Re: [PATCH V2 3/3] riscv: ftrace: Reduce the detour code size to half

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在 2022/9/21 11:49, guoren@xxxxxxxxxx 写道:
From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

Use a temporary register to reduce the size of detour code from 16B
to 8B.

Before optimization (16 byte):
<func_prolog>:
  0: REG_S  ra, -SZREG(sp)
  4: auipc  ra, ?
  8: jalr   ?(ra)
12: REG_L  ra, -SZREG(sp)
  (func_boddy)

The previous implementation is from afc76b8b8011 ("riscv: Using
PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")

After optimization (8 byte):
<func_prolog>:
  0: auipc  t0, ?
  4: jalr   t0, ?(t0)
  (func_boddy)

Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
  arch/riscv/Makefile             |  4 +-
  arch/riscv/include/asm/ftrace.h | 46 ++++++++++++++++++-----
  arch/riscv/kernel/ftrace.c      | 65 ++++++++++-----------------------
  arch/riscv/kernel/mcount-dyn.S  | 43 +++++++++-------------
  4 files changed, 74 insertions(+), 84 deletions(-)

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index f32844f545d6..7b9d4a7cd4bf 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -12,9 +12,9 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
  	LDFLAGS_vmlinux := --no-relax
  	KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
  ifeq ($(CONFIG_RISCV_ISA_C),y)
-	CC_FLAGS_FTRACE := -fpatchable-function-entry=8
-else
  	CC_FLAGS_FTRACE := -fpatchable-function-entry=4
+else
+	CC_FLAGS_FTRACE := -fpatchable-function-entry=2
  endif
  endif
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 04dad3380041..34b0b523865a 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -42,6 +42,14 @@ struct dyn_arch_ftrace {
   * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to
   *          return address (original pc + 4)
   *
+ *<ftrace enable>:
+ * 0: auipc  t0/ra, 0x?
+ * 4: jalr   t0/ra, ?(t0/ra)
+ *
+ *<ftrace disable>:
+ * 0: nop
+ * 4: nop
+ *
   * Dynamic ftrace generates probes to call sites, so we must deal with
   * both auipc and jalr at the same time.
   */
@@ -52,25 +60,43 @@ struct dyn_arch_ftrace {
  #define AUIPC_OFFSET_MASK	(0xfffff000)
  #define AUIPC_PAD		(0x00001000)
  #define JALR_SHIFT		20
-#define JALR_BASIC		(0x000080e7)
-#define AUIPC_BASIC		(0x00000097)
+#define JALR_RA			(0x000080e7)
+#define AUIPC_RA		(0x00000097)
+#define JALR_T0			(0x000282e7)
+#define AUIPC_T0		(0x00000297)
  #define NOP4			(0x00000013)
-#define make_call(caller, callee, call) \
+#define to_jalr_t0(offset)						\
+	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0)
+
+#define to_auipc_t0(offset)						\
+	((offset & JALR_SIGN_MASK) ?					\
+	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_T0) :	\
+	((offset & AUIPC_OFFSET_MASK) | AUIPC_T0))
+
+#define make_call_t0(caller, callee, call)				\
  do {									\
-	call[0] = to_auipc_insn((unsigned int)((unsigned long)callee -	\
+	call[0] = to_auipc_t0((unsigned int)((unsigned long)callee -	\
  				(unsigned long)caller));		\
-	call[1] = to_jalr_insn((unsigned int)((unsigned long)callee -	\
+	call[1] = to_jalr_t0((unsigned int)((unsigned long)callee -	\
  			       (unsigned long)caller));			\
  } while (0)
-#define to_jalr_insn(offset) \
-	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC)
+#define to_jalr_ra(offset)						\
+	(((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA)
-#define to_auipc_insn(offset) \
+#define to_auipc_ra(offset)					\
  	((offset & JALR_SIGN_MASK) ?					\
-	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) :	\
-	((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC))
+	(((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) :	\
+	((offset & AUIPC_OFFSET_MASK) | AUIPC_RA))
+
+#define make_call_ra(caller, callee, call)				\
+do {									\
+	call[0] = to_auipc_ra((unsigned int)((unsigned long)callee -	\
+				(unsigned long)caller));		\
+	call[1] = to_jalr_ra((unsigned int)((unsigned long)callee -	\
+			       (unsigned long)caller));			\
+} while (0)
/*
   * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 2086f6585773..8c77f236fc71 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -55,12 +55,15 @@ static int ftrace_check_current_call(unsigned long hook_pos,
  }
static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
-				bool enable)
+				bool enable, bool ra)
  {
  	unsigned int call[2];
  	unsigned int nops[2] = {NOP4, NOP4};
- make_call(hook_pos, target, call);
+	if (ra)
+		make_call_ra(hook_pos, target, call);
+	else
+		make_call_t0(hook_pos, target, call);
/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
  	if (patch_text_nosync
@@ -70,42 +73,13 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
  	return 0;
  }
-/*
- * Put 5 instructions with 16 bytes at the front of function within
- * patchable function entry nops' area.
- *
- * 0: REG_S  ra, -SZREG(sp)
- * 1: auipc  ra, 0x?
- * 2: jalr   -?(ra)
- * 3: REG_L  ra, -SZREG(sp)
- *
- * So the opcodes is:
- * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
- * 1: 0x???????? -> auipc
- * 2: 0x???????? -> jalr
- * 3: 0xff813083 (ld)/0xffc12083 (lw)
- */
-#if __riscv_xlen == 64
-#define INSN0	0xfe113c23
-#define INSN3	0xff813083
-#elif __riscv_xlen == 32
-#define INSN0	0xfe112e23
-#define INSN3	0xffc12083
-#endif
-
-#define FUNC_ENTRY_SIZE	16
-#define FUNC_ENTRY_JMP	4
-
  int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
  {
-	unsigned int call[4] = {INSN0, 0, 0, INSN3};
-	unsigned long target = addr;
-	unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+	unsigned int call[2];
- call[1] = to_auipc_insn((unsigned int)(target - caller));
-	call[2] = to_jalr_insn((unsigned int)(target - caller));
+	make_call_t0(rec->ip, addr, call);
- if (patch_text_nosync((void *)rec->ip, call, FUNC_ENTRY_SIZE))
+	if (patch_text_nosync((void *)rec->ip, call, 8))
  		return -EPERM;
return 0;
@@ -114,15 +88,14 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
  int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
  		    unsigned long addr)
  {
-	unsigned int nops[4] = {NOP4, NOP4, NOP4, NOP4};
+	unsigned int nops[2] = {NOP4, NOP4};
- if (patch_text_nosync((void *)rec->ip, nops, FUNC_ENTRY_SIZE))
+	if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
  		return -EPERM;
return 0;
  }
-
  /*
   * This is called early on, and isn't wrapped by
   * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
@@ -144,10 +117,10 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
  int ftrace_update_ftrace_func(ftrace_func_t func)
  {
  	int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
-				       (unsigned long)func, true);
+				       (unsigned long)func, true, true);
  	if (!ret) {
  		ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
-					   (unsigned long)func, true);
+					   (unsigned long)func, true, true);
  	}
return ret;
@@ -159,16 +132,16 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
  		       unsigned long addr)
  {
  	unsigned int call[2];
-	unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+	unsigned long caller = rec->ip + 4;
The caller should be assigned by rec->ip directly to indicate the function entry, otherwise ftrace bug will be triggered.

You can refer to this patch for details:

https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@xxxxxxxxx/

  	int ret;
- make_call(caller, old_addr, call);
+	make_call_t0(caller, old_addr, call);
  	ret = ftrace_check_current_call(caller, call);
if (ret)
  		return ret;
- return __ftrace_modify_call(caller, addr, true);
+	return __ftrace_modify_call(caller, addr, true, false);
  }
  #endif
@@ -203,12 +176,12 @@ int ftrace_enable_ftrace_graph_caller(void)
  	int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
-				    (unsigned long)&prepare_ftrace_return, true);
+				    (unsigned long)&prepare_ftrace_return, true, true);
  	if (ret)
  		return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
-				    (unsigned long)&prepare_ftrace_return, true);
+				    (unsigned long)&prepare_ftrace_return, true, true);
  }
int ftrace_disable_ftrace_graph_caller(void)
@@ -216,12 +189,12 @@ int ftrace_disable_ftrace_graph_caller(void)
  	int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
-				    (unsigned long)&prepare_ftrace_return, false);
+				    (unsigned long)&prepare_ftrace_return, false, true);
  	if (ret)
  		return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
-				    (unsigned long)&prepare_ftrace_return, false);
+				    (unsigned long)&prepare_ftrace_return, false, true);
  }
  #endif /* CONFIG_DYNAMIC_FTRACE */
  #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index d171eca623b6..64bc79816f5e 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -13,8 +13,8 @@
.text -#define FENTRY_RA_OFFSET 12
-#define ABI_SIZE_ON_STACK	72
+#define FENTRY_RA_OFFSET	8
+#define ABI_SIZE_ON_STACK	80
  #define ABI_A0			0
  #define ABI_A1			8
  #define ABI_A2			16
@@ -23,10 +23,10 @@
  #define ABI_A5			40
  #define ABI_A6			48
  #define ABI_A7			56
-#define ABI_RA			64
+#define ABI_T0			64
+#define ABI_RA			72
.macro SAVE_ABI
-	addi	sp, sp, -SZREG
  	addi	sp, sp, -ABI_SIZE_ON_STACK
REG_S a0, ABI_A0(sp)
@@ -37,6 +37,7 @@
  	REG_S	a5, ABI_A5(sp)
  	REG_S	a6, ABI_A6(sp)
  	REG_S	a7, ABI_A7(sp)
+	REG_S	t0, ABI_T0(sp)
  	REG_S	ra, ABI_RA(sp)
  	.endm
@@ -49,24 +50,18 @@
  	REG_L	a5, ABI_A5(sp)
  	REG_L	a6, ABI_A6(sp)
  	REG_L	a7, ABI_A7(sp)
+	REG_L	t0, ABI_T0(sp)
  	REG_L	ra, ABI_RA(sp)
addi sp, sp, ABI_SIZE_ON_STACK
-	addi	sp, sp, SZREG
  	.endm
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
  	.macro SAVE_ALL
-	addi	sp, sp, -SZREG
  	addi	sp, sp, -PT_SIZE_ON_STACK
- REG_S x1, PT_EPC(sp)
-	addi	sp, sp, PT_SIZE_ON_STACK
-	REG_L x1,  (sp)
-	addi	sp, sp, -PT_SIZE_ON_STACK
+	REG_S t0,  PT_EPC(sp)
  	REG_S x1,  PT_RA(sp)
-	REG_L x1,  PT_EPC(sp)
-
  	REG_S x2,  PT_SP(sp)
  	REG_S x3,  PT_GP(sp)
  	REG_S x4,  PT_TP(sp)
@@ -100,11 +95,8 @@
  	.endm
.macro RESTORE_ALL
+	REG_L t0,  PT_EPC(sp)
  	REG_L x1,  PT_RA(sp)
-	addi	sp, sp, PT_SIZE_ON_STACK
-	REG_S x1,  (sp)
-	addi	sp, sp, -PT_SIZE_ON_STACK
-	REG_L x1,  PT_EPC(sp)
  	REG_L x2,  PT_SP(sp)
  	REG_L x3,  PT_GP(sp)
  	REG_L x4,  PT_TP(sp)
@@ -137,17 +129,16 @@
  	REG_L x31, PT_T6(sp)
addi sp, sp, PT_SIZE_ON_STACK
-	addi	sp, sp, SZREG
  	.endm
  #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
ENTRY(ftrace_caller)
  	SAVE_ABI
- addi a0, ra, -FENTRY_RA_OFFSET
+	addi	a0, t0, -FENTRY_RA_OFFSET
  	la	a1, function_trace_op
  	REG_L	a2, 0(a1)
-	REG_L	a1, ABI_SIZE_ON_STACK(sp)
+	mv	a1, ra
  	mv	a3, sp
ftrace_call:
@@ -155,8 +146,8 @@ ftrace_call:
  	call	ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-	addi	a0, sp, ABI_SIZE_ON_STACK
-	REG_L	a1, ABI_RA(sp)
+	addi	a0, sp, ABI_RA
+	REG_L	a1, ABI_T0(sp)
  	addi	a1, a1, -FENTRY_RA_OFFSET
  #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
  	mv	a2, s0
@@ -166,17 +157,17 @@ ftrace_graph_call:
  	call	ftrace_stub
  #endif
  	RESTORE_ABI
-	ret
+	jr t0
  ENDPROC(ftrace_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
  ENTRY(ftrace_regs_caller)
  	SAVE_ALL
- addi a0, ra, -FENTRY_RA_OFFSET
+	addi	a0, t0, -FENTRY_RA_OFFSET
  	la	a1, function_trace_op
  	REG_L	a2, 0(a1)
-	REG_L	a1, PT_SIZE_ON_STACK(sp)
+	REG_L	a1, PT_RA(sp)
  	mv	a3, sp
ftrace_regs_call:
@@ -185,7 +176,7 @@ ftrace_regs_call:
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
  	addi	a0, sp, PT_RA
-	REG_L	a1, PT_EPC(sp)
+	REG_L	a1, PT_T0(sp)
  	addi	a1, a1, -FENTRY_RA_OFFSET
  #ifdef HAVE_FUNCTION_GRAPH_FP_TEST
  	mv	a2, s0
@@ -196,6 +187,6 @@ ftrace_graph_regs_call:
  #endif
RESTORE_ALL
-	ret
+	jr t0
  ENDPROC(ftrace_regs_caller)
  #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */

Thanks,
Song



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