UPPERCASE_CMAKE_BUILD_TYPE STREQUAL RELEASE)
 else ()
     message(FATAL_ERROR "Unknown build type. Set CMAKE_BUILD_TYPE to DEBUG or RELEASE.")
 endif ()
+if (CLR_CMAKE_PLATFORM_ARCH_I386)
+    add_compile_options(-m32)
+    link_libraries(-m32)
+endif()
 endif (WIN32)
 
 include(configure.cmake)
diff --git a/src/Native/Runtime/CMakeLists.txt b/src/Native/Runtime/CMakeLists.txt
index ecf44f0ce..24536e364 100644
--- a/src/Native/Runtime/CMakeLists.txt
+++ b/src/Native/Runtime/CMakeLists.txt
@@ -42,7 +42,7 @@ set(COMMON_RUNTIME_SOURCES
     thread.cpp
     threadstore.cpp
     UniversalTransitionHelpers.cpp
-    
+
     ../gc/gccommon.cpp
     ../gc/gceewks.cpp
     ../gc/gcwks.cpp
@@ -124,15 +124,15 @@ else()
     )
   endif()
 
+  set(ASM_SUFFIX S)
   if(CLR_CMAKE_PLATFORM_ARCH_AMD64)
     set(ARCH_SOURCES_DIR amd64)
-    set(ASM_SUFFIX S)
   elseif(CLR_CMAKE_PLATFORM_ARCH_ARM64)
     set(ARCH_SOURCES_DIR arm64)
-    set(ASM_SUFFIX S)
   elseif(CLR_CMAKE_PLATFORM_ARCH_ARM)
     set(ARCH_SOURCES_DIR arm)
-    set(ASM_SUFFIX S)
+  elseif(CLR_CMAKE_PLATFORM_ARCH_I386)
+    set(ARCH_SOURCES_DIR i386)
   endif()
 
   list(APPEND RUNTIME_SOURCES_ARCH_ASM
@@ -148,7 +148,7 @@ list(APPEND RUNTIME_SOURCES_ARCH_ASM
   ${ARCH_SOURCES_DIR}/ExceptionHandling.${ASM_SUFFIX}
   ${ARCH_SOURCES_DIR}/Interlocked.${ASM_SUFFIX}
   ${ARCH_SOURCES_DIR}/PInvoke.${ASM_SUFFIX}
-  ${ARCH_SOURCES_DIR}/InteropThunksHelpers.${ASM_SUFFIX}  
+  ${ARCH_SOURCES_DIR}/InteropThunksHelpers.${ASM_SUFFIX}
   ${ARCH_SOURCES_DIR}/StubDispatch.${ASM_SUFFIX}
   ${ARCH_SOURCES_DIR}/UniversalTransition.${ASM_SUFFIX}
   ${ARCH_SOURCES_DIR}/WriteBarriers.${ASM_SUFFIX}
diff --git a/src/Native/Runtime/PalRedhawk.h b/src/Native/Runtime/PalRedhawk.h
index 86d0ee917..0dc30f19d 100644
--- a/src/Native/Runtime/PalRedhawk.h
+++ b/src/Native/Runtime/PalRedhawk.h
@@ -31,7 +31,7 @@
 #endif
 
 #ifndef _INC_WINDOWS
-//#ifndef DACCESS_COMPILE 
+//#ifndef DACCESS_COMPILE
 
 // There are some fairly primitive type definitions below but don't pull them into the rest of Redhawk unless
 // we have to (in which case these definitions will move to CommonTypes.h).
@@ -807,7 +807,7 @@ typedef UInt32 (__stdcall *BackgroundCallback)(_In_opt_ void* pCallbackContext);
 REDHAWK_PALIMPORT bool REDHAWK_PALAPI PalStartBackgroundGCThread(_In_ BackgroundCallback callback, _In_opt_ void* pCallbackContext);
 REDHAWK_PALIMPORT bool REDHAWK_PALAPI PalStartFinalizerThread(_In_ BackgroundCallback callback, _In_opt_ void* pCallbackContext);
 
-typedef UInt32 (__stdcall *PalHijackCallback)(HANDLE hThread, _In_ PAL_LIMITED_CONTEXT* pThreadContext, _In_opt_ void* pCallbackContext);
+typedef UInt32_BOOL (*PalHijackCallback)(HANDLE hThread, _In_ PAL_LIMITED_CONTEXT* pThreadContext, _In_opt_ void* pCallbackContext);
 REDHAWK_PALIMPORT UInt32 REDHAWK_PALAPI PalHijack(HANDLE hThread, _In_ PalHijackCallback callback, _In_opt_ void* pCallbackContext);
 
 #ifdef FEATURE_ETW
diff --git a/src/Native/Runtime/PalRedhawkCommon.h b/src/Native/Runtime/PalRedhawkCommon.h
index 4edab876b..5166ad4b4 100644
--- a/src/Native/Runtime/PalRedhawkCommon.h
+++ b/src/Native/Runtime/PalRedhawkCommon.h
@@ -134,6 +134,8 @@ struct PAL_LIMITED_CONTEXT
     UIntNative GetIp() const { return IP; }
     UIntNative GetSp() const { return Rsp; }
     UIntNative GetFp() const { return Rbp; }
+    void SetIp(UIntNative ip) { IP = ip; }
+    void SetSp(UIntNative sp) { Rsp = sp; }
 #endif // _TARGET_ARM_
 };
 
diff --git a/src/Native/Runtime/coreclr/bitvector.h b/src/Native/Runtime/coreclr/bitvector.h
index a4181dbb8..0f273dbac 100644
--- a/src/Native/Runtime/coreclr/bitvector.h
+++ b/src/Native/Runtime/coreclr/bitvector.h
@@ -12,7 +12,6 @@
 #ifndef BITVECTOR_H
 #define BITVECTOR_H 1
 
-
 #ifndef LIMITED_METHOD_CONTRACT
 #define LIMITED_METHOD_CONTRACT
 #define UNDEF_LIMITED_METHOD_CONTRACT
@@ -60,8 +59,9 @@
 class BitVector {
     // Set this to be unsigned char to do testing, should be UINT_PTR for real life
 
-    typedef UINT_PTR ChunkType;  // The size of integer type that the machine can operate on directly  
-//  typedef BYTE ChunkType;      // Use for testing
+    typedef uint32_t BOOL;
+    typedef uintptr_t ChunkType;  // The size of integer type that the machine can operate on directly
+//  typedef BYTE ChunkType;       // Use for testing
 
     // Maximum number of bits in our bitvector
 #define MAX_PTRARG_OFS 1024
diff --git a/src/Native/Runtime/coreclr/gcinfotypes.h b/src/Native/Runtime/coreclr/gcinfotypes.h
index c802d97ec..9b949b55f 100644
--- a/src/Native/Runtime/coreclr/gcinfotypes.h
+++ b/src/Native/Runtime/coreclr/gcinfotypes.h
@@ -18,12 +18,11 @@
 
 #define BITS_PER_SIZE_T ((int)sizeof(size_t)*8)
 
-
 //--------------------------------------------------------------------------------
-// It turns out, that ((size_t)x) << y == x, when y is not a literal 
+// It turns out, that ((size_t)x) << y == x, when y is not a literal
 //      and its value is BITS_PER_SIZE_T
 // I guess the processor only shifts of the right operand modulo BITS_PER_SIZE_T
-// In many cases, we want the above operation to yield 0, 
+// In many cases, we want the above operation to yield 0,
 //      hence the following macros
 //--------------------------------------------------------------------------------
 __forceinline size_t SAFE_SHIFT_LEFT(size_t x, size_t count)
@@ -346,7 +345,7 @@ enum infoHdrAdjustConstants {
     SET_RET_KIND_MAX = 4,   // 2 bits for ReturnKind
     ADJ_ENCODING_MAX = 0x7f, // Maximum valid encoding in a byte
                              // Also used to mask off next bit from each encoding byte.
-    MORE_BYTES_TO_FOLLOW = 0x80 // If the High-bit of a header or adjustment byte 
+    MORE_BYTES_TO_FOLLOW = 0x80 // If the High-bit of a header or adjustment byte
                                // is set, then there are more adjustments to follow.
 };
 
@@ -416,7 +415,7 @@ enum infoHdrAdjust2 {
 
 #define INVALID_ARGTAB_OFFSET       0
 
-#include <pshpack1.h>
+#include "pshpack1.h"
 
 // Working set optimization: saving 12 * 128 = 1536 bytes in infoHdrShortcut
 struct InfoHdr;
@@ -524,7 +523,7 @@ union CallPattern {
     unsigned     val;
 };
 
-#include <poppack.h>
+#include "poppack.h"
 
 #define IH_MAX_PROLOG_SIZE (51)
 
@@ -543,8 +542,8 @@ inline void GetInfoHdr(int index, InfoHdr * header)
 
 PTR_CBYTE FASTCALL decodeHeader(PTR_CBYTE table, UINT32 version, InfoHdr* header);
 
-BYTE FASTCALL encodeHeaderFirst(const InfoHdr& header, InfoHdr* state, int* more, int *pCached);
-BYTE FASTCALL encodeHeaderNext(const InfoHdr& header, InfoHdr* state, BYTE &codeSet);
+uint8_t FASTCALL encodeHeaderFirst(const InfoHdr& header, InfoHdr* state, int* more, int *pCached);
+uint8_t FASTCALL encodeHeaderNext(const InfoHdr& header, InfoHdr* state, uint8_t &codeSet);
 
 size_t FASTCALL decodeUnsigned(PTR_CBYTE src, unsigned* value);
 size_t FASTCALL decodeUDelta(PTR_CBYTE src, unsigned* value, unsigned lastValue);
@@ -569,7 +568,7 @@ void FASTCALL decodeCallPattern(int         pattern,
     unsigned *  argMask,
     unsigned *  codeDelta);
 
-#endif // _TARGET_86_ 
+#endif // _TARGET_86_
 
 // Stack offsets must be 8-byte aligned, so we use this unaligned
 //  offset to represent that the method doesn't have a security object
diff --git a/src/Native/Runtime/gcdump.cpp b/src/Native/Runtime/gcdump.cpp
index 8b178f649..20eeae53c 100644
--- a/src/Native/Runtime/gcdump.cpp
+++ b/src/Native/Runtime/gcdump.cpp
@@ -301,10 +301,12 @@ void GCDump::DumpCallsiteString(UInt32 callsiteOffset, PTR_UInt8 pbCallsiteStrin
                 case CSR_NUM_RSI: regName = "RSI"; break;
                 case CSR_NUM_RDI: regName = "RDI"; break;
                 case CSR_NUM_RBP: regName = "RBP"; break;
+#ifdef _TARGET_AMD64_
                 case CSR_NUM_R12: regName = "R12"; break;
                 case CSR_NUM_R13: regName = "R13"; break;
                 case CSR_NUM_R14: regName = "R14"; break;
                 case CSR_NUM_R15: regName = "R15"; break;
+#endif // _TARGET_AMD64_
 #endif // _ARM_
                 }
                 gcPrintf("%02x          | 3  %s%s%s \n", b, regName, interior, pinned);
diff --git a/src/Native/Runtime/i386/AllocFast.S b/src/Native/Runtime/i386/AllocFast.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/AllocFast.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/CallDescrWorker.S b/src/Native/Runtime/i386/CallDescrWorker.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/CallDescrWorker.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/CallingConventionConverterHelpers.S b/src/Native/Runtime/i386/CallingConventionConverterHelpers.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/CallingConventionConverterHelpers.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/ExceptionHandling.S b/src/Native/Runtime/i386/ExceptionHandling.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/ExceptionHandling.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/Interlocked.S b/src/Native/Runtime/i386/Interlocked.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/Interlocked.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/InteropThunksHelpers.S b/src/Native/Runtime/i386/InteropThunksHelpers.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/InteropThunksHelpers.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/PInvoke.S b/src/Native/Runtime/i386/PInvoke.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/PInvoke.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/StubDispatch.S b/src/Native/Runtime/i386/StubDispatch.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/StubDispatch.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/UniversalTransition.S b/src/Native/Runtime/i386/UniversalTransition.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/UniversalTransition.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/i386/WriteBarriers.S b/src/Native/Runtime/i386/WriteBarriers.S
new file mode 100644
index 000000000..1dc275673
--- /dev/null
+++ b/src/Native/Runtime/i386/WriteBarriers.S
@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+// TODO: Implement
diff --git a/src/Native/Runtime/inc/gcinfo.h b/src/Native/Runtime/inc/gcinfo.h
index 5ce6b1c27..21e7a7ff0 100644
--- a/src/Native/Runtime/inc/gcinfo.h
+++ b/src/Native/Runtime/inc/gcinfo.h
@@ -361,10 +361,12 @@ enum CalleeSavedRegNum
     CSR_NUM_RSI = 0x01,
     CSR_NUM_RDI = 0x02,
     CSR_NUM_RBP = 0x03,
+#ifdef _TARGET_AMD64_
     CSR_NUM_R12 = 0x04,
     CSR_NUM_R13 = 0x05,
     CSR_NUM_R14 = 0x06,
     CSR_NUM_R15 = 0x07,
+#endif // _TARGET_AMD64_
 };
 
 enum CalleeSavedRegMask
@@ -393,10 +395,12 @@ enum ScratchRegNum
     SR_NUM_RAX = 0x00,
     SR_NUM_RCX = 0x01,
     SR_NUM_RDX = 0x02,
+#ifdef _TARGET_AMD64_
     SR_NUM_R8  = 0x03,
     SR_NUM_R9  = 0x04,
     SR_NUM_R10 = 0x05,
     SR_NUM_R11 = 0x06,
+#endif // _TARGET_AMD64_
 };
 
 enum ScratchRegMask
diff --git a/src/Native/Runtime/startup.cpp b/src/Native/Runtime/startup.cpp
index 2bc152cb1..4b2a7be4f 100644
--- a/src/Native/Runtime/startup.cpp
+++ b/src/Native/Runtime/startup.cpp
@@ -34,7 +34,7 @@ unsigned __int64 g_startupTimelineEvents[NUM_STARTUP_TIMELINE_EVENTS] = { 0 };
 #endif // PROFILE_STARTUP
 
 #ifdef PLATFORM_UNIX
-Int32 __stdcall RhpHardwareExceptionHandler(UIntNative faultCode, UIntNative faultAddress, PAL_LIMITED_CONTEXT* palContext, UIntNative* arg0Reg, UIntNative* arg1Reg);
+Int32 RhpHardwareExceptionHandler(UIntNative faultCode, UIntNative faultAddress, PAL_LIMITED_CONTEXT* palContext, UIntNative* arg0Reg, UIntNative* arg1Reg);
 #else
 Int32 __stdcall RhpVectoredExceptionHandler(PEXCEPTION_POINTERS pExPtrs);
 #endif
diff --git a/src/Native/Runtime/unix/UnixContext.cpp b/src/Native/Runtime/unix/UnixContext.cpp
index 495a33fcf..3be92658f 100644
--- a/src/Native/Runtime/unix/UnixContext.cpp
+++ b/src/Native/Runtime/unix/UnixContext.cpp
@@ -228,6 +228,7 @@ static void RegDisplayToUnwindContext(REGDISPLAY* regDisplay, unw_context_t *unw
 
 #undef ASSIGN_REG
 #undef ASSIGN_REG_PTR
+
 #endif // _ARM_
 }
 
@@ -325,6 +326,10 @@ static void GetContextPointer(unw_cursor_t *cursor, unw_context_t *unwContext, i
     GET_CONTEXT_POINTER(UNW_AARCH64_X26, 26)	\
     GET_CONTEXT_POINTER(UNW_AARCH64_X27, 27)	\
     GET_CONTEXT_POINTER(UNW_AARCH64_X28, 28)
+#elif defined(_X86_)
+#define GET_CONTEXT_POINTERS                    \
+    GET_CONTEXT_POINTER(UNW_X86_EBP, Rbp)       \
+    GET_CONTEXT_POINTER(UNW_X86_EBX, Rbx)
 #else
 #error unsupported architecture
 #endif
@@ -361,10 +366,23 @@ void UnwindCursorToRegDisplay(unw_cursor_t *cursor, unw_context_t *unwContext, R
     ASSIGN_REG(R14, R14)     \
     ASSIGN_REG(R15, R15)
 
-#define ASSIGN_TWO_ARGUMENT_REGS(arg0Reg, arg1Reg) \
-    MCREG_Rdi(nativeContext->uc_mcontext) = arg0Reg;      \
+#define ASSIGN_TWO_ARGUMENT_REGS(arg0Reg, arg1Reg)    \
+    MCREG_Rdi(nativeContext->uc_mcontext) = arg0Reg;  \
     MCREG_Rsi(nativeContext->uc_mcontext) = arg1Reg;
 
+#elif defined(_X86_)
+#define ASSIGN_CONTROL_REGS \
+    ASSIGN_REG(Eip, IP)     \
+    ASSIGN_REG(Esp, Rsp)
+
+#define ASSIGN_INTEGER_REGS  \
+    ASSIGN_REG(Ebx, Rbx)     \
+    ASSIGN_REG(Ebp, Rbp)
+
+#define ASSIGN_TWO_ARGUMENT_REGS(arg0Reg, arg1Reg)    \
+    MCREG_Ecx(nativeContext->uc_mcontext) = arg0Reg;  \
+    MCREG_Edx(nativeContext->uc_mcontext) = arg1Reg;
+
 #elif defined(_ARM_)
 
 #define ASSIGN_CONTROL_REGS  \
diff --git a/src/Native/gen-buildsys-clang.sh b/src/Native/gen-buildsys-clang.sh
index 72e9a0cbb..864f29172 100755
--- a/src/Native/gen-buildsys-clang.sh
+++ b/src/Native/gen-buildsys-clang.sh
@@ -127,6 +127,7 @@ else
         "-DCMAKE_OBJDUMP=$llvm_objdump" \
         "-DCMAKE_RANLIB=$llvm_ranlib" \
         "-DCMAKE_BUILD_TYPE=$build_type" \
+        "-DCLR_CMAKE_TARGET_ARCH=$build_arch" \
         $cmake_extra_defines \
         "$1/src/Native"
 fi
diff --git a/src/Native/inc/unix/poppack.h b/src/Native/inc/unix/poppack.h
new file mode 100644
index 000000000..aee3b49a3
--- /dev/null
+++ b/src/Native/inc/unix/poppack.h
@@ -0,0 +1,40 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+//
+
+//
+// ===========================================================================
+// File:  poppack.h
+//
+// ===========================================================================
+/*
+Abstract:
+
+    This file turns packing of structures off.  (That is, it enables
+    automatic alignment of structure fields.)  An include file is needed
+    because various compilers do this in different ways.
+
+    poppack.h is the complement to pshpack?.h.  An inclusion of poppack.h
+    MUST ALWAYS be preceded by an inclusion of one of pshpack?.h, in one-to-one
+    correspondence.
+
+    For Microsoft compatible compilers, this file uses the pop option
+    to the pack pragma so that it can restore the previous saved by the
+    pshpack?.h include file.
+
+*/
+
+#if ! (defined(lint) || defined(RC_INVOKED))
+#if ( _MSC_VER >= 800 && !defined(_M_I86)) || defined(_PUSHPOP_SUPPORTED)
+#pragma warning(disable:4103)
+#if !(defined( MIDL_PASS )) || defined( __midl )
+#pragma pack(pop)
+#else
+#pragma pack()
+#endif
+#else
+#pragma pack()
+#endif
+#endif // ! (defined(lint) || defined(RC_INVOKED))
+
diff --git a/src/Native/inc/unix/pshpack1.h b/src/Native/inc/unix/pshpack1.h
new file mode 100644
index 000000000..884e4c9c4
--- /dev/null
+++ b/src/Native/inc/unix/pshpack1.h
@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+//
+
+//
+// ===========================================================================
+// File: pshpack1.h
+//
+// ===========================================================================
+
+/*++
+
+Abstract:
+
+    This file turns 1 byte packing of structures on.  (That is, it disables
+    automatic alignment of structure fields.)  An include file is needed
+    because various compilers do this in different ways.  For Microsoft
+    compatible compilers, this files uses the push option to the pack pragma
+    so that the poppack.h include file can restore the previous packing
+    reliably.
+
+    The file poppack.h is the complement to this file.
+
+--*/
+
+#if ! (defined(lint) || defined(RC_INVOKED))
+#if ( _MSC_VER >= 800 && !defined(_M_I86)) || defined(_PUSHPOP_SUPPORTED)
+#pragma warning(disable:4103)
+#if !(defined( MIDL_PASS )) || defined( __midl )
+#pragma pack(push,1)
+#else
+#pragma pack(1)
+#endif
+#else
+#pragma pack(1)
+#endif
+#endif // ! (defined(lint) || defined(RC_INVOKED))
+
diff --git a/src/Native/inc/unix/pshpack4.h b/src/Native/inc/unix/pshpack4.h
new file mode 100644
index 000000000..c72dec96e
--- /dev/null
+++ b/src/Native/inc/unix/pshpack4.h
@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+//
+
+//
+// ===========================================================================
+// File: pshpack4.h
+//
+// ===========================================================================
+
+/*++
+
+Abstract:
+
+    This file turns 4 byte packing of structures on.  (That is, it disables
+    automatic alignment of structure fields.)  An include file is needed
+    because various compilers do this in different ways.  For Microsoft
+    compatible compilers, this files uses the push option to the pack pragma
+    so that the poppack.h include file can restore the previous packing
+    reliably.
+
+    The file poppack.h is the complement to this file.
+
+--*/
+
+#if ! (defined(lint) || defined(RC_INVOKED))
+#if ( _MSC_VER >= 800 && !defined(_M_I86)) || defined(_PUSHPOP_SUPPORTED)
+#pragma warning(disable:4103)
+#if !(defined( MIDL_PASS )) || defined( __midl )
+#pragma pack(push,4)
+#else
+#pragma pack(4)
+#endif
+#else
+#pragma pack(4)
+#endif
+#endif // ! (defined(lint) || defined(RC_INVOKED))
+
diff --git a/src/Native/libunwind/include/__libunwind_config.h b/src/Native/libunwind/include/__libunwind_config.h
index 93a3be1eb..df252b1fb 100644
--- a/src/Native/libunwind/include/__libunwind_config.h
+++ b/src/Native/libunwind/include/__libunwind_config.h
@@ -20,8 +20,8 @@
 #if defined(_LIBUNWIND_IS_NATIVE_ONLY)
 # if defined(__i386__)
 #  define _LIBUNWIND_TARGET_I386 1
-#  define _LIBUNWIND_CONTEXT_SIZE 25
-#  define _LIBUNWIND_CURSOR_SIZE 32
+#  define _LIBUNWIND_CONTEXT_SIZE 13
+#  define _LIBUNWIND_CURSOR_SIZE 23
 #  define _LIBUNWIND_HIGHEST_DWARF_REGISTER 9
 # elif defined(__x86_64__)
 #  define _LIBUNWIND_TARGET_X86_64 1