More targeted suppression of bogus GCC -Werror=stringop-overflow=

...given that <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87296#c5>
"[8/9/10/11 Regression] -Wstringop-overflow false positive due to using MEM_REF
type of &MEM" is declared fixed now on GCC 11 trunk.

(Moving -Wno-stringop-overflow from gb_CFLAGS_WERROR to gb_CXXFLAGS_COMMON is
done for no other reason than to harmonize this with the code for the similar
HAVE_BROKEN_GCC_WMAYBE_UNINITIALIZED.)

Change-Id: I3468138c9bbda28f754d4162cb9c059796bd3932
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/111029
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

3 files changed, 54 insertions, 3 deletions

diff --git a/config_host.mk.in b/config_host.mk.in
index fb64c61e66f7..c6c9b7eae351 100644
--- a/config_host.mk.in
+++ b/config_host.mk.in
@@ -259,6 +259,7 @@ export GTK3_LIBS=$(gb_SPACE)@GTK3_LIBS@
 export USING_X11=@USING_X11@
 export HAMCREST_JAR=@HAMCREST_JAR@
 export HAVE_BROKEN_GCC_WMAYBE_UNINITIALIZED=@HAVE_BROKEN_GCC_WMAYBE_UNINITIALIZED@
+export HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW=@HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW@
 export HAVE_CLANG_DEBUG_INFO_KIND_CONSTRUCTOR=@HAVE_CLANG_DEBUG_INFO_KIND_CONSTRUCTOR@
 export HAVE_GCC_AVX=@HAVE_GCC_AVX@
 export HAVE_GCC_BUILTIN_ATOMIC=@HAVE_GCC_BUILTIN_ATOMIC@
diff --git a/configure.ac b/configure.ac
index 78bb7998e62c..c3e15f6397de 100644
--- a/configure.ac
+++ b/configure.ac
@@ -7343,6 +7343,55 @@ if test "$GCC" = yes && test "$COM_IS_CLANG" != TRUE; then
 fi
 AC_SUBST([HAVE_BROKEN_GCC_WMAYBE_UNINITIALIZED])
 
+dnl Check for <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87296#c5> "[8/9/10/11 Regression]
+dnl -Wstringop-overflow false positive due to using MEM_REF type of &MEM" (fixed in GCC 11), which
+dnl hits us e.g. with GCC 10 and --enable-optimized at
+dnl
+dnl   In file included from include/rtl/string.hxx:49,
+dnl                    from include/rtl/ustring.hxx:43,
+dnl                    from include/osl/file.hxx:35,
+dnl                    from include/codemaker/global.hxx:28,
+dnl                    from include/codemaker/options.hxx:23,
+dnl                    from codemaker/source/commoncpp/commoncpp.cxx:24:
+dnl   In function ‘char* rtl::addDataHelper(char*, const char*, std::size_t)’,
+dnl       inlined from ‘static char* rtl::ToStringHelper<const char [N]>::addData(char*, const char*) [with long unsigned int N = 3]’ at include/rtl/stringconcat.hxx:147:85,
+dnl       inlined from ‘char* rtl::OStringConcat<T1, T2>::addData(char*) const [with T1 = const char [3]; T2 = rtl::OString]’ at include/rtl/stringconcat.hxx:226:103,
+dnl       inlined from ‘rtl::OStringBuffer& rtl::OStringBuffer::append(rtl::OStringConcat<T1, T2>&&) [with T1 = const char [3]; T2 = rtl::OString]’ at include/rtl/strbuf.hxx:599:30,
+dnl       inlined from ‘rtl::OString codemaker::cpp::scopedCppName(const rtl::OString&, bool)’ at codemaker/source/commoncpp/commoncpp.cxx:53:55:
+dnl   include/rtl/stringconcat.hxx:78:15: error: writing 2 bytes into a region of size 1 [-Werror=stringop-overflow=]
+dnl      78 |         memcpy( buffer, data, length );
+dnl         |         ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
+HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW=
+if test "$GCC" = yes && test "$COM_IS_CLANG" != TRUE; then
+    AC_MSG_CHECKING([whether $CXX_BASE might report false -Werror=stringop-overflow=])
+    AC_LANG_PUSH([C++])
+    save_CXXFLAGS=$CXXFLAGS
+    CXXFLAGS="$CXXFLAGS $CXXFLAGS_CXX11 -Werror -Wstringop-overflow"
+    if test "$ENABLE_OPTIMIZED" = TRUE; then
+        CXXFLAGS="$CXXFLAGS -O2"
+    else
+        CXXFLAGS="$CXXFLAGS -O0"
+    fi
+    dnl Test code taken from <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87296#c0>:
+    AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+            void fill(char const * begin, char const * end, char c);
+            struct q {
+                char ids[4];
+                char username[6];
+            };
+            void test(q & c) {
+                fill(c.ids, c.ids + sizeof(c.ids), '\0');
+                __builtin_strncpy(c.username, "root", sizeof(c.username));
+            }
+        ]])], [AC_MSG_RESULT([no])], [
+            HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW=TRUE
+            AC_MSG_RESULT([yes])
+        ])
+    CXXFLAGS=$save_CXXFLAGS
+    AC_LANG_POP([C++])
+fi
+AC_SUBST([HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW])
+
 dnl ===================================================================
 dnl CPU Intrinsics support - SSE, AVX
 dnl ===================================================================
diff --git a/solenv/gbuild/platform/com_GCC_defs.mk b/solenv/gbuild/platform/com_GCC_defs.mk
index 047f121106de..d8784dfb6a6e 100644
--- a/solenv/gbuild/platform/com_GCC_defs.mk
+++ b/solenv/gbuild/platform/com_GCC_defs.mk
@@ -93,6 +93,10 @@ ifeq ($(HAVE_BROKEN_GCC_WMAYBE_UNINITIALIZED),TRUE)
 gb_CXXFLAGS_COMMON += -Wno-maybe-uninitialized
 endif
 
+ifeq ($(HAVE_BROKEN_GCC_WSTRINGOP_OVERFLOW),TRUE)
+gb_CXXFLAGS_COMMON += -Wno-stringop-overflow
+endif
+
 gb_CXXFLAGS_Wundef = -Wno-undef
 
 ifeq ($(strip $(gb_GCOV)),YES)
@@ -158,9 +162,6 @@ endif
 endif
 
 gb_CFLAGS_WERROR = $(if $(ENABLE_WERROR),-Werror)
-ifeq ($(ENABLE_OPTIMIZED)-$(COM_IS_CLANG),TRUE-)
-gb_CFLAGS_WERROR += -Wno-stringop-overflow
-endif
 
 # This is the default in non-C++11 mode
 ifeq ($(COM_IS_CLANG),TRUE)