linux-kernel - Re: [PATCH v2] ftrace/x86: Remove jumps to ftrace

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Date:   Tue, 19 Jul 2022 15:19:16 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH v2] ftrace/x86: Remove jumps to ftrace_epilogue and
 simplify trampolines

On Tue, 19 Jul 2022 10:32:01 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 5b4efc927d80..7225ccca94b9 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -301,8 +301,6 @@ union ftrace_op_code_union {
>  	} __attribute__((packed));
>  };
>  
> -#define RET_SIZE		1 + IS_ENABLED(CONFIG_SLS)
> -
>  static unsigned long
>  create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>  {
> @@ -319,7 +317,6 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>  	void *ip;
>  	/* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
>  	unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
> -	unsigned const char retq[] = { RET_INSN_OPCODE, INT3_INSN_OPCODE };
>  	union ftrace_op_code_union op_ptr;
>  	int ret;
>  
> @@ -341,14 +338,14 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>  
>  	/*
>  	 * Allocate enough size to store the ftrace_caller code,
> -	 * the iret , as well as the address of the ftrace_ops this
> -	 * trampoline is used for.
> +	 * as well as the address of the ftrace_ops this trampoline
> +	 * is used for.
>  	 */
> -	trampoline = alloc_tramp(size + RET_SIZE + sizeof(void *));
> +	trampoline = alloc_tramp(size + sizeof(void *));
>  	if (!trampoline)
>  		return 0;
>  

Bah, I didn't realize that Linus already applied the retbleed patches. The
above conflicts.

I'll rebase it and send out a v3.

-- Steve