[RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER

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From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail.com>, Alan Modra <amodra@gmail.com>
Subject: [RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER
Date: Tue, 20 Sep 2022 00:01:43 +1000	[thread overview]
Message-ID: <20220919140149.4018927-2-npiggin@gmail.com> (raw)
In-Reply-To: <20220919140149.4018927-1-npiggin@gmail.com>

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@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@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	*/
 .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@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 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@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)
-- 
2.37.2

next prev parent reply	other threads:[~2022-09-19 14:03 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-19 14:01 [RFC PATCH 0/7] powerpc: first hack at pcrel addressing Nicholas Piggin
2022-09-19 14:01 ` Nicholas Piggin [this message]
2022-09-21 16:49   ` [RFC PATCH 1/7] powerpc: use 16-bit immediate for STACK_FRAME_REGS_MARKER Christophe Leroy
2022-09-23  7:32     ` Michael Ellerman
2022-09-23  7:35       ` Christophe Leroy
2022-09-19 14:01 ` [RFC PATCH 2/7] powerpc/64: abstract asm global variable declaration and access Nicholas Piggin
2022-09-21 16:51   ` Christophe Leroy
2022-09-19 14:01 ` [RFC PATCH 3/7] powerpc/64: provide a helper macro to load r2 with the kernel TOC Nicholas Piggin
2022-09-21 16:52   ` Christophe Leroy
2022-09-19 14:01 ` [RFC PATCH 4/7] powerpc: add CFUNC assembly label annotation Nicholas Piggin
2022-09-19 14:01 ` [RFC PATCH 5/7] powerpc/64s: update generic cpu option name and compiler flags Nicholas Piggin
2022-09-20 22:16   ` Segher Boessenkool
2022-09-21  1:01     ` Nicholas Piggin
2022-09-21 15:22       ` Segher Boessenkool
2022-09-23  7:22         ` Nicholas Piggin
2022-09-19 14:01 ` [RFC PATCH 6/7] powerpc/64s: POWER10 CPU Kconfig build option Nicholas Piggin
2022-09-19 14:01 ` [RFC PATCH 7/7] powerpc/64s: Add option to build vmlinux with pcrel addressing Nicholas Piggin

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