[PATCH v2 1/5] powerpc/64: use 32-bit immediate for STACK_FRAME_REGS_MARKER

Christophe Leroy christophe.leroy at csgroup.eu
Mon Sep 26 16:00:54 AEST 2022



Le 26/09/2022 à 05:40, Nicholas Piggin a écrit :
> Using a 32-bit constant for this marker allows it to be loaded with
> two ALU instructions, like 32-bit. This avoids a TOC entry and a
> TOC load that depends on the r2 value that has just been loaded from
> the PACA.
> 
> This changes the value for 32-bit as well, so both have the same
> value in the low 4 bytes and 64-bit has 0xffffffff in the top bytes.

The above is wrong now, isn't it ?

> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/include/asm/ptrace.h    | 4 ++--
>   arch/powerpc/kernel/entry_32.S       | 6 +++---
>   arch/powerpc/kernel/exceptions-64e.S | 8 +-------
>   arch/powerpc/kernel/exceptions-64s.S | 2 +-
>   arch/powerpc/kernel/head_64.S        | 7 -------
>   arch/powerpc/kernel/interrupt_64.S   | 6 +++---
>   6 files changed, 10 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index a03403695cd4..5b496e589d54 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -99,6 +99,8 @@ struct pt_regs
>   
>   #define STACK_FRAME_WITH_PT_REGS (STACK_FRAME_OVERHEAD + sizeof(struct pt_regs))
>   
> +#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x72656773)
> +
>   #ifdef __powerpc64__
>   
>   /*
> @@ -115,7 +117,6 @@ struct pt_regs
>   
>   #define STACK_FRAME_OVERHEAD	112	/* size of minimum stack frame */
>   #define STACK_FRAME_LR_SAVE	2	/* Location of LR in stack frame */
> -#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x7265677368657265)
>   #define STACK_INT_FRAME_SIZE	(sizeof(struct pt_regs) + \
>   				 STACK_FRAME_OVERHEAD + KERNEL_REDZONE_SIZE)
>   #define STACK_FRAME_MARKER	12
> @@ -136,7 +137,6 @@ struct pt_regs
>   #define KERNEL_REDZONE_SIZE	0
>   #define STACK_FRAME_OVERHEAD	16	/* size of minimum stack frame */
>   #define STACK_FRAME_LR_SAVE	1	/* Location of LR in stack frame */
> -#define STACK_FRAME_REGS_MARKER	ASM_CONST(0x72656773)
>   #define STACK_INT_FRAME_SIZE	(sizeof(struct pt_regs) + STACK_FRAME_OVERHEAD)
>   #define STACK_FRAME_MARKER	2
>   #define STACK_FRAME_MIN_SIZE	STACK_FRAME_OVERHEAD
> diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
> index 1d599df6f169..c2516f982cfa 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -265,7 +265,7 @@ fast_exception_return:
>   	mtcr	r10
>   	lwz	r10,_LINK(r11)
>   	mtlr	r10
> -	/* Clear the exception_marker on the stack to avoid confusing stacktrace */
> +	/* Clear the exception marker on the stack to avoid confusing stacktrace */
>   	li	r10, 0
>   	stw	r10, 8(r11)
>   	REST_GPR(10, r11)
> @@ -322,7 +322,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>   	li	r0,0
>   
>   	/*
> -	 * Leaving a stale exception_marker on the stack can confuse
> +	 * Leaving a stale exception marker on the stack can confuse
>   	 * the reliable stack unwinder later on. Clear it.
>   	 */
>   	stw	r0,8(r1)
> @@ -374,7 +374,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>   	mtspr	SPRN_XER,r5
>   
>   	/*
> -	 * Leaving a stale exception_marker on the stack can confuse
> +	 * Leaving a stale exception marker on the stack can confuse
>   	 * the reliable stack unwinder later on. Clear it.
>   	 */
>   	stw	r0,8(r1)
> diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
> index 67dc4e3179a0..08a3139079b7 100644
> --- a/arch/powerpc/kernel/exceptions-64e.S
> +++ b/arch/powerpc/kernel/exceptions-64e.S
> @@ -389,7 +389,7 @@ exc_##n##_common:							    \
>   	ld	r9,excf+EX_R1(r13);	/* load orig r1 back from PACA */   \
>   	lwz	r10,excf+EX_CR(r13);	/* load orig CR back from PACA	*/  \
>   	lbz	r11,PACAIRQSOFTMASK(r13); /* get current IRQ softe */	    \
> -	ld	r12,exception_marker at toc(r2);				    \
> +	LOAD_REG_IMMEDIATE(r12, STACK_FRAME_REGS_MARKER);		    \
>   	li	r0,0;							    \
>   	std	r3,GPR10(r1);		/* save r10 to stackframe */	    \
>   	std	r4,GPR11(r1);		/* save r11 to stackframe */	    \
> @@ -470,12 +470,6 @@ exc_##n##_bad_stack:							    \
>   	bl	hdlr;							\
>   	b	interrupt_return
>   
> -/* This value is used to mark exception frames on the stack. */
> -	.section	".toc","aw"
> -exception_marker:
> -	.tc	ID_EXC_MARKER[TC],STACK_FRAME_REGS_MARKER
> -
> -
>   /*
>    * And here we have the exception vectors !
>    */
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 3d0dc133a9ae..9d375ea58add 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -589,7 +589,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
>   	li	r9,IVEC
>   	std	r9,_TRAP(r1)		/* set trap number		*/
>   	li	r10,0
> -	ld	r11,exception_marker at toc(r2)
> +	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
>   	std	r10,RESULT(r1)		/* clear regs->result		*/
>   	std	r11,STACK_FRAME_OVERHEAD-16(r1) /* mark the frame	*/
>   .endm
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index cf2c08902c05..cac3e1b58360 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -192,13 +192,6 @@ __secondary_hold:
>   #endif
>   CLOSE_FIXED_SECTION(first_256B)
>   
> -/* This value is used to mark exception frames on the stack. */
> -	.section ".toc","aw"
> -/* This value is used to mark exception frames on the stack. */
> -exception_marker:
> -	.tc	ID_EXC_MARKER[TC],STACK_FRAME_REGS_MARKER
> -	.previous
> -
>   /*
>    * On server, we include the exception vectors code here as it
>    * relies on absolute addressing which is only possible within
> diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
> index ce25b28cf418..ee2d2d410c5a 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -92,7 +92,7 @@ _ASM_NOKPROBE_SYMBOL(system_call_vectored_\name)
>   	std	r11,_TRAP(r1)
>   	std	r12,_CCR(r1)
>   	addi	r10,r1,STACK_FRAME_OVERHEAD
> -	ld	r11,exception_marker at toc(r2)
> +	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
>   	std	r11,-16(r10)		/* "regshere" marker */
>   
>   BEGIN_FTR_SECTION
> @@ -276,7 +276,7 @@ END_BTB_FLUSH_SECTION
>   	std	r11,_TRAP(r1)
>   	std	r12,_CCR(r1)
>   	addi	r10,r1,STACK_FRAME_OVERHEAD
> -	ld	r11,exception_marker at toc(r2)
> +	LOAD_REG_IMMEDIATE(r11, STACK_FRAME_REGS_MARKER)
>   	std	r11,-16(r10)		/* "regshere" marker */
>   
>   #ifdef CONFIG_PPC_BOOK3S
> @@ -619,7 +619,7 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>   	mtspr	SPRN_XER,r5
>   
>   	/*
> -	 * Leaving a stale exception_marker on the stack can confuse
> +	 * Leaving a stale STACK_FRAME_REGS_MARKER on the stack can confuse
>   	 * the reliable stack unwinder later on. Clear it.
>   	 */
>   	std	r0,STACK_FRAME_OVERHEAD-16(r1)


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