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| 1 | +========================================== |
| 2 | +How to build Windows Itanium applications. |
| 3 | +========================================== |
| 4 | + |
| 5 | +Introduction |
| 6 | +============ |
| 7 | + |
| 8 | +This document contains information describing how to create a Windows Itanium toolchain. |
| 9 | + |
| 10 | +Windows Itanium allows you to deploy Itanium C++ ABI applications on top of the MS VS CRT. |
| 11 | +This environment can use the Windows SDK headers directly and does not required additional |
| 12 | +headers or additional runtime machinery (such as is used by mingw). |
| 13 | + |
| 14 | +Windows Itanium Stack: |
| 15 | + |
| 16 | +* Uses the Itanium C++ abi. |
| 17 | +* libc++. |
| 18 | +* libc++-abi. |
| 19 | +* libunwind. |
| 20 | +* The MS VS CRT. |
| 21 | +* Is compatible with MS Windows SDK include headers. |
| 22 | +* COFF/PE file format. |
| 23 | +* LLD |
| 24 | + |
| 25 | +Note: compiler-rt is not used. This functionality is supplied by the MS VCRT. |
| 26 | + |
| 27 | +Prerequisites |
| 28 | +============= |
| 29 | + |
| 30 | +* The MS SDK is installed as part of MS Visual Studio. |
| 31 | +* Clang with support for the windows-itanium triple. |
| 32 | +* COFF LLD with support for the -autoimport switch. |
| 33 | + |
| 34 | +Known issues: |
| 35 | +============= |
| 36 | + |
| 37 | +SJLJ exceptions, "-fsjlj-exceptions", are the only currently supported model. |
| 38 | + |
| 39 | +link.exe (the MS linker) is unsuitable as it doesn't support auto-importing which |
| 40 | +is currently required to link correctly. However, if that limitation is removed |
| 41 | +then there are no other known issues with using link.exe. |
| 42 | + |
| 43 | +Currently, there is a lack of a usable Windows compiler driver for Windows Itanium. |
| 44 | +A reasonable work-around is to build clang with a windows-msvc default target and |
| 45 | +then override the triple with e.g. "-Xclang -triple -Xclang x86_64-unknown-windows-itanium". |
| 46 | +The linker can be specified with: "-fuse-ld=lld". |
| 47 | + |
| 48 | +In the Itanium C++ ABI the first member of an object is a pointer to the vtable |
| 49 | +for its class. The vtable is often emitted into the object file with the key function |
| 50 | +and must be imported for classes marked dllimport. The pointers must be globally |
| 51 | +unique. Unfortunately, the COFF/PE file format does not provide a mechanism to |
| 52 | +store a runtime address from another DLL into this pointer (although runtime |
| 53 | +addresses are patched into the IAT). Therefore, the compiler must emit some code, |
| 54 | +that runs after IAT patching but before anything that might use the vtable pointers, |
| 55 | +and sets the vtable pointer to the address from the IAT. For the special case of |
| 56 | +the references to vtables for __cxxabiv1::__class_type_info from typeinto objects |
| 57 | +there is no declaration available to the compiler so this can't be done. To allow |
| 58 | +programs to link we currently rely on the -auto-import switch in LLD to auto-import |
| 59 | +references to __cxxabiv1::__class_type_info pointers (see: https://reviews.llvm.org/D43184 |
| 60 | +for a related discussion). This allows for linking; but, code that actually uses |
| 61 | +such fields will not work as they these will not be fixed up at runtime. See |
| 62 | +_pei386_runtime_relocator which handles the runtime component of the autoimporting |
| 63 | +scheme used for mingw and comments in https://reviews.llvm.org/D43184 and |
| 64 | +https://reviews.llvm.org/D89518 for more. |
| 65 | + |
| 66 | +Assembling a Toolchain: |
| 67 | +======================= |
| 68 | + |
| 69 | +The procedure is: |
| 70 | + |
| 71 | +# Build an LLVM toolchain with support for Windows Itanium. |
| 72 | +# Use the toolchain from step 1. to build libc++, libc++abi, and libunwind. |
| 73 | + |
| 74 | +It is also possible to cross-compile from Linux. |
| 75 | + |
| 76 | +One method of building the libraries in step 2. is to build them "stand-alone". |
| 77 | +A stand-alone build doesn't involve the rest of the LLVM tree. The steps are: |
| 78 | + |
| 79 | +* ``cd build-dir`` |
| 80 | +* ``cmake -DLLVM_PATH=<path to llvm checkout e.g. /llvm-project/> -DCMAKE_INSTALL_PREFIX=<install path> <other options> <path to project e.g. /llvm-project/libcxxabi>`` |
| 81 | +* ``<make program e.g. ninja>`` |
| 82 | +* ``<make program> install`` |
| 83 | + |
| 84 | +More information on standalone builds can be found in the build documentation for |
| 85 | +the respective libraries. The next section discuss the salient options and modifications |
| 86 | +required for building and installing the libraries using standalone builds. This assumes |
| 87 | +that we are building libunwind and ibc++ as DLLs and statically linking libc++abi into |
| 88 | +libc++. Other build configurations are possible, but they are not discussed here. |
| 89 | + |
| 90 | +Common CMake configuration options: |
| 91 | +----------------------------------- |
| 92 | + |
| 93 | +* ``-D_LIBCPP_ABI_FORCE_ITANIUM'`` |
| 94 | + |
| 95 | +Tell the libc++ headers that the Itanium C++ ABI is being used. |
| 96 | + |
| 97 | +* ``-DCMAKE_C_FLAGS="-lmsvcrt -llegacy_stdio_definitions -D_NO_CRT_STDIO_INLINE"`` |
| 98 | + |
| 99 | +Supply CRT definitions including stdio definitions that have been removed from the MS VS CRT. |
| 100 | +We don't want the stdio functions decalred inline as they will casuse multiple defintiion |
| 101 | +errors when the same symbols are pulled in from legacy_stdio_definitions.ib. |
| 102 | + |
| 103 | +* ``-DCMAKE_INSTALL_PREFIX=<install path>`` |
| 104 | + |
| 105 | +Where to install the library and headers. |
| 106 | + |
| 107 | +Building libunwind: |
| 108 | +------------------- |
| 109 | + |
| 110 | +* ``-DLIBUNWIND_ENABLE_SHARED=ON`` |
| 111 | +* ``-DLIBUNWIND_ENABLE_STATIC=OFF`` |
| 112 | + |
| 113 | +libunwind can be built as a DLL. It is not dependent on other projects. |
| 114 | + |
| 115 | +* ``-DLIBUNWIND_USE_COMPILER_RT=OFF`` |
| 116 | + |
| 117 | +We use the MS runtime. |
| 118 | + |
| 119 | +The CMake files will need to be edited to prevent them adding GNU specific libraries to the link line. |
| 120 | + |
| 121 | +Building libc++abi: |
| 122 | +------------------ |
| 123 | + |
| 124 | +* ``-DLIBCXXABI_ENABLE_SHARED=OFF`` |
| 125 | +* ``-DLIBCXXABI_ENABLE_STATIC=ON`` |
| 126 | +* ``-DLIBCXX_ENABLE_SHARED=ON'`` |
| 127 | +* ``-DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON`` |
| 128 | + |
| 129 | +To break the symbol dependency between libc++abi and libc++ we |
| 130 | +build libc++abi as a static library and then statically link it |
| 131 | +into the libc++ DLL. This necessitates setting the CMake file |
| 132 | +to ensure that the visibility macros (which expand to dllexport/import) |
| 133 | +are expanded as they will be needed when creating the final libc++ |
| 134 | +DLL later, see: https://reviews.llvm.org/D90021. |
| 135 | + |
| 136 | +* ``-DLIBCXXABI_LIBCXX_INCLUDES=<path to libcxx>/include`` |
| 137 | + |
| 138 | +Where to find the libc++ headers |
| 139 | + |
| 140 | +Building libc++: |
| 141 | +---------------- |
| 142 | + |
| 143 | +* ``-DLIBCXX_ENABLE_SHARED=ON`` |
| 144 | +* ``-DLIBCXX_ENABLE_STATIC=OFF`` |
| 145 | + |
| 146 | +We build libc++ as a DLL and statically link libc++abi into it. |
| 147 | + |
| 148 | +* ``-DLIBCXX_INSTALL_HEADERS=ON`` |
| 149 | + |
| 150 | +Install the headers. |
| 151 | + |
| 152 | +* ``-DLIBCXX_USE_COMPILER_RT=OFF`` |
| 153 | + |
| 154 | +We use the MS runtime. |
| 155 | + |
| 156 | +* ``-DLIBCXX_HAS_WIN32_THREAD_API=ON`` |
| 157 | + |
| 158 | +Windows Itanium does not offer a POSIX-like layer over WIN32. |
| 159 | + |
| 160 | +* ``-DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON`` |
| 161 | +* ``-DLIBCXX_CXX_ABI=libcxxabi`` |
| 162 | +* ``-DLIBCXX_CXX_ABI_INCLUDE_PATHS=<libcxxabi src path>/include`` |
| 163 | +* ``-DLIBCXX_CXX_ABI_LIBRARY_PATH=<libcxxabi build path>/lib`` |
| 164 | + |
| 165 | +Use the static libc++abi library built earlier. |
| 166 | + |
| 167 | +* ``-DLIBCXX_NO_VCRUNTIME=ON`` |
| 168 | + |
| 169 | +Remove any dependency on the VC runtime - we need libc++abi to supply the C++ runtime. |
| 170 | + |
| 171 | +* ``-DCMAKE_C_FLAGS=<path to installed unwind.lib>`` |
| 172 | + |
| 173 | +As we are statically linking against libcxxabi we need to link |
| 174 | +against the unwind import library to resolve unwind references |
| 175 | +from the libcxxabi objects. |
| 176 | + |
| 177 | +* ``-DCMAKE_C_FLAGS+=' -UCLOCK_REALTIME'`` |
| 178 | + |
| 179 | +Prevent the inclusion of sys/time that MS doesn't provide. |
| 180 | + |
| 181 | +Notes: |
| 182 | +------ |
| 183 | + |
| 184 | +An example build recipe is available here: https://reviews.llvm.org/D88124 |
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