linux-kernel - Re: [PATCH] function:stacktrace/mips: Fix function:stacktrace for mips

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Date:   Thu, 4 Jun 2020 02:17:47 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@....com>
To:     WANG Xuerui <kernel@...0n.name>
cc:     yuanjunqing <yuanjunqing66@....com>, tsbogend@...ha.franken.de,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        liulichao@...ngson.cn, "Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH] function:stacktrace/mips: Fix function:stacktrace for
 mips

On Fri, 29 May 2020, WANG Xuerui wrote:

> On 2020/5/29 17:29, yuanjunqing wrote:
> 
> >> diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
> >> index cff52b283e03..cd5545764e5f 100644
> >> --- a/arch/mips/kernel/mcount.S
> >> +++ b/arch/mips/kernel/mcount.S
> >> @@ -87,8 +87,15 @@ EXPORT_SYMBOL(_mcount)
> >>   	PTR_LA   t1, _etext
> >>   	sltu     t3, t1, a0	/* t3 = (a0 > _etext) */
> >>   	or       t1, t2, t3
> >> +	PTR_LA	 t2, stlab-4 	/* t2: "function:stacktrace" return address */
> >> +	move	 a1, AT		/* arg2: parent's return address */
> >>   	beqz     t1, ftrace_call
> >> -	 nop
> >> +	 nop			/* "function:stacktrace" return address */
> >> +stlab:
> >> +	PTR_LA	t2, stlab-4
> >> +	/* ftrace_call_end: ftrace_call return address */
> >> +	beq	t2,ra, ftrace_call_end
> >> +	nop

 Broken delay slot indentation.

> >>   #if defined(KBUILD_MCOUNT_RA_ADDRESS) && defined(CONFIG_32BIT)
> >>   	PTR_SUBU a0, a0, 16	/* arg1: adjust to module's recorded callsite */
> >>   #else
> >> @@ -98,7 +105,9 @@ EXPORT_SYMBOL(_mcount)
> >>   	.globl ftrace_call
> >>   ftrace_call:
> >>   	nop	/* a placeholder for the call to a real tracing function */
> >> -	 move	a1, AT		/* arg2: parent's return address */
> >> +	move	ra, t2		/* t2: "function:stacktrace" return address */

 Likewise.  NB I haven't investigated if the change makes sense.  A more 
detailed explanation in the change description is certainly needed.

  Maciej