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From:   Nathan Chancellor <nathan@kernel.org>
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        torvalds@linux-foundation.org, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        Nathan Chancellor <nathan@kernel.org>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Subject: [PATCH] MIPS: tlbex: Explicitly compare _PAGE_NO_EXEC against 0
Date:   Tue,  2 Aug 2022 10:59:36 -0700
Message-Id: <20220802175936.2278362-1-nathan@kernel.org>
In-Reply-To: <YulSY1pDms0ZyNs9@debian>
References: <YulSY1pDms0ZyNs9@debian>
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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

Reported-by: Sudip Mukherjee (Codethink) <sudipm.mukherjee@gmail.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/mips/mm/tlbex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
index 8dbbd99fc7e8..be4d4670d649 100644
--- a/arch/mips/mm/tlbex.c
+++ b/arch/mips/mm/tlbex.c
@@ -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