-Wuninitialized in arch/mips/include/asm/syscall.h

[nathanchance]

In file included from arch/mips/kernel/ptrace.c:45:
arch/mips/include/asm/syscall.h:130:3: warning: variable 'ret' is uninitialized when used here [-Wuninitialized]
                ret |= mips_get_syscall_arg(args++, task, regs, i++);
                ^~~
arch/mips/include/asm/syscall.h:123:9: note: initialize the variable 'ret' to silence this warning
        int ret;
               ^
                = 0
1 warning generated.

Tentative patch (going to send as a series):

From dbe84f9fe5a2e82ba23b143e1a2cf5be895c8fe2 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <natechancellor@gmail.com>
Date: Wed, 17 Jul 2019 11:42:56 -0700
Subject: [PATCH] MIPS/ptrace: Update mips_get_syscall_arg's return type

clang warns:

In file included from arch/mips/kernel/ptrace.c:45:
arch/mips/include/asm/syscall.h:130:3: warning: variable 'ret' is
uninitialized when used here [-Wuninitialized]
                ret |= mips_get_syscall_arg(args++, task, regs, i++);
                ^~~
arch/mips/include/asm/syscall.h:123:9: note: initialize the variable
'ret' to silence this warning
        int ret;
               ^
                = 0
1 warning generated.

It's not wrong; however, it's not an issue in practice because ret is
only assigned to, not read from. ret could just be initialized to zero
but looking into it further, ret has been unused since it was first
added in 2012 so just get rid of it and update mips_get_syscall_arg's
return type since none of the return values are ever checked. If it is
ever needed again, this commit can be reverted and ret can be properly
initialized.

Fixes: c0ff3c53d4f9 ("MIPS: Enable HAVE_ARCH_TRACEHOOK.")
Link: https://github.com/ClangBuiltLinux/linux/issues/604
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/mips/include/asm/syscall.h | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index 83bb439597d8..06f01390b7f2 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -54,7 +54,7 @@ static inline void mips_syscall_update_nr(struct task_struct *task,
 		task_thread_info(task)->syscall = regs->regs[2];
 }
 
-static inline unsigned long mips_get_syscall_arg(unsigned long *arg,
+static inline void mips_get_syscall_arg(unsigned long *arg,
 	struct task_struct *task, struct pt_regs *regs, unsigned int n)
 {
 	unsigned long usp __maybe_unused = regs->regs[29];
@@ -63,23 +63,25 @@ static inline unsigned long mips_get_syscall_arg(unsigned long *arg,
 	case 0: case 1: case 2: case 3:
 		*arg = regs->regs[4 + n];
 
-		return 0;
+		return;
 
 #ifdef CONFIG_32BIT
 	case 4: case 5: case 6: case 7:
-		return get_user(*arg, (int *)usp + n);
+		get_user(*arg, (int *)usp + n);
+		return;
 #endif
 
 #ifdef CONFIG_64BIT
 	case 4: case 5: case 6: case 7:
 #ifdef CONFIG_MIPS32_O32
 		if (test_tsk_thread_flag(task, TIF_32BIT_REGS))
-			return get_user(*arg, (int *)usp + n);
+			get_user(*arg, (int *)usp + n);
+			return
 		else
 #endif
 			*arg = regs->regs[4 + n];
 
-		return 0;
+		return;
 #endif
 
 	default:
@@ -126,21 +128,13 @@ static inline void syscall_get_arguments(struct task_struct *task,
 {
 	unsigned int i = 0;
 	unsigned int n = 6;
-	int ret;
 
 	/* O32 ABI syscall() */
 	if (mips_syscall_is_indirect(task, regs))
 		i++;
 
 	while (n--)
-		ret |= mips_get_syscall_arg(args++, task, regs, i++);
-
-	/*
-	 * No way to communicate an error because this is a void function.
-	 */
-#if 0
-	return ret;
-#endif
+		mips_get_syscall_arg(args++, task, regs, i++);
 }
 
 extern const unsigned long sys_call_table[];
-- 
2.22.0

[nathanchance]

Patch sent: https://lore.kernel.org/lkml/20190812033120.43013-3-natechancellor@gmail.com/

[nathanchance]

Patch accepted: https://git.kernel.org/mips/c/077ff3be06e8de2657075dd2738b9a21f8ebd890

[nathanchance]

Merged into mainline: https://git.kernel.org/linus/077ff3be06e8de2657075dd2738b9a21f8ebd890