linux-kernel - Re: [PATCH v1 13/22] powerpc/ftrace: Use PPC_RAW

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Date:   Mon, 18 Apr 2022 13:08:44 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 13/22] powerpc/ftrace: Use PPC_RAW_xxx() macros instead
 of opencoding.

Christophe Leroy wrote:
> PPC_RAW_xxx() macros are self explanatory and less error prone
> than open coding.
> 
> Use them in ftrace.c
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/ppc-opcode.h |  3 +++
>  arch/powerpc/kernel/trace/ftrace.c    | 32 +++++++++------------------
>  2 files changed, 14 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
> index 82f1f0041c6f..281754aca0a3 100644
> --- a/arch/powerpc/include/asm/ppc-opcode.h
> +++ b/arch/powerpc/include/asm/ppc-opcode.h
> @@ -294,6 +294,8 @@
>  #define PPC_INST_BL			0x48000001
>  #define PPC_INST_BRANCH_COND		0x40800000
> 
> +#define PPC_INST_OFFSET24_MASK		0x03fffffc

This corresponds to the LI field, per the ISA. See section 8.1.2/1.7: 
'Instruction Fields'. Would it be better to name it PPC_INST_LI_MASK?

> +
>  /* Prefixes */
>  #define PPC_INST_LFS			0xc0000000
>  #define PPC_INST_STFS			0xd0000000
> @@ -572,6 +574,7 @@
>  #define PPC_RAW_EIEIO()			(0x7c0006ac)
> 
>  #define PPC_RAW_BRANCH(addr)		(PPC_INST_BRANCH | ((addr) & 0x03fffffc))
> +#define PPC_RAW_BL(offset)		(0x48000001 | ((offset) & PPC_INST_OFFSET24_MASK))
> 
>  /* Deal with instructions that older assemblers aren't aware of */
>  #define	PPC_BCCTR_FLUSH		stringify_in_c(.long PPC_INST_BCCTR_FLUSH)
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index fdc0412c1d8a..afb1d12838c9 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -90,19 +90,19 @@ static int test_24bit_addr(unsigned long ip, unsigned long addr)
> 
>  static int is_bl_op(ppc_inst_t op)
>  {
> -	return (ppc_inst_val(op) & 0xfc000003) == 0x48000001;
> +	return (ppc_inst_val(op) & ~PPC_INST_OFFSET24_MASK) == PPC_RAW_BL(0);
>  }
> 
>  static int is_b_op(ppc_inst_t op)
>  {
> -	return (ppc_inst_val(op) & 0xfc000003) == 0x48000000;
> +	return (ppc_inst_val(op) & ~PPC_INST_OFFSET24_MASK) == PPC_RAW_BRANCH(0);
>  }
> 
>  static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
>  {
>  	int offset;
> 
> -	offset = (ppc_inst_val(op) & 0x03fffffc);
> +	offset = (ppc_inst_val(op) & PPC_INST_OFFSET24_MASK);
>  	/* make it signed */
>  	if (offset & 0x02000000)
>  		offset |= 0xfe000000;
> @@ -182,7 +182,7 @@ __ftrace_make_nop(struct module *mod,
>  	 * Use a b +8 to jump over the load.
>  	 */
> 
> -	pop = ppc_inst(PPC_INST_BRANCH | 8);	/* b +8 */
> +	pop = ppc_inst(PPC_RAW_BRANCH(8));	/* b +8 */
> 
>  	/*
>  	 * Check what is in the next instruction. We can see ld r2,40(r1), but
> @@ -394,17 +394,8 @@ int ftrace_make_nop(struct module *mod,
>  static int
>  expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>  {
> -	/*
> -	 * We expect to see:
> -	 *
> -	 * b +8
> -	 * ld r2,XX(r1)
> -	 *
> -	 * The load offset is different depending on the ABI. For simplicity
> -	 * just mask it out when doing the compare.
> -	 */
> -	if (!ppc_inst_equal(op0, ppc_inst(0x48000008)) ||
> -	    (ppc_inst_val(op1) & 0xffff0000) != 0xe8410000)
> +	if (!ppc_inst_equal(op0, ppc_inst(PPC_RAW_BRANCH(8))) ||
> +	    !ppc_inst_equal(op1, ppc_inst(PPC_INST_LD_TOC)))

It would be good to move PPC_INST_LD_TOC to ppc-opcode.h

>  		return 0;
>  	return 1;
>  }
> @@ -412,7 +403,6 @@ expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>  static int
>  expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>  {
> -	/* look for patched "NOP" on ppc64 with -mprofile-kernel or ppc32 */
>  	if (!ppc_inst_equal(op0, ppc_inst(PPC_RAW_NOP())))
>  		return 0;
>  	return 1;
> @@ -738,11 +728,11 @@ int __init ftrace_dyn_arch_init(void)
>  	int i;
>  	unsigned int *tramp[] = { ftrace_tramp_text, ftrace_tramp_init };
>  	u32 stub_insns[] = {
> -		0xe98d0000 | PACATOC,	/* ld      r12,PACATOC(r13)	*/
> -		0x3d8c0000,		/* addis   r12,r12,<high>	*/
> -		0x398c0000,		/* addi    r12,r12,<low>	*/
> -		0x7d8903a6,		/* mtctr   r12			*/
> -		0x4e800420,		/* bctr				*/
> +		PPC_RAW_LD(_R12, _R13, PACATOC),
> +		PPC_RAW_ADDIS(_R12, _R12, 0),
> +		PPC_RAW_ADDIS(_R12, _R12, 0),

This should be PPC_RAW_ADDI.


- Naveen