[PATCH v4 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

[PATCH v4 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

[Andy Shevchenko]

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").

While at it, fix the argument type to be unsigned long, although it currently
only runs in 32-bit cases.

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

v4: fixed the type of parameter (hpa)
v3: rewritten as suggested (Dave)
v2: marked both 32- and 64-bit cases

 arch/x86/kernel/cpu/common.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a5f221ea5688..49682e35f9bd 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -276,22 +276,14 @@ 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)
+static inline int flag_is_changeable_p(unsigned long 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
@@ -316,6 +308,17 @@ 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)
 {
@@ -349,10 +352,6 @@ 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)
 {
 }
@@ -1088,7 +1087,6 @@ 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;
 
 	/*
@@ -1109,7 +1107,6 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 				break;
 			}
 		}
-#endif
 }
 
 #define NO_SPECULATION		BIT(0)
-- 
2.43.0.rc1.1336.g36b5255a03ac

Re: [PATCH v4 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

[H. Peter Anvin]

On November 8, 2024 3:11:46 PM GMT+01:00, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
>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").
>
>While at it, fix the argument type to be unsigned long, although it currently
>only runs in 32-bit cases.
>
>Suggested-by: Dave Hansen <dave.hansen@intel.com>
>Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>---
>
>v4: fixed the type of parameter (hpa)
>v3: rewritten as suggested (Dave)
>v2: marked both 32- and 64-bit cases
>
> arch/x86/kernel/cpu/common.c | 33 +++++++++++++++------------------
> 1 file changed, 15 insertions(+), 18 deletions(-)
>
>diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
>index a5f221ea5688..49682e35f9bd 100644
>--- a/arch/x86/kernel/cpu/common.c
>+++ b/arch/x86/kernel/cpu/common.c
>@@ -276,22 +276,14 @@ 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)
>+static inline int flag_is_changeable_p(unsigned long 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
>@@ -316,6 +308,17 @@ 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)
> {
>@@ -349,10 +352,6 @@ 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)
> {
> }
>@@ -1088,7 +1087,6 @@ 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;
> 
> 	/*
>@@ -1109,7 +1107,6 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
> 				break;
> 			}
> 		}
>-#endif
> }
> 
> #define NO_SPECULATION		BIT(0)

It's good that you are changing the return type, but we need to be consistent and change f1, f2 to match. At the same time, I suggest changing the return type to bool.

Re: [PATCH v4 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

[Andy Shevchenko]

On Fri, Nov 08, 2024 at 04:13:05PM +0100, H. Peter Anvin wrote:
> On November 8, 2024 3:11:46 PM GMT+01:00, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> >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").
> >
> >While at it, fix the argument type to be unsigned long, although it currently
> >only runs in 32-bit cases.

...

> It's good that you are changing the return type, but we need to be consistent
> and change f1, f2 to match. At the same time, I suggest changing the return
> type to bool.

Ah, that makes sense!

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v4 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

[Andy Shevchenko]

On Fri, Nov 08, 2024 at 05:18:27PM +0200, Andy Shevchenko wrote:
> On Fri, Nov 08, 2024 at 04:13:05PM +0100, H. Peter Anvin wrote:
> > On November 8, 2024 3:11:46 PM GMT+01:00, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > >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").
> > >
> > >While at it, fix the argument type to be unsigned long, although it currently
> > >only runs in 32-bit cases.

...

> > It's good that you are changing the return type, but we need to be consistent
> > and change f1, f2 to match. At the same time, I suggest changing the return
> > type to bool.
> 
> Ah, that makes sense!

All addressed in v5:
20241108153105.1578186-1-andriy.shevchenko@linux.intel.com
You are in Cc there.

-- 
With Best Regards,
Andy Shevchenko