linux-kernel - [PATCH fixes] riscv: uaccess: Fix -Wuninitialized and -Wshadow in __put_user

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Message-Id: <20250715-riscv-uaccess-fix-self-init-val-v1-1-82b8e911f120@kernel.org>
Date: Tue, 15 Jul 2025 20:07:01 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>
Cc: Clément Léger <cleger@...osinc.com>, 
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH fixes] riscv: uaccess: Fix -Wuninitialized and -Wshadow in
 __put_user_nocheck

After a recent change in clang to strengthen uninitialized warnings [1],
there is a warning from val being uninitialized in __put_user_nocheck
when called from futex_put_value():

  kernel/futex/futex.h:326:18: warning: variable 'val' is uninitialized when used within its own initialization [-Wuninitialized]
    326 |         unsafe_put_user(val, to, Efault);
        |         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
  arch/riscv/include/asm/uaccess.h:464:21: note: expanded from macro 'unsafe_put_user'
    464 |         __put_user_nocheck(x, (ptr), label)
        |         ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~
  arch/riscv/include/asm/uaccess.h:314:36: note: expanded from macro '__put_user_nocheck'
    314 |                 __inttype(x) val = (__inttype(x))x;                     \
        |                              ~~~                 ^

While not on by default, -Wshadow flags the same mistake:

  kernel/futex/futex.h:326:2: warning: declaration shadows a local variable [-Wshadow]
    326 |         unsafe_put_user(val, to, Efault);
        |         ^
  arch/riscv/include/asm/uaccess.h:464:2: note: expanded from macro 'unsafe_put_user'
    464 |         __put_user_nocheck(x, (ptr), label)
        |         ^
  arch/riscv/include/asm/uaccess.h:314:16: note: expanded from macro '__put_user_nocheck'
    314 |                 __inttype(x) val = (__inttype(x))x;                     \
        |                              ^
  kernel/futex/futex.h:320:48: note: previous declaration is here
    320 | static __always_inline int futex_put_value(u32 val, u32 __user *to)
        |                                                ^

Use a three underscore prefix for the val variable in __put_user_nocheck
to avoid clashing with either val or __val, which are both used within
the put_user macros, clearing up all warnings.

Closes: https://github.com/ClangBuiltLinux/linux/issues/2109
Fixes: ca1a66cdd685 ("riscv: uaccess: do not do misaligned accesses in get/put_user()")
Link: https://github.com/llvm/llvm-project/commit/2464313eef01c5b1edf0eccf57a32cdee01472c7 [1]
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
It would be good if this could make 6.16 final. Otherwise, consider
adding a 'Cc: stable@...r.kernel.org' during application.
---
 arch/riscv/include/asm/uaccess.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index 525e50db24f7..b88a6218b7f2 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -311,8 +311,8 @@ do {								\
 do {								\
 	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) &&	\
 	    !IS_ALIGNED((uintptr_t)__gu_ptr, sizeof(*__gu_ptr))) {	\
-		__inttype(x) val = (__inttype(x))x;			\
-		if (__asm_copy_to_user_sum_enabled(__gu_ptr, &(val), sizeof(*__gu_ptr))) \
+		__inttype(x) ___val = (__inttype(x))x;			\
+		if (__asm_copy_to_user_sum_enabled(__gu_ptr, &(___val), sizeof(*__gu_ptr))) \
 			goto label;				\
 		break;						\
 	}							\

---
base-commit: 5903a7452e642f1475f274373633522db168b60b
change-id: 20250715-riscv-uaccess-fix-self-init-val-ed44574d380e

Best regards,
--  
Nathan Chancellor <nathan@...nel.org>