2024-02-15 13:56:48

by Geert Uytterhoeven

Subject: [PATCH v2] ARM: ptrace: Use bitfield helpers

The isa_mode() macro extracts two fields, and recombines them into a
single value.

Make this more obvious by using the FIELD_GET() helper, and shifting the
result into its final resting place.

Signed-off-by: Geert Uytterhoeven <[email protected]>
---
No changes in generated assembler code.

v2:
- Drop irrelevant comment about non-existing off-by-one error,
- Remove unnecessary parens.
---
arch/arm/include/asm/ptrace.h | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 7f44e88d1f25bcc5..14a38cc67e0bc966 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -10,6 +10,7 @@
#include <uapi/asm/ptrace.h>

#ifndef __ASSEMBLY__
+#include <linux/bitfield.h>
#include <linux/types.h>

struct pt_regs {
@@ -35,8 +36,8 @@ struct svc_pt_regs {

#ifndef CONFIG_CPU_V7M
#define isa_mode(regs) \
- ((((regs)->ARM_cpsr & PSR_J_BIT) >> (__ffs(PSR_J_BIT) - 1)) | \
- (((regs)->ARM_cpsr & PSR_T_BIT) >> (__ffs(PSR_T_BIT))))
+ (FIELD_GET(PSR_J_BIT, (regs)->ARM_cpsr) << 1 | \
+ FIELD_GET(PSR_T_BIT, (regs)->ARM_cpsr))
#else
#define isa_mode(regs) 1 /* Thumb */
#endif
--
2.34.1

2024-02-15 17:51:56

by Oleg Nesterov

Subject: Re: [PATCH v2] ARM: ptrace: Use bitfield helpers

Sorry for the noise, can't resist...

I am replying only because I wasn't aware of bitfield.h and useful
helpers there.

Thank you ;)

On 02/15, Geert Uytterhoeven wrote:
>
> #ifndef __ASSEMBLY__
> +#include <linux/bitfield.h>
> #include <linux/types.h>
>
> struct pt_regs {
> @@ -35,8 +36,8 @@ struct svc_pt_regs {
>
> #ifndef CONFIG_CPU_V7M
> #define isa_mode(regs) \
> - ((((regs)->ARM_cpsr & PSR_J_BIT) >> (__ffs(PSR_J_BIT) - 1)) | \
> - (((regs)->ARM_cpsr & PSR_T_BIT) >> (__ffs(PSR_T_BIT))))
> + (FIELD_GET(PSR_J_BIT, (regs)->ARM_cpsr) << 1 | \
> + FIELD_GET(PSR_T_BIT, (regs)->ARM_cpsr))

Reviewed-by: Oleg Nesterov <[email protected]>