while compile arch/arm64/include/asm/cpufeature.h with
-Werror=type-limits enabled, errors shown as below:
./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule':
./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) &&
^~
./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule':
./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) &&
^~
Modify the return judgment statement, use
"((val - min) < (val - max - 1))" to confirm that returns
true in “min <= val <= max” cases, false in other cases.
Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values")
Signed-off-by: Lin Yujun <[email protected]>
---
arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 03d1c9d7af82..0a6bda025141 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -54,6 +54,9 @@ enum ftr_type {
#define FTR_VISIBLE_IF_IS_ENABLED(config) \
(IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
+#define IN_RANGE_INCLUSIVE(val, min, max) \
+ (((val) - (min)) < ((val) - (max) - 1))
+
struct arm64_ftr_bits {
bool sign; /* Value is signed ? */
bool visible;
@@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void)
val = cpuid_feature_extract_unsigned_field(mmfr0,
ID_AA64MMFR0_EL1_TGRAN4_SHIFT);
- return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) &&
- (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
+ return IN_RANGE_INCLUSIVE(val,
+ ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN,
+ ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
}
static inline bool system_supports_64kb_granule(void)
@@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void)
val = cpuid_feature_extract_unsigned_field(mmfr0,
ID_AA64MMFR0_EL1_TGRAN64_SHIFT);
- return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) &&
- (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
+ return IN_RANGE_INCLUSIVE(val,
+ ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN,
+ ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
}
static inline bool system_supports_16kb_granule(void)
@@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void)
val = cpuid_feature_extract_unsigned_field(mmfr0,
ID_AA64MMFR0_EL1_TGRAN16_SHIFT);
- return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) &&
- (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
+ return IN_RANGE_INCLUSIVE(val,
+ ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN,
+ ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
}
static inline bool system_supports_mixed_endian_el0(void)
--
2.34.1
On Tue, Feb 21, 2023 at 09:27:40AM +0800, Lin Yujun wrote:
> while compile arch/arm64/include/asm/cpufeature.h with
> -Werror=type-limits enabled, errors shown as below:
>
> ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule':
> ./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
> return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) &&
> ^~
> ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule':
> ./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
> return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) &&
> ^~
When is the `-Werror=type-limits` flag enabled by the build system?
We have patterns like this all over the kernel, and I don't think this is
indicative of a real problem, and I don't think that we need to change code to
make this warning disappear.
> Modify the return judgment statement, use
> "((val - min) < (val - max - 1))" to confirm that returns
> true in “min <= val <= max” cases, false in other cases.
That expression is far less clear than the existing code, so I do not think
that is a good idea.
> Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values")
What functional error does this fix?
What configuration is broken?
Thanks,
Mark.
> Signed-off-by: Lin Yujun <[email protected]>
> ---
> arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 03d1c9d7af82..0a6bda025141 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -54,6 +54,9 @@ enum ftr_type {
> #define FTR_VISIBLE_IF_IS_ENABLED(config) \
> (IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
>
> +#define IN_RANGE_INCLUSIVE(val, min, max) \
> + (((val) - (min)) < ((val) - (max) - 1))
> +
> struct arm64_ftr_bits {
> bool sign; /* Value is signed ? */
> bool visible;
> @@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void)
> val = cpuid_feature_extract_unsigned_field(mmfr0,
> ID_AA64MMFR0_EL1_TGRAN4_SHIFT);
>
> - return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) &&
> - (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
> + return IN_RANGE_INCLUSIVE(val,
> + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN,
> + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
> }
>
> static inline bool system_supports_64kb_granule(void)
> @@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void)
> val = cpuid_feature_extract_unsigned_field(mmfr0,
> ID_AA64MMFR0_EL1_TGRAN64_SHIFT);
>
> - return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) &&
> - (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
> + return IN_RANGE_INCLUSIVE(val,
> + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN,
> + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
> }
>
> static inline bool system_supports_16kb_granule(void)
> @@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void)
> val = cpuid_feature_extract_unsigned_field(mmfr0,
> ID_AA64MMFR0_EL1_TGRAN16_SHIFT);
>
> - return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) &&
> - (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
> + return IN_RANGE_INCLUSIVE(val,
> + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN,
> + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
> }
>
> static inline bool system_supports_mixed_endian_el0(void)
> --
> 2.34.1
>
On Tue, 21 Feb 2023 at 11:37, Mark Rutland <[email protected]> wrote:
>
> On Tue, Feb 21, 2023 at 09:27:40AM +0800, Lin Yujun wrote:
> > while compile arch/arm64/include/asm/cpufeature.h with
> > -Werror=type-limits enabled, errors shown as below:
> >
> > ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule':
> > ./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
> > return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) &&
> > ^~
> > ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule':
> > ./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
> > return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) &&
> > ^~
The usefulness of this diagnostic is debatable even when the right
hand is a literal '0' but warning about symbolic constants like this
is actively evil.
In general, preprocessor #defined values can depend on Kconfig
settings or other build configuration switches, and this warning
encourages us to remove the expression altogether, which could mean
introducing a bug if the macro may assume values >0 in other
configurations.
Ergo, we must ignore -Wtype-limits until it is fixed, and can at least
distinguish literal 0 constants from ones instantiated by a CPP macro.
>
> When is the `-Werror=type-limits` flag enabled by the build system?
>
> We have patterns like this all over the kernel, and I don't think this is
> indicative of a real problem, and I don't think that we need to change code to
> make this warning disappear.
>
> > Modify the return judgment statement, use
> > "((val - min) < (val - max - 1))" to confirm that returns
> > true in “min <= val <= max” cases, false in other cases.
>
> That expression is far less clear than the existing code, so I do not think
> that is a good idea.
>
> > Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values")
>
> What functional error does this fix?
>
> What configuration is broken?
>
> Thanks,
> Mark.
>
> > Signed-off-by: Lin Yujun <[email protected]>
> > ---
> > arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------
> > 1 file changed, 12 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> > index 03d1c9d7af82..0a6bda025141 100644
> > --- a/arch/arm64/include/asm/cpufeature.h
> > +++ b/arch/arm64/include/asm/cpufeature.h
> > @@ -54,6 +54,9 @@ enum ftr_type {
> > #define FTR_VISIBLE_IF_IS_ENABLED(config) \
> > (IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
> >
> > +#define IN_RANGE_INCLUSIVE(val, min, max) \
> > + (((val) - (min)) < ((val) - (max) - 1))
> > +
> > struct arm64_ftr_bits {
> > bool sign; /* Value is signed ? */
> > bool visible;
> > @@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void)
> > val = cpuid_feature_extract_unsigned_field(mmfr0,
> > ID_AA64MMFR0_EL1_TGRAN4_SHIFT);
> >
> > - return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) &&
> > - (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
> > + return IN_RANGE_INCLUSIVE(val,
> > + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN,
> > + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
> > }
> >
> > static inline bool system_supports_64kb_granule(void)
> > @@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void)
> > val = cpuid_feature_extract_unsigned_field(mmfr0,
> > ID_AA64MMFR0_EL1_TGRAN64_SHIFT);
> >
> > - return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) &&
> > - (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
> > + return IN_RANGE_INCLUSIVE(val,
> > + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN,
> > + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
> > }
> >
> > static inline bool system_supports_16kb_granule(void)
> > @@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void)
> > val = cpuid_feature_extract_unsigned_field(mmfr0,
> > ID_AA64MMFR0_EL1_TGRAN16_SHIFT);
> >
> > - return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) &&
> > - (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
> > + return IN_RANGE_INCLUSIVE(val,
> > + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN,
> > + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
> > }
> >
> > static inline bool system_supports_mixed_endian_el0(void)
> > --
> > 2.34.1
> >
Thanks for your advice
在 2023/2/21 23:10, Ard Biesheuvel 写道:
> On Tue, 21 Feb 2023 at 11:37, Mark Rutland <[email protected]> wrote:
>> On Tue, Feb 21, 2023 at 09:27:40AM +0800, Lin Yujun wrote:
>>> while compile arch/arm64/include/asm/cpufeature.h with
>>> -Werror=type-limits enabled, errors shown as below:
>>>
>>> ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_4kb_granule':
>>> ./arch/arm64/include/asm/cpufeature.h:653:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
>>> return (val >= ID_AA64MMFR0_TGRAN4_SUPPORTED_MIN) &&
>>> ^~
>>> ./arch/arm64/include/asm/cpufeature.h: In function 'system_supports_64kb_granule':
>>> ./arch/arm64/include/asm/cpufeature.h:666:14: error: comparison of unsigned expression >= 0 is always true [-Werror=type-limits]
>>> return (val >= ID_AA64MMFR0_TGRAN64_SUPPORTED_MIN) &&
>>> ^~
> The usefulness of this diagnostic is debatable even when the right
> hand is a literal '0' but warning about symbolic constants like this
> is actively evil.
>
> In general, preprocessor #defined values can depend on Kconfig
> settings or other build configuration switches, and this warning
> encourages us to remove the expression altogether, which could mean
> introducing a bug if the macro may assume values >0 in other
> configurations.
>
> Ergo, we must ignore -Wtype-limits until it is fixed, and can at least
> distinguish literal 0 constants from ones instantiated by a CPP macro.
>
>
>> When is the `-Werror=type-limits` flag enabled by the build system?
>>
>> We have patterns like this all over the kernel, and I don't think this is
>> indicative of a real problem, and I don't think that we need to change code to
>> make this warning disappear.
>>
>>> Modify the return judgment statement, use
>>> "((val - min) < (val - max - 1))" to confirm that returns
>>> true in “min <= val <= max” cases, false in other cases.
>> That expression is far less clear than the existing code, so I do not think
>> that is a good idea.
>>
>>> Fixes: 79d82cbcbb3d ("arm64/kexec: Test page size support with new TGRAN range values")
>> What functional error does this fix?
>>
>> What configuration is broken?
>>
>> Thanks,
>> Mark.
>>
>>> Signed-off-by: Lin Yujun <[email protected]>
>>> ---
>>> arch/arm64/include/asm/cpufeature.h | 18 ++++++++++++------
>>> 1 file changed, 12 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
>>> index 03d1c9d7af82..0a6bda025141 100644
>>> --- a/arch/arm64/include/asm/cpufeature.h
>>> +++ b/arch/arm64/include/asm/cpufeature.h
>>> @@ -54,6 +54,9 @@ enum ftr_type {
>>> #define FTR_VISIBLE_IF_IS_ENABLED(config) \
>>> (IS_ENABLED(config) ? FTR_VISIBLE : FTR_HIDDEN)
>>>
>>> +#define IN_RANGE_INCLUSIVE(val, min, max) \
>>> + (((val) - (min)) < ((val) - (max) - 1))
>>> +
>>> struct arm64_ftr_bits {
>>> bool sign; /* Value is signed ? */
>>> bool visible;
>>> @@ -693,8 +696,9 @@ static inline bool system_supports_4kb_granule(void)
>>> val = cpuid_feature_extract_unsigned_field(mmfr0,
>>> ID_AA64MMFR0_EL1_TGRAN4_SHIFT);
>>>
>>> - return (val >= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN) &&
>>> - (val <= ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
>>> + return IN_RANGE_INCLUSIVE(val,
>>> + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MIN,
>>> + ID_AA64MMFR0_EL1_TGRAN4_SUPPORTED_MAX);
>>> }
>>>
>>> static inline bool system_supports_64kb_granule(void)
>>> @@ -706,8 +710,9 @@ static inline bool system_supports_64kb_granule(void)
>>> val = cpuid_feature_extract_unsigned_field(mmfr0,
>>> ID_AA64MMFR0_EL1_TGRAN64_SHIFT);
>>>
>>> - return (val >= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN) &&
>>> - (val <= ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
>>> + return IN_RANGE_INCLUSIVE(val,
>>> + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MIN,
>>> + ID_AA64MMFR0_EL1_TGRAN64_SUPPORTED_MAX);
>>> }
>>>
>>> static inline bool system_supports_16kb_granule(void)
>>> @@ -719,8 +724,9 @@ static inline bool system_supports_16kb_granule(void)
>>> val = cpuid_feature_extract_unsigned_field(mmfr0,
>>> ID_AA64MMFR0_EL1_TGRAN16_SHIFT);
>>>
>>> - return (val >= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN) &&
>>> - (val <= ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
>>> + return IN_RANGE_INCLUSIVE(val,
>>> + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MIN,
>>> + ID_AA64MMFR0_EL1_TGRAN16_SUPPORTED_MAX);
>>> }
>>>
>>> static inline bool system_supports_mixed_endian_el0(void)
>>> --
>>> 2.34.1
>>>
> .