linux-kernel - Re: [patch V4 part 2 02/18] x86/entry/32: Move non entry code into .text section

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Date:   Thu, 7 May 2020 15:15:27 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 2 02/18] x86/entry/32: Move non entry code into
 .text section


On 5/5/20 3:41 PM, Thomas Gleixner wrote:
> All ASM code which is not part of the entry functionality can move out into
> the .text section. No reason to keep it in the non-instrumentable entry
> section.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>   arch/x86/entry/entry_32.S |   11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -729,7 +729,8 @@
>   /*
>    * %eax: prev task
>    * %edx: next task
> - */
> +*/

Misaligned comment end, this line shouldn't change.

alex.

> +.pushsection .text, "ax"
>   SYM_CODE_START(__switch_to_asm)
>   	/*
>   	 * Save callee-saved registers
> @@ -776,6 +777,7 @@ SYM_CODE_START(__switch_to_asm)
>   
>   	jmp	__switch_to
>   SYM_CODE_END(__switch_to_asm)
> +.popsection
>   
>   /*
>    * The unwinder expects the last frame on the stack to always be at the same
> @@ -784,6 +786,7 @@ SYM_CODE_END(__switch_to_asm)
>    * asmlinkage function so its argument has to be pushed on the stack.  This
>    * wrapper creates a proper "end of stack" frame header before the call.
>    */
> +.pushsection .text, "ax"
>   SYM_FUNC_START(schedule_tail_wrapper)
>   	FRAME_BEGIN
>   
> @@ -794,6 +797,8 @@ SYM_FUNC_START(schedule_tail_wrapper)
>   	FRAME_END
>   	ret
>   SYM_FUNC_END(schedule_tail_wrapper)
> +.popsection
> +
>   /*
>    * A newly forked process directly context switches into this address.
>    *
> @@ -801,6 +806,7 @@ SYM_FUNC_END(schedule_tail_wrapper)
>    * ebx: kernel thread func (NULL for user thread)
>    * edi: kernel thread arg
>    */
> +.pushsection .text, "ax"
>   SYM_CODE_START(ret_from_fork)
>   	call	schedule_tail_wrapper
>   
> @@ -825,6 +831,7 @@ SYM_CODE_START(ret_from_fork)
>   	movl	$0, PT_EAX(%esp)
>   	jmp	2b
>   SYM_CODE_END(ret_from_fork)
> +.popsection
>   
>   /*
>    * Return to user mode is not as complex as all this looks,
> @@ -1693,6 +1700,7 @@ SYM_CODE_START(general_protection)
>   	jmp	common_exception
>   SYM_CODE_END(general_protection)
>   
> +.pushsection .text, "ax"
>   SYM_CODE_START(rewind_stack_do_exit)
>   	/* Prevent any naive code from trying to unwind to our caller. */
>   	xorl	%ebp, %ebp
> @@ -1703,3 +1711,4 @@ SYM_CODE_START(rewind_stack_do_exit)
>   	call	do_exit
>   1:	jmp 1b
>   SYM_CODE_END(rewind_stack_do_exit)
> +.popsection
>