Re: [RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER
From: Christophe Leroy <hidden>
Date: 2022-09-21 16:51:04
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
quoted hunk ↗ jump to hunk
Signed-off-by: Nicholas Piggin <npiggin@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_OVERHEADdiff --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@ha /* exception frame marker */ + li r12,STACK_FRAME_REGS_MARKER /* exception frame marker */ SAVE_GPR(2, r1) - addi r12,r12,STACK_FRAME_REGS_MARKER@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@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@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 */ .endmdiff --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@ha /* exception frame marker */ - addi r10,r10,STACK_FRAME_REGS_MARKER@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 withindiff --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@ha /* exception frame marker */ - addi r10, r10, STACK_FRAME_REGS_MARKER@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@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@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)