mips maltaup_xpa_defconfig build failure with clang

Hi All,

Not sure if it has been reported, mips maltaup_xpa_defconfig fails to build with clang with the error:

arch/mips/mm/tlbex.c:629:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context]

        if (cpu_has_rixi && !!_PAGE_NO_EXEC) {
                              ^
./arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC'
# define _PAGE_NO_EXEC          (1 << _PAGE_NO_EXEC_SHIFT)
                                   ^
arch/mips/mm/tlbex.c:2568:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context]
        if (!cpu_has_rixi || !_PAGE_NO_EXEC) {
                              ^
./arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC'
# define _PAGE_NO_EXEC          (1 << _PAGE_NO_EXEC_SHIFT)
                                   ^

--
Regards
Sudip

When CONFIG_XPA is enabled, Clang warns:

  arch/mips/mm/tlbex.c:629:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context]
          if (cpu_has_rixi && !!_PAGE_NO_EXEC) {
                              ^
  arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC'
  # define _PAGE_NO_EXEC          (1 << _PAGE_NO_EXEC_SHIFT)
                                     ^
  arch/mips/mm/tlbex.c:2568:24: error: converting the result of '<<' to a boolean; did you mean '(1 << _PAGE_NO_EXEC_SHIFT) != 0'? [-Werror,-Wint-in-bool-context]
          if (!cpu_has_rixi || !_PAGE_NO_EXEC) {
                                ^
  arch/mips/include/asm/pgtable-bits.h:174:28: note: expanded from macro '_PAGE_NO_EXEC'
  # define _PAGE_NO_EXEC          (1 << _PAGE_NO_EXEC_SHIFT)
                                     ^
  2 errors generated.

_PAGE_NO_EXEC can be '0' or '1 << _PAGE_NO_EXEC_SHIFT' depending on the build and runtime configuration, which is what the negation operators are trying to convey. To silence the warning, explicitly compare against 0 so the result of the '<<' operator is not implicitly converted to a boolean.

According to its documentation, GCC enables -Wint-in-bool-context with -Wall but this warning is not visible when building the same configuration with GCC. It appears GCC only warns when compiling C++, not C, although the documentation makes no note of this:
https://godbolt.org/z/x39q3brxf

---
 arch/mips/mm/tlbex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 8dbbd99fc7e8..be4d4670d649 100644
@@ -626,7 +626,7 @@ static __maybe_unused void build_convert_pte_to_entrylo(u32 **p,
 		return;
 	}
 
-	if (cpu_has_rixi && !!_PAGE_NO_EXEC) {
+	if (cpu_has_rixi && _PAGE_NO_EXEC != 0) {
 		if (fill_includes_sw_bits) {
 			UASM_i_ROTR(p, reg, reg, ilog2(_PAGE_GLOBAL));
 		} else {

@@ -2565,7 +2565,7 @@ static void check_pabits(void)
 	unsigned long entry;
 	unsigned pabits, fillbits;
 
-	if (!cpu_has_rixi || !_PAGE_NO_EXEC) {
+	if (!cpu_has_rixi || _PAGE_NO_EXEC == 0) {
 		/*
 		 * We'll only be making use of the fact that we can rotate bits
 		 * into the fill if the CPU supports RIXI, so don't bother

base-commit: 7d0d3fa7339ed5a06d6608b7cde9f079eba62bb1

2.37.1

applied to mips-next.

Thomas.

Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]