linux-kernel - Re: [PATCH] x86/ftrace: Get rid of function

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Date:   Tue, 22 Oct 2019 13:38:42 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     tip-bot2 for Jiri Slaby <tip-bot2@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-arch@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] x86/ftrace: Get rid of function_hook

On 21. 10. 19, 16:10, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> function_hook is used as a better name than the default __fentry__
> which is the profiling counter which gcc adds before every function's
> prologue. Thus, it is not called from C and cannot have the same
> semantics as a pure C function - it saves/restores regs so that a C
> function can be called.
> 
> Drop the function_hook symbol and use __fentry__ directly for better
> alignment with gcc's documentation.
> 
> Switch the marking to SYM_CODE_START/_END which is reserved for
> non-standard, special functions.
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Jiri Slaby <jslaby@...e.cz>

On the top of Steven's comment:
Acked-by: Jiri Slaby <jslaby@...e.cz>

Thanks for taking care of this while my tooth was causing me pain.

> Cc: Jonathan Corbet <corbet@....net>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: linux-doc@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: x86@...nel.org
> ---
>  Documentation/asm-annotations.rst |  4 ++--
>  arch/x86/kernel/ftrace_32.S       |  8 +++-----
>  arch/x86/kernel/ftrace_64.S       | 13 ++++++-------
>  3 files changed, 11 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/asm-annotations.rst b/Documentation/asm-annotations.rst
> index 29ccd6e61fe5..f55c2bb74d00 100644
> --- a/Documentation/asm-annotations.rst
> +++ b/Documentation/asm-annotations.rst
> @@ -117,9 +117,9 @@ This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.
>    So in most cases, developers should write something like in the following
>    example, having some asm instructions in between the macros, of course::
>  
> -    SYM_FUNC_START(function_hook)
> +    SYM_FUNC_START(memset)
>          ... asm insns ...
> -    SYM_FUNC_END(function_hook)
> +    SYM_FUNC_END(memset)
>  
>    In fact, this kind of annotation corresponds to the now deprecated ``ENTRY``
>    and ``ENDPROC`` macros.
> diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
> index 8ed1f5d371f0..77be7e7e5e59 100644
> --- a/arch/x86/kernel/ftrace_32.S
> +++ b/arch/x86/kernel/ftrace_32.S
> @@ -12,18 +12,16 @@
>  #include <asm/frame.h>
>  #include <asm/asm-offsets.h>
>  
> -# define function_hook	__fentry__
> -EXPORT_SYMBOL(__fentry__)
> -
>  #ifdef CONFIG_FRAME_POINTER
>  # define MCOUNT_FRAME			1	/* using frame = true  */
>  #else
>  # define MCOUNT_FRAME			0	/* using frame = false */
>  #endif
>  
> -SYM_FUNC_START(function_hook)
> +SYM_CODE_START(__fentry__)
>  	ret
> -SYM_FUNC_END(function_hook)
> +SYM_CODE_END(__fentry__)
> +EXPORT_SYMBOL(__fentry__)
>  
>  SYM_CODE_START(ftrace_caller)
>  
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index 69c8d1b9119e..3029fe4f8547 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -14,9 +14,6 @@
>  	.code64
>  	.section .entry.text, "ax"
>  
> -# define function_hook	__fentry__
> -EXPORT_SYMBOL(__fentry__)
> -
>  #ifdef CONFIG_FRAME_POINTER
>  /* Save parent and function stack frames (rip and rbp) */
>  #  define MCOUNT_FRAME_SIZE	(8+16*2)
> @@ -132,9 +129,10 @@ EXPORT_SYMBOL(__fentry__)
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  
> -SYM_FUNC_START(function_hook)
> +SYM_CODE_START(__fentry__)
>  	retq
> -SYM_FUNC_END(function_hook)
> +SYM_CODE_END(__fentry__)
> +EXPORT_SYMBOL(__fentry__)
>  
>  SYM_FUNC_START(ftrace_caller)
>  	/* save_mcount_regs fills in first two parameters */
> @@ -248,7 +246,7 @@ SYM_FUNC_END(ftrace_regs_caller)
>  
>  #else /* ! CONFIG_DYNAMIC_FTRACE */
>  
> -SYM_FUNC_START(function_hook)
> +SYM_CODE_START(__fentry__)
>  	cmpq $ftrace_stub, ftrace_trace_function
>  	jnz trace
>  
> @@ -279,7 +277,8 @@ trace:
>  	restore_mcount_regs
>  
>  	jmp fgraph_trace
> -SYM_FUNC_END(function_hook)
> +SYM_CODE_END(__fentry__)
> +EXPORT_SYMBOL(__fentry__)
>  #endif /* CONFIG_DYNAMIC_FTRACE */
>  
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> 


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