[libunwind] Add a cmake option for disabling the use of the dynamic linker

[mstorsjo]

Summary

On windows, the psapi function for querying the dynamic linker for loaded modules (EnumProcessModules) are unavailable when targeting the UWP/"Windows Store" api subsets.

Such a build relies on the static frame registration functions for finding exception handlers.

[rnk]

lgtm

[mstorsjo]

I choose not to commit this one after all, I managed to work around the issue with Windows Store apps in a much simpler way by providing a Windows Store compatible version of EnumProcessModules, see https://sourceforge.net/p/mingw-w64/mingw-w64/ci/0e1f41358845706a1adafcf4f9d27db0319dd3d9/.

CMakeLists.txt

 option(LIBUNWIND_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBUNWIND_ENABLE_SHARED "Build libunwind as a shared library." ON)
 option(LIBUNWIND_ENABLE_STATIC "Build libunwind as a static library." ON)
 option(LIBUNWIND_ENABLE_CROSS_UNWINDING "Enable cross-platform unwinding support." OFF)
 option(LIBUNWIND_ENABLE_ARM_WMMX "Enable unwinding support for ARM WMMX registers." OFF)
 option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 option(LIBUNWIND_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
 option(LIBUNWIND_INCLUDE_DOCS "Build the libunwind documentation." ${LLVM_INCLUDE_DOCS})
+option(LIBUNWIND_ENABLE_DYNAMIC_LINKER "Query the dynamic linker for finding exception frames." ON)
 
 set(LIBUNWIND_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBUNWIND_INSTALL_LIBRARY "Install the libunwind library." ON)
 set(LIBUNWIND_TARGET_TRIPLE "" CACHE STRING "Target triple for cross compiling.")
 set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
 set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
 set(LIBUNWIND_TEST_LINKER_FLAGS "" CACHE STRING

 if (LIBUNWIND_ENABLE_ARM_WMMX)
   # __ARM_WMMX is a compiler pre-define (as per the ACLE 2.0). Clang does not
   # define this macro for any supported target at present. Therefore, here we
   # provide the option to explicitly enable support for WMMX registers in the
   # unwinder.
   list(APPEND LIBUNWIND_COMPILE_FLAGS -D__ARM_WMMX)
 endif()
 
+# Ability to disable the use of the dynamic linker
+if (NOT LIBUNWIND_ENABLE_DYNAMIC_LINKER)
+  list(APPEND LIBUNWIND_COMPILE_FLAGS -D_LIBUNWIND_DISABLE_DYNAMIC_LINKER)
+endif()
+
 # This is the _ONLY_ place where add_definitions is called.
 if (MSVC)
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
 endif()
 
 # Disable DLL annotations on Windows for static builds.
 if (WIN32 AND LIBUNWIND_ENABLE_STATIC AND NOT LIBUNWIND_ENABLE_SHARED)
   add_definitions(-D_LIBUNWIND_DISABLE_VISIBILITY_ANNOTATIONS)

src/AddressSpace.hpp

LocalAddressSpace::getEncodedP(pint_t &addr, pint_t end, uint8_t encoding,
   if (encoding & DW_EH_PE_indirect)
     result = getP(result);
 
   return result;
 }
 
 inline bool LocalAddressSpace::findUnwindSections(pint_t targetAddr,
                                                   UnwindInfoSections &info) {
-#ifdef __APPLE__
-  dyld_unwind_sections dyldInfo;
-  if (_dyld_find_unwind_sections((void *)targetAddr, &dyldInfo)) {
-    info.dso_base                      = (uintptr_t)dyldInfo.mh;
- #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
-    info.dwarf_section                 = (uintptr_t)dyldInfo.dwarf_section;
-    info.dwarf_section_length          = dyldInfo.dwarf_section_length;
- #endif
-    info.compact_unwind_section        = (uintptr_t)dyldInfo.compact_unwind_section;
-    info.compact_unwind_section_length = dyldInfo.compact_unwind_section_length;
-    return true;
-  }
-#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL)
+#if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_IS_BAREMETAL)
   // Bare metal is statically linked, so no need to ask the dynamic loader
   info.dwarf_section_length = (uintptr_t)(&__eh_frame_end - &__eh_frame_start);
   info.dwarf_section =        (uintptr_t)(&__eh_frame_start);
   _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: section %p length %p",
                              (void *)info.dwarf_section, (void *)info.dwarf_section_length);
 #if defined(_LIBUNWIND_SUPPORT_DWARF_INDEX)
   info.dwarf_index_section =        (uintptr_t)(&__eh_frame_hdr_start);
   info.dwarf_index_section_length = (uintptr_t)(&__eh_frame_hdr_end - &__eh_frame_hdr_start);
   _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: index section %p length %p",
                              (void *)info.dwarf_index_section, (void *)info.dwarf_index_section_length);
 #endif
   if (info.dwarf_section_length)
     return true;
 #elif defined(_LIBUNWIND_ARM_EHABI) && defined(_LIBUNWIND_IS_BAREMETAL)
   // Bare metal is statically linked, so no need to ask the dynamic loader
   info.arm_section =        (uintptr_t)(&__exidx_start);
   info.arm_section_length = (uintptr_t)(&__exidx_end - &__exidx_start);
   _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: section %p length %p",
                              (void *)info.arm_section, (void *)info.arm_section_length);
   if (info.arm_section && info.arm_section_length)
     return true;
+#elif !defined(_LIBUNWIND_DISABLE_DYNAMIC_LINKER)
+#ifdef __APPLE__
+  dyld_unwind_sections dyldInfo;
+  if (_dyld_find_unwind_sections((void *)targetAddr, &dyldInfo)) {
+    info.dso_base                      = (uintptr_t)dyldInfo.mh;
+ #if defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND)
+    info.dwarf_section                 = (uintptr_t)dyldInfo.dwarf_section;
+    info.dwarf_section_length          = dyldInfo.dwarf_section_length;
+ #endif
+    info.compact_unwind_section        = (uintptr_t)dyldInfo.compact_unwind_section;
+    info.compact_unwind_section_length = dyldInfo.compact_unwind_section_length;
+    return true;
+  }
 #elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_WIN32)
   HMODULE mods[1024];
   HANDLE process = GetCurrentProcess();
   DWORD needed;
 
   if (!EnumProcessModules(process, mods, sizeof(mods), &needed))
     return false;
 
#else // defined(_LIBUNWIND_ARM_EHABI)
           }
         }
         return found_obj && found_hdr;
  #endif
       },
       &cb_data);
   return static_cast<bool>(found);
 #endif
+#endif // !_LIBUNWIND_DISABLE_DYNAMIC_LINKER
 
   return false;
 }
 
 
 inline bool LocalAddressSpace::findOtherFDE(pint_t targetAddr, pint_t &fde) {
 #ifdef __APPLE__
   return checkKeyMgrRegisteredFDEs(targetAddr, *((void**)&fde));