Fix C file generation in jit.bcsave.

Thanks to codicodi.

(cherry picked from commit 62903ba)

LuaJIT allows exporting bytecode to a C file using the option `-b`, see
[1]. For building a generated C file in C++ projects, C file uses a
macro `__cplusplus` [2], but this macro was broken by the commit
a9dd47b ("Extend -b to generate
c/h/obj/o files with embedded bytecode."). With this breakage, C/C++
compiler removes the definition of an array with the bytecode, and the
resulted object file misses a symbol with the bytecode.

The patch fixes the broken macro.

Note, test test/lua-Harness-tests/411-luajit.t checks the presence of
the macro `__cplusplus` in the generated C file, however, it doesn't
catch the bug.

Sergey Bronnikov:
* added the description and the test for the problem

Part of tarantool/tarantool#9145

1. https://luajit.org/running.html
2. https://en.cppreference.com/w/cpp/preprocessor/replace

Author: Mike Pall

src/jit/bcsave.lua

@@ -133,7 +133,7 @@ local function bcsave_c(ctx, output, s)
   local fp = savefile(output, "w")
   if ctx.type == "c" then
     fp:write(format([[
-#ifdef _cplusplus
+#ifdef __cplusplus
 extern "C"
 #endif
 #ifdef _WIN32

test/tarantool-tests/CMakeLists.txt

@@ -38,6 +38,7 @@ add_subdirectory(gh-6098-fix-side-exit-patching-on-arm64)
 add_subdirectory(gh-6189-cur_L)
 add_subdirectory(lj-416-xor-before-jcc)
 add_subdirectory(lj-549-bytecode-loader)
+add_subdirectory(lj-551-bytecode-c-broken-macro)
 add_subdirectory(lj-601-fix-gc-finderrfunc)
 add_subdirectory(lj-727-lightuserdata-itern)
 add_subdirectory(lj-802-panic-at-mcode-protfail)

test/tarantool-tests/lj-551-bytecode-c-broken-macro.test.lua

@@ -0,0 +1,22 @@
+local tap = require('tap')
+local test = tap.test('lj-551-bytecode-c-broken-macro'):skipcond({
+  -- XXX: Tarantool doesn't use default LuaJIT loaders, and Lua
+  -- bytecode can't be loaded from the shared library. For more
+  -- info: https://github.com/tarantool/tarantool/issues/9671.
+  -- luacheck: no global
+  ['Test uses exotic type of loaders (see #9671)'] = _TARANTOOL,
+})
+
+test:plan(4)
+
+local function check_module(t, module_name)
+  local ok, module = pcall(require, module_name)
+  local message = ('symbol %q is available in a library'):format(module_name)
+  t:ok(ok, message)
+  t:is(module.msg, 'Lango team')
+end
+
+check_module(test, 'script_c')
+check_module(test, 'script_cc')
+
+test:done(true)

test/tarantool-tests/lj-551-bytecode-c-broken-macro/CMakeLists.txt

@@ -0,0 +1,35 @@
+enable_language(CXX)
+
+set(LUA_FILE ${CMAKE_CURRENT_SOURCE_DIR}/script.lua)
+
+make_lua_path(LUA_PATH
+  PATHS
+    ${LUAJIT_SOURCE_DIR}/?.lua
+    ${LUAJIT_SOURCE_DIR}/jit/?.lua
+)
+
+macro(BuildTestBCLib file_ext)
+  set(LIB_NAME "script_${file_ext}")
+  set(LUA_SOURCE ${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}.lua)
+  set(EXT_SOURCE ${CMAKE_CURRENT_BINARY_DIR}/${LIB_NAME}.${file_ext})
+
+  # XXX: Module has to be copied, since bytecode dumper uses its
+  # name within the exported symbol.
+  add_custom_target(export_bc_${file_ext}
+    COMMAND ${CMAKE_COMMAND} -E copy ${LUA_FILE} ${LUA_SOURCE}
+    COMMAND ${CMAKE_COMMAND} -E env
+      LUA_PATH=${LUA_PATH} ${LUAJIT_TEST_BINARY} -b ${LUA_SOURCE} ${EXT_SOURCE}
+    COMMAND ${CMAKE_COMMAND} -E remove ${LUA_SOURCE}
+    DEPENDS ${LUAJIT_TEST_BINARY} ${LUA_FILE}
+    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    BYPRODUCTS ${EXT_SOURCE}
+    COMMENT "Exporting bytecode to a ${file_ext} file"
+    VERBATIM
+  )
+
+  BuildTestCLib(${LIB_NAME} ${EXT_SOURCE})
+  add_dependencies(${LIB_NAME} export_bc_${file_ext})
+endmacro()
+
+BuildTestBCLib("c")
+BuildTestBCLib("cc")

test/tarantool-tests/lj-551-bytecode-c-broken-macro/script.lua

@@ -0,0 +1,3 @@
+return {
+  msg = 'Lango team',
+}