linux-kernel - [PATCH v3 1/1] x86/cpu: Make sure flag_is_changeable

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Message-ID: <20240910084356.1518209-1-andriy.shevchenko@linux.intel.com>
Date: Tue, 10 Sep 2024 11:42:42 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Cc: Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Dave Hansen <dave.hansen@...el.com>
Subject: [PATCH v3 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

When flag_is_changeable_p() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y:

arch/x86/kernel/cpu/common.c:351:19: error: unused function 'flag_is_changeable_p' [-Werror,-Wunused-function]
  351 | static inline int flag_is_changeable_p(u32 flag)
      |                   ^~~~~~~~~~~~~~~~~~~~

Fix this by moving core around to make sure flag_is_changeable_p() is
always being used.

See also commit 6863f5643dd7 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

Suggested-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---

v3: rewritten as suggested (Dave)
v2: marked both 32- and 64-bit cases

 arch/x86/kernel/cpu/common.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d4e539d4e158..5525afa6e888 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -275,22 +275,14 @@ static int __init x86_noinvpcid_setup(char *s)
 }
 early_param("noinvpcid", x86_noinvpcid_setup);
 
-#ifdef CONFIG_X86_32
-static int cachesize_override = -1;
-static int disable_x86_serial_nr = 1;
-
-static int __init cachesize_setup(char *str)
-{
-	get_option(&str, &cachesize_override);
-	return 1;
-}
-__setup("cachesize=", cachesize_setup);
-
 /* Standard macro to see if a specific flag is changeable */
 static inline int flag_is_changeable_p(u32 flag)
 {
 	u32 f1, f2;
 
+	if (!IS_ENABLED(CONFIG_X86_32))
+		return 1;
+
 	/*
 	 * Cyrix and IDT cpus allow disabling of CPUID
 	 * so the code below may return different results
@@ -315,6 +307,17 @@ static inline int flag_is_changeable_p(u32 flag)
 	return ((f1^f2) & flag) != 0;
 }
 
+#ifdef CONFIG_X86_32
+static int cachesize_override = -1;
+static int disable_x86_serial_nr = 1;
+
+static int __init cachesize_setup(char *str)
+{
+	get_option(&str, &cachesize_override);
+	return 1;
+}
+__setup("cachesize=", cachesize_setup);
+
 /* Probe for the CPUID instruction */
 int have_cpuid_p(void)
 {
@@ -348,10 +351,6 @@ static int __init x86_serial_nr_setup(char *s)
 }
 __setup("serialnumber", x86_serial_nr_setup);
 #else
-static inline int flag_is_changeable_p(u32 flag)
-{
-	return 1;
-}
 static inline void squash_the_stupid_serial_number(struct cpuinfo_x86 *c)
 {
 }
@@ -1087,7 +1086,6 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 {
-#ifdef CONFIG_X86_32
 	int i;
 
 	/*
@@ -1108,7 +1106,6 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 				break;
 			}
 		}
-#endif
 }
 
 #define NO_SPECULATION		BIT(0)
-- 
2.43.0.rc1.1336.g36b5255a03ac