Assert non-executable stack for assembly files

Some GNU linkers do not set the stack as non-executable when the
`.note.GNU-stack` section is missing. Herein, we fix this.

Also remove some warnings when compiling assembly on Clang by removing
unneccessary/unused compiler options.

Also remove some warnings in source code.

Makefile.in

@@ -91,8 +91,8 @@ LIBS2:=-lflint $(LIBS)
 PIC_FLAG:=@PIC_FLAG@
 
 ifeq ($(WANT_ASSEMBLY),1)
-ASM_OBJ_FLAGS:=$(filter-out -D%,$(CPPFLAGS) $(LIB_CPPFLAGS)) $(filter-out -funroll-loops -pedantic, $(CFLAGS))
-ASM_LOBJ_FLAGS:=$(filter-out -D%,$(PIC_FLAG)) $(ASM_OBJ_FLAGS)
+ASMFLAGS:=@ASMFLAGS@
+ASM_PIC_FLAG:=$(filter-out -D%,$(PIC_FLAG))
 endif
 
 UNROLL_LOOPS:=@UNROLL_LOOPS@
@@ -580,7 +580,7 @@ endef
 ifeq ($(WANT_ASSEMBLY),1)
 %.o: %.s
 	@echo "  CC  $(<:$(BUILD_DIR)/%.s=%.asm)"
-	@$(CC) $(ASM_OBJ_FLAGS) -c $< -o $@
+	@$(CC) $(ASMFLAGS) -c $< -o $@
 endif
 
 $(foreach dir, $(DIRS), $(eval $(call xxx_OBJS_rule,$(dir))))
@@ -600,7 +600,7 @@ endef
 ifeq ($(WANT_ASSEMBLY),1)
 %.lo: %_pic.s
 	@echo "  CC  $(<:$(BUILD_DIR)/%.s=%.asm)"
-	@$(CC) $(ASM_LOBJ_FLAGS) -c $< -o $@
+	@$(CC) $(ASMFLAGS) $(ASM_PIC_FLAG) -c $< -o $@
 endif
 
 $(foreach dir, $(DIRS), $(eval $(call xxx_LOBJS_rule,$(dir))))

acinclude.m4

@@ -101,23 +101,45 @@ define(FAST_VROUNDPD_PATTERN,
 [[znver[2-4]* | sandybridge* | ivybridge*]])
 
 
-dnl  FLINT_CLANG([action-if-true],[action-if-false])
+dnl  FLINT_CC_IS_GCC([action-if-true],[action-if-false])
+dnl  -----------------------
+dnl  Checks if compiler is GCC.
+
+AC_DEFUN([FLINT_CC_IS_GCC],
+[AC_CACHE_CHECK([if compiler is GCC],
+                flint_cv_cc_is_gcc,
+[flint_cv_cc_is_gcc="no"
+AC_PREPROC_IFELSE([AC_LANG_PROGRAM([
+#if !(defined(__GNUC__) && !defined(__clang__))
+#error
+error
+#endif
+],[])],
+[flint_cv_cc_is_gcc="yes"])
+])
+AS_VAR_IF([flint_cv_cc_is_gcc],"yes",
+    [m4_default([$1], :)],
+    [m4_default([$2], :)])
+])
+
+
+dnl  FLINT_CC_IS_CLANG([action-if-true],[action-if-false])
 dnl  -----------------------
 dnl  Checks if compiler is clang.
 
-AC_DEFUN([FLINT_CLANG],
+AC_DEFUN([FLINT_CC_IS_CLANG],
 [AC_CACHE_CHECK([if compiler is Clang],
-                flint_cv_clang,
-[flint_cv_clang="no"
+                flint_cv_cc_is_clang,
+[flint_cv_cc_is_clang="no"
 AC_PREPROC_IFELSE([AC_LANG_PROGRAM([
 #ifndef __clang__
 #error
 error
 #endif
 ],[])],
-[flint_cv_clang="yes"])
+[flint_cv_cc_is_clang="yes"])
 ])
-AS_VAR_IF([flint_cv_clang],"yes",
+AS_VAR_IF([flint_cv_cc_is_clang],"yes",
     [m4_default([$1], :)],
     [m4_default([$2], :)])
 ])
@@ -695,6 +717,43 @@ rm -f conftest*
 ])
 
 
+dnl  CL_ASM_NOEXECSTACK
+dnl  -------------------
+dnl
+dnl  Checks whether the stack can be marked nonexecutable by passing an option
+dnl  to the C-compiler when acting on .s files. Appends that option to ASMFLAGS.
+dnl  This macro is adapted from one found in GLIBC-2.3.5.
+dnl
+dnl  FIXME: This test looks broken. It tests that a file with
+dnl  .note.GNU-stack... can be compiled/assembled with -Wa,--noexecstack.  It
+dnl  does not determine if that command-line option has any effect on general
+dnl  asm code.
+AC_DEFUN([CL_ASM_NOEXECSTACK],
+[AC_REQUIRE([AC_PROG_CC])
+AC_CACHE_CHECK([whether assembler supports --noexecstack option],
+                cl_cv_asm_noexecstack,
+[dnl
+  cat > conftest.c <<EOF
+void foo() {}
+EOF
+  if AC_TRY_COMMAND([${CC} $CFLAGS $CPPFLAGS
+                     -S -o conftest.s conftest.c >/dev/null]) \
+     && grep .note.GNU-stack conftest.s >/dev/null \
+     && AC_TRY_COMMAND([${CC} $CFLAGS $CPPFLAGS -Wa,--noexecstack
+                       -c -o conftest.o conftest.s >/dev/null])
+  then
+    cl_cv_asm_noexecstack=yes
+  else
+    cl_cv_asm_noexecstack=no
+  fi
+  rm -f conftest*])
+  if test "$cl_cv_asm_noexecstack" = yes; then
+    ASMFLAGS="$ASMFLAGS -Wa,--noexecstack"
+  fi
+  AC_SUBST(ASMFLAGS)
+])
+
+
 dnl  GMP_ASM_LABEL_SUFFIX
 dnl  --------------------
 dnl  : - is usual.

configure.ac

@@ -827,6 +827,9 @@ dnl AC_PROG_CC
 
 AC_PROG_MKDIR_P
 
+FLINT_CC_IS_GCC
+FLINT_CC_IS_CLANG
+
 ################################################################################
 # environment variables
 ################################################################################
@@ -1178,9 +1181,12 @@ AC_CHECK_FUNCS([aligned_alloc _aligned_malloc])
 # CFLAGS
 ################################################################################
 
-# The following is needed for Clang to check for unknown options.
-FLINT_CLANG([AX_CHECK_COMPILE_FLAG([-Werror=unknown-warning-option],
-                                   [CFLAGS="-Werror=unknown-warning-option"])])
+if test "$flint_cv_cc_is_clang" = "yes";
+then
+    # The following is needed for Clang to check for unknown options.
+    AX_CHECK_COMPILE_FLAG([-Werror=unknown-warning-option],
+                          [CFLAGS="-Werror=unknown-warning-option"])
+fi
 
 if test "$enable_coverage" = "yes";
 then
@@ -1322,6 +1328,7 @@ then
     GMP_PROG_M4
     GMP_PATH_NM
 
+    CL_ASM_NOEXECSTACK
     GMP_ASM_TEXT
     GMP_ASM_DATA
     GMP_ASM_LABEL_SUFFIX

src/machine_vectors.h

@@ -477,7 +477,7 @@ FLINT_FORCE_INLINE vec4n CAT6(vec4n, permute, i0, i1, i2, i3)(vec4n a) { \
 DEFINE_IT(3,2,1,0)
 #undef DEFINE_IT
 
-FLINT_FORCE_INLINE vec4n vec4n_zero()
+FLINT_FORCE_INLINE vec4n vec4n_zero(void)
 {
     return _mm256_setzero_si256();
 }

src/mpn_extras/get_str.c

@@ -23,4 +23,4 @@ _flint_mpn_get_str(mp_srcptr x, mp_size_t n)
     s = fmpz_get_str(NULL, 10, t);
     fmpz_clear(t);
     return s;
-}
+}