linux-kernel - Re: [PATCH v1 08/22] powerpc/ftrace: Make __ftrace_make

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Date:   Mon, 18 Apr 2022 12:10:04 +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 08/22] powerpc/ftrace: Make __ftrace_make_{nop/call}()
 common to PPC32 and PPC64

Christophe Leroy wrote:
> Since c93d4f6ecf4b ("powerpc/ftrace: Add module_trampoline_target()
> for PPC32"), __ftrace_make_nop() for PPC32 is very similar to the
> one for PPC64.
> 
> Same for __ftrace_make_call().
> 
> Make them common.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/kernel/trace/ftrace.c | 108 +++--------------------------
>  1 file changed, 8 insertions(+), 100 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 1b05d33f96c6..2c7e42e439bb 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -114,7 +114,6 @@ static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
>  }
> 
>  #ifdef CONFIG_MODULES
> -#ifdef CONFIG_PPC64
>  static int
>  __ftrace_make_nop(struct module *mod,
>  		  struct dyn_ftrace *rec, unsigned long addr)
> @@ -154,10 +153,11 @@ __ftrace_make_nop(struct module *mod,
>  		return -EINVAL;
>  	}
> 
> -#ifdef CONFIG_MPROFILE_KERNEL
> -	/* When using -mkernel_profile there is no load to jump over */
> +	/* When using -mkernel_profile or PPC32 there is no load to jump over */
                      -mprofile-kernel

Since you are modifying that line anyway ^^


>  	pop = ppc_inst(PPC_RAW_NOP());
> 
> +#ifdef CONFIG_PPC64
> +#ifdef CONFIG_MPROFILE_KERNEL
>  	if (copy_inst_from_kernel_nofault(&op, (void *)(ip - 4))) {
>  		pr_err("Fetching instruction at %lx failed.\n", ip - 4);
>  		return -EFAULT;
> @@ -201,6 +201,7 @@ __ftrace_make_nop(struct module *mod,
>  		return -EINVAL;
>  	}
>  #endif /* CONFIG_MPROFILE_KERNEL */
> +#endif /* PPC64 */
> 
>  	if (patch_instruction((u32 *)ip, pop)) {
>  		pr_err("Patching NOP failed.\n");
> @@ -209,48 +210,6 @@ __ftrace_make_nop(struct module *mod,
> 
>  	return 0;
>  }
> -
> -#else /* !PPC64 */
> -static int
> -__ftrace_make_nop(struct module *mod,
> -		  struct dyn_ftrace *rec, unsigned long addr)
> -{
> -	ppc_inst_t op;
> -	unsigned long ip = rec->ip;
> -	unsigned long tramp, ptr;
> -
> -	if (copy_from_kernel_nofault(&op, (void *)ip, MCOUNT_INSN_SIZE))
> -		return -EFAULT;
> -
> -	/* Make sure that that this is still a 24bit jump */
> -	if (!is_bl_op(op)) {
> -		pr_err("Not expected bl: opcode is %s\n", ppc_inst_as_str(op));
> -		return -EINVAL;
> -	}
> -
> -	/* lets find where the pointer goes */
> -	tramp = find_bl_target(ip, op);
> -
> -	/* Find where the trampoline jumps to */
> -	if (module_trampoline_target(mod, tramp, &ptr)) {
> -		pr_err("Failed to get trampoline target\n");
> -		return -EFAULT;
> -	}
> -
> -	if (ptr != addr) {
> -		pr_err("Trampoline location %08lx does not match addr\n",
> -		       tramp);
> -		return -EINVAL;
> -	}
> -
> -	op = ppc_inst(PPC_RAW_NOP());
> -
> -	if (patch_instruction((u32 *)ip, op))
> -		return -EPERM;
> -
> -	return 0;
> -}
> -#endif /* PPC64 */
>  #endif /* CONFIG_MODULES */
> 
>  static unsigned long find_ftrace_tramp(unsigned long ip)
> @@ -437,13 +396,12 @@ int ftrace_make_nop(struct module *mod,
>  }
> 
>  #ifdef CONFIG_MODULES
> -#ifdef CONFIG_PPC64
>  /*
>   * Examine the existing instructions for __ftrace_make_call.
>   * They should effectively be a NOP, and follow formal constraints,
>   * depending on the ABI. Return false if they don't.
>   */
> -#ifndef CONFIG_MPROFILE_KERNEL
> +#ifndef CONFIG_DYNAMIC_FTRACE_WITH_REGS

It is better to gate this on PPC64_ELF_ABI_v1

>  static int
>  expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>  {
> @@ -465,7 +423,7 @@ 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 */
> +	/* 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;
> @@ -484,8 +442,10 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
>  	if (copy_inst_from_kernel_nofault(op, ip))
>  		return -EFAULT;
> 
> +#ifndef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>  	if (copy_inst_from_kernel_nofault(op + 1, ip + 4))
>  		return -EFAULT;
> +#endif

Here too...


- Naveen