[RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER
Christophe Leroy
christophe.leroy at csgroup.eu
Thu Sep 22 02:49:57 AEST 2022
Le 19/09/2022 à 16:01, Nicholas Piggin a écrit :
> Using a 16-bit constant for this marker allows it to be loaded with
> a single 'li' instruction. On 64-bit this avoids a TOC entry and a
> TOC load that depends on the r2 value that has just been loaded from
> the PACA.
>
> XXX: this probably should be 64-bit change and use 2 instruction
> sequence that 32-bit uses, to avoid false positives.
Yes would probably be safer ? It is only one instruction more, would
likely be unnoticeable.
Why value 0xffffba51 ?
Why not 0xffffdead like PPC64 ?
Christophe
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> arch/powerpc/include/asm/ptrace.h | 6 +++---
> arch/powerpc/kernel/entry_32.S | 9 ++++-----
> arch/powerpc/kernel/exceptions-64e.S | 8 +-------
> arch/powerpc/kernel/exceptions-64s.S | 2 +-
> arch/powerpc/kernel/head_32.h | 3 +--
> arch/powerpc/kernel/head_64.S | 7 -------
> arch/powerpc/kernel/head_booke.h | 3 +--
> arch/powerpc/kernel/interrupt_64.S | 6 +++---
> 8 files changed, 14 insertions(+), 30 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index a03403695cd4..f47066f7878e 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -115,10 +115,10 @@ 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_FRAME_REGS_MARKER ASM_CONST(0xffffffffffffdead)
> #define STACK_INT_FRAME_SIZE (sizeof(struct pt_regs) + \
> STACK_FRAME_OVERHEAD + KERNEL_REDZONE_SIZE)
> -#define STACK_FRAME_MARKER 12
> +#define STACK_FRAME_MARKER 1 /* Reuse CR+reserved word */
>
> #ifdef CONFIG_PPC64_ELF_ABI_V2
> #define STACK_FRAME_MIN_SIZE 32
> @@ -136,7 +136,7 @@ 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_FRAME_REGS_MARKER ASM_CONST(0xffffba51)
> #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..c221e764cefd 100644
> --- a/arch/powerpc/kernel/entry_32.S
> +++ b/arch/powerpc/kernel/entry_32.S
> @@ -108,9 +108,8 @@ transfer_to_syscall:
> #ifdef CONFIG_BOOKE_OR_40x
> rlwinm r9,r9,0,14,12 /* clear MSR_WE (necessary?) */
> #endif
> - lis r12,STACK_FRAME_REGS_MARKER at ha /* exception frame marker */
> + li r12,STACK_FRAME_REGS_MARKER /* exception frame marker */
> SAVE_GPR(2, r1)
> - addi r12,r12,STACK_FRAME_REGS_MARKER at l
> stw r9,_MSR(r1)
> li r2, INTERRUPT_SYSCALL
> stw r12,8(r1)
> @@ -265,7 +264,7 @@ fast_exception_return:
> mtcr r10
> lwz r10,_LINK(r11)
> mtlr r10
> - /* Clear the exception_marker on the stack to avoid confusing stacktrace */
> + /* Clear the STACK_FRAME_REGS_MARKER on the stack to avoid confusing stacktrace */
> li r10, 0
> stw r10, 8(r11)
> REST_GPR(10, r11)
> @@ -322,7 +321,7 @@ 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 STACK_FRAME_REGS_MARKER on the stack can confuse
> * the reliable stack unwinder later on. Clear it.
> */
> stw r0,8(r1)
> @@ -374,7 +373,7 @@ 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.
> */
> stw r0,8(r1)
> diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
> index 67dc4e3179a0..08b7d6bd4da6 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); \
> + li 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..5c110e5e5819 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)
> + li 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_32.h b/arch/powerpc/kernel/head_32.h
> index c3286260a7d1..5cf80f29d839 100644
> --- a/arch/powerpc/kernel/head_32.h
> +++ b/arch/powerpc/kernel/head_32.h
> @@ -110,8 +110,7 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
>
> .macro COMMON_EXCEPTION_PROLOG_END trapno
> stw r0,GPR0(r1)
> - lis r10,STACK_FRAME_REGS_MARKER at ha /* exception frame marker */
> - addi r10,r10,STACK_FRAME_REGS_MARKER at l
> + li r10,STACK_FRAME_REGS_MARKER /* exception frame marker */
> stw r10,8(r1)
> li r10, \trapno
> stw r10,_TRAP(r1)
> 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/head_booke.h b/arch/powerpc/kernel/head_booke.h
> index bb6d5d0fc4ac..fe36237197c2 100644
> --- a/arch/powerpc/kernel/head_booke.h
> +++ b/arch/powerpc/kernel/head_booke.h
> @@ -82,8 +82,7 @@ END_BTB_FLUSH_SECTION
>
> .macro COMMON_EXCEPTION_PROLOG_END trapno
> stw r0,GPR0(r1)
> - lis r10, STACK_FRAME_REGS_MARKER at ha /* exception frame marker */
> - addi r10, r10, STACK_FRAME_REGS_MARKER at l
> + li r10, STACK_FRAME_REGS_MARKER /* exception frame marker */
> stw r10, 8(r1)
> li r10, \trapno
> stw r10,_TRAP(r1)
> diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
> index ce25b28cf418..14c409fd4c38 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)
> + li 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)
> + li 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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