[RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER
Nicholas Piggin
npiggin at gmail.com
Tue Sep 20 00:01:43 AEST 2022
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.
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)
--
2.37.2
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