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Message-ID: <e625dce5-092f-21d4-bc1d-12dfcd729b84@gmail.com>
Date:   Tue, 22 Nov 2022 16:56:06 +0800
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Subject: Re: [PATCH V2 3/3] riscv: ftrace: Reduce the detour code size to half
To:     guoren@kernel.org, arnd@arndb.de, palmer@rivosinc.com,
        rostedt@goodmis.org, andy.chiu@sifive.com, greentime.hu@sifive.com,
        zong.li@sifive.com, jrtc27@jrtc27.com, mingo@redhat.com,
        palmer@dabbelt.com
Cc:     linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, Guo Ren <guoren@linux.alibaba.com>
References: <20220921034910.3142465-1-guoren@kernel.org>
 <20220921034910.3142465-4-guoren@kernel.org>
From:   Song Shuai <suagrfillet@gmail.com>
In-Reply-To: <20220921034910.3142465-4-guoren@kernel.org>
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在 2022/9/21 11:49, guoren@kernel.org 写道:
> From: Guo Ren <guoren@linux.alibaba.com>
> 
> 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@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
>   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@gmail.com/

>   	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