linux-kernel - [PATCH] x86/csum: Fix clang -Wuninitialized in csum

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Message-Id: <20230526-csum_partial-wuninitialized-v1-1-ebc0108dcec1@kernel.org>
Date:   Fri, 26 May 2023 08:47:40 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     dave.hansen@...ux.intel.com, x86@...nel.org
Cc:     goldstein.w.n@...il.com, ndesaulniers@...gle.com, trix@...hat.com,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, kernel test robot <lkp@...el.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] x86/csum: Fix clang -Wuninitialized in csum_partial()

Clang warns:

  arch/x86/lib/csum-partial_64.c:74:20: error: variable 'result' is uninitialized when used here [-Werror,-Wuninitialized]
                  return csum_tail(result, temp64, odd);
                                   ^~~~~~
  arch/x86/lib/csum-partial_64.c:48:22: note: initialize the variable 'result' to silence this warning
          unsigned odd, result;
                              ^
                               = 0
  1 error generated.

The only initialization and uses of result in csum_partial() were moved
into csum_tail() but result is still being passed by value to
csum_tail() (clang's -Wuninitialized does not do interprocedural
analysis to realize that result is always assigned in csum_tail()
however). Sink the declaration of result into csum_tail() to clear up
the warning.

Fixes: 688eb8191b47 ("x86/csum: Improve performance of `csum_partial`")
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/202305262039.3HUYjWJk-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/x86/lib/csum-partial_64.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
index fe5861951b15..cea25ca8b8cf 100644
--- a/arch/x86/lib/csum-partial_64.c
+++ b/arch/x86/lib/csum-partial_64.c
@@ -21,8 +21,10 @@ static inline unsigned short from32to16(unsigned a)
 	return b;
 }
 
-static inline __wsum csum_tail(unsigned int result, u64 temp64, int odd)
+static inline __wsum csum_tail(u64 temp64, int odd)
 {
+	unsigned int result;
+
 	result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
 	if (unlikely(odd)) {
 		result = from32to16(result);
@@ -45,7 +47,7 @@ static inline __wsum csum_tail(unsigned int result, u64 temp64, int odd)
 __wsum csum_partial(const void *buff, int len, __wsum sum)
 {
 	u64 temp64 = (__force u64)sum;
-	unsigned odd, result;
+	unsigned odd;
 
 	odd = 1 & (unsigned long) buff;
 	if (unlikely(odd)) {
@@ -71,7 +73,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
 		    "adcq $0,%[res]"
 		    : [res] "+r"(temp64)
 		    : [src] "r"(buff), "m"(*(const char(*)[40])buff));
-		return csum_tail(result, temp64, odd);
+		return csum_tail(temp64, odd);
 	}
 	if (unlikely(len >= 64)) {
 		/*
@@ -141,7 +143,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
 		    : [res] "+r"(temp64)
 		    : [trail] "r"(trail));
 	}
-	return csum_tail(result, temp64, odd);
+	return csum_tail(temp64, odd);
 }
 EXPORT_SYMBOL(csum_partial);
 

---
base-commit: 688eb8191b475db5acfd48634600b04fd3dda9ad
change-id: 20230526-csum_partial-wuninitialized-08aa3d492f07

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