test: fix LuaJIT-tests for old libc version

The `strtod parsing` subtest in the <lib/base/tonumber_scan.lua> checks
the results yielded by the `strtod()` via FFI call. In versions before
2.19 it returns an incorrect result for "0x1p-2075" [1]. This patch
skips this test for a smaller version of the libc installed.

[1]: https://sourceware.org/bugzilla/show_bug.cgi?id=16151

test/CMakeLists.txt

@@ -73,6 +73,7 @@ separate_arguments(LUAJIT_TEST_COMMAND)
 
 set(CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 include(AddTestLib)
+include(GetLibCVersion)
 include(LibRealPath)
 
 # CTEST_FLAGS is used by CMake targets in test suites.

test/LuaJIT-tests/CMakeLists.txt

@@ -62,6 +62,15 @@ if(CMAKE_C_FLAGS MATCHES "-march=skylake-avx512")
   list(APPEND LUAJIT_TEST_TAGS_EXTRA +avx512)
 endif()
 
+if(NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+  GetLibCVersion(LIBC_VERSION)
+  # XXX: <tonumber_scan.lua> uses `strtod()`, old versions of
+  # which have the bug [1] for "0x1p-2075" parsing. Add the skip
+  # check for it.
+  # [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=16151
+  list(APPEND LUAJIT_TEST_TAGS_EXTRA +libc=${LIBC_VERSION})
+endif()
+
 set(TEST_SUITE_NAME "LuaJIT-tests")
 
 # XXX: The call produces both test and target <LuaJIT-tests-deps>

test/LuaJIT-tests/lib/base/tonumber_scan.lua

@@ -186,7 +186,9 @@ do --- tonumber parsing
   test_conv(tonumber)
 end
 
-do --- strtod parsing
+-- Skip for the old libc version with the bug in the `strtod()`.
+-- See also https://sourceware.org/bugzilla/show_bug.cgi?id=16151.
+do --- strtod parsing -libc<2.19
   test_conv(function(s)
     local d = ffi.C.strtod(s, e)
     return (e[0][0] == 0 and #s ~= 0) and d or nil

test/cmake/GetLibCVersion.cmake

@@ -0,0 +1,35 @@
+# Get the libc version installed in the system.
+# XXX: uses `LibRealPath`, so unsupported for OSX.
+macro(GetLibCVersion output)
+  LibRealPath(libcpath "libc.so.6")
+
+  # Get the version from the library name.
+  if(libcpath MATCHES "libc-([0-9]+\.[0-9]+)\.so")
+    set(${output} ${CMAKE_MATCH_1})
+  else()
+    # Try to directly run the library and parse the version from
+    # the output message.
+    execute_process(
+      COMMAND ${libcpath}
+      OUTPUT_VARIABLE LIB_C_INFO
+      ERROR_VARIABLE ERROR_MSG
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      RESULT_VARIABLE RES
+    )
+
+    if(NOT RES EQUAL 0)
+      message(FATAL_ERROR "Executing '${libcpath}' has failed: '${ERROR_MSG}'")
+    endif()
+
+    if(LIB_C_INFO MATCHES "^.*stable release version ([0-9]+\.[0-9]+)")
+      set(${output} ${CMAKE_MATCH_1})
+    else()
+      message(FATAL_ERROR "Can't determine libc version")
+    endif()
+
+    unset(RES)
+    unset(ERROR_MSG)
+    unset(LIB_C_INFO)
+  endif()
+  unset(CMAKE_MATCH_1)
+endmacro()