[PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

[PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

[Reiji Watanabe]

The id argument of ARM64_FTR_REG_OVERRIDE() is used for two purposes:
one as the system register encoding (used for the sys_id field of
__ftr_reg_entry), and the other as the register name (stringified
and used for the name field of arm64_ftr_reg), which is debug
information. The id argument is supposed to be a macro that
indicates an encoding of the register (eg. SYS_ID_AA64PFR0_EL1, etc).

ARM64_FTR_REG(), which also has the same id argument,
uses ARM64_FTR_REG_OVERRIDE() and passes the id to the macro.
Since the id argument is completely macro-expanded before it is
substituted into a macro body of ARM64_FTR_REG_OVERRIDE(),
the stringified id in the body of ARM64_FTR_REG_OVERRIDE is not
a human-readable register name, but a string of numeric bitwise
operations.

Fix this so that human-readable register names are available as
debug information.

Fixes: 8f266a5d878a ("arm64: cpufeature: Add global feature override facility")
Signed-off-by: Reiji Watanabe <reijiw@google.com>
---
 arch/arm64/kernel/cpufeature.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6ec7036ef7e1..7553c98f379f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -573,15 +573,19 @@ static const struct arm64_ftr_bits ftr_raz[] = {
 	ARM64_FTR_END,
 };
 
-#define ARM64_FTR_REG_OVERRIDE(id, table, ovr) {		\
+#define __ARM64_FTR_REG_OVERRIDE(id_str, id, table, ovr) {	\
 		.sys_id = id,					\
 		.reg = 	&(struct arm64_ftr_reg){		\
-			.name = #id,				\
+			.name = id_str,				\
 			.override = (ovr),			\
 			.ftr_bits = &((table)[0]),		\
 	}}
 
-#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)
+#define ARM64_FTR_REG_OVERRIDE(id, table, ovr)	\
+	__ARM64_FTR_REG_OVERRIDE(#id, id, table, ovr)
+
+#define ARM64_FTR_REG(id, table)		\
+	__ARM64_FTR_REG_OVERRIDE(#id, id, table, &no_override)
 
 struct arm64_ftr_override __ro_after_init id_aa64mmfr1_override;
 struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;
-- 
2.33.1.1089.g2158813163f-goog


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Re: [PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

[Marc Zyngier]

On Mon, 01 Nov 2021 04:54:21 +0000,
Reiji Watanabe <reijiw@google.com> wrote:
> 
> The id argument of ARM64_FTR_REG_OVERRIDE() is used for two purposes:
> one as the system register encoding (used for the sys_id field of
> __ftr_reg_entry), and the other as the register name (stringified
> and used for the name field of arm64_ftr_reg), which is debug
> information. The id argument is supposed to be a macro that
> indicates an encoding of the register (eg. SYS_ID_AA64PFR0_EL1, etc).
> 
> ARM64_FTR_REG(), which also has the same id argument,
> uses ARM64_FTR_REG_OVERRIDE() and passes the id to the macro.
> Since the id argument is completely macro-expanded before it is
> substituted into a macro body of ARM64_FTR_REG_OVERRIDE(),
> the stringified id in the body of ARM64_FTR_REG_OVERRIDE is not
> a human-readable register name, but a string of numeric bitwise
> operations.
> 
> Fix this so that human-readable register names are available as
> debug information.
> 
> Fixes: 8f266a5d878a ("arm64: cpufeature: Add global feature override facility")
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> ---
>  arch/arm64/kernel/cpufeature.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 6ec7036ef7e1..7553c98f379f 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -573,15 +573,19 @@ static const struct arm64_ftr_bits ftr_raz[] = {
>  	ARM64_FTR_END,
>  };
>  
> -#define ARM64_FTR_REG_OVERRIDE(id, table, ovr) {		\
> +#define __ARM64_FTR_REG_OVERRIDE(id_str, id, table, ovr) {	\
>  		.sys_id = id,					\
>  		.reg = 	&(struct arm64_ftr_reg){		\
> -			.name = #id,				\
> +			.name = id_str,				\
>  			.override = (ovr),			\
>  			.ftr_bits = &((table)[0]),		\
>  	}}
>  
> -#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)
> +#define ARM64_FTR_REG_OVERRIDE(id, table, ovr)	\
> +	__ARM64_FTR_REG_OVERRIDE(#id, id, table, ovr)
> +
> +#define ARM64_FTR_REG(id, table)		\
> +	__ARM64_FTR_REG_OVERRIDE(#id, id, table, &no_override)
>  
>  struct arm64_ftr_override __ro_after_init id_aa64mmfr1_override;
>  struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;


Seems reasonable to me.

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

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Re: [PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

[Oliver Upton]

On Sun, Oct 31, 2021 at 9:54 PM Reiji Watanabe <reijiw@google.com> wrote:
>
> The id argument of ARM64_FTR_REG_OVERRIDE() is used for two purposes:
> one as the system register encoding (used for the sys_id field of
> __ftr_reg_entry), and the other as the register name (stringified
> and used for the name field of arm64_ftr_reg), which is debug
> information. The id argument is supposed to be a macro that
> indicates an encoding of the register (eg. SYS_ID_AA64PFR0_EL1, etc).
>
> ARM64_FTR_REG(), which also has the same id argument,
> uses ARM64_FTR_REG_OVERRIDE() and passes the id to the macro.
> Since the id argument is completely macro-expanded before it is
> substituted into a macro body of ARM64_FTR_REG_OVERRIDE(),
> the stringified id in the body of ARM64_FTR_REG_OVERRIDE is not
> a human-readable register name, but a string of numeric bitwise
> operations.
>
> Fix this so that human-readable register names are available as
> debug information.
>
> Fixes: 8f266a5d878a ("arm64: cpufeature: Add global feature override facility")
> Signed-off-by: Reiji Watanabe <reijiw@google.com>

Reviewed-by: Oliver Upton <oupton@google.com>

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Re: [PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

[Will Deacon]

On Sun, 31 Oct 2021 21:54:21 -0700, Reiji Watanabe wrote:
> The id argument of ARM64_FTR_REG_OVERRIDE() is used for two purposes:
> one as the system register encoding (used for the sys_id field of
> __ftr_reg_entry), and the other as the register name (stringified
> and used for the name field of arm64_ftr_reg), which is debug
> information. The id argument is supposed to be a macro that
> indicates an encoding of the register (eg. SYS_ID_AA64PFR0_EL1, etc).
> 
> [...]

Applied to arm64 (for-next/core), thanks!

[1/1] arm64: arm64_ftr_reg->name may not be a human-readable string
      https://git.kernel.org/arm64/c/b0f364414a23

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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