linux-kernel - Re: [PATCH v2 2/2] arch: m68k: Add STACKTRACE support

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Message-ID: <eb313fe1-f586-4613-acb6-63b12859da71@gmail.com>
Date: Wed, 4 Dec 2024 07:21:46 +1300
From: Michael Schmitz <schmitzmic@...il.com>
To: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, rostedt@...dmis.org
Subject: Re: [PATCH v2 2/2] arch: m68k: Add STACKTRACE support

Jean-Michel,

good work on adding

On 4/12/24 06:21, Jean-Michel Hautbois wrote:
> In order to use tracing, implement a basic arch_stack_walk() based on
> the one in PowerPC.
> Tested on a M54418 coldfire.
>
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
> ---
>   arch/m68k/Kconfig             |  6 ++++
>   arch/m68k/kernel/Makefile     |  1 +
>   arch/m68k/kernel/stacktrace.c | 70 +++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 77 insertions(+)
>
> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
> index 793ab1e2762609725bbf793f6dffecfa3ecfff0f..6ba3238ba2c68acaf5974396739e629b09eee3ca 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -40,6 +40,8 @@ config M68K
>   	select UACCESS_MEMCPY if !MMU
>   	select ZONE_DMA
>   	select TRACE_IRQFLAGS_SUPPORT
> +	select ARCH_STACKWALK
> +	select ARCH_WANT_FRAME_POINTERS

How much does that add to kernel size? It's only needed for debugging so 
some folks may prefer to save a little on code size (not to mention the 
extra frame pointer save on each call) ...

Cheers,

     Michael


>   
>   config CPU_BIG_ENDIAN
>   	def_bool y
> @@ -106,6 +108,10 @@ config BOOTINFO_PROC
>   	  Say Y to export the bootinfo used to boot the kernel in a
>   	  "bootinfo" file in procfs.  This is useful with kexec.
>   
> +config STACKTRACE_SUPPORT
> +	bool
> +	default y
> +
Any reason why you can't place the two 'select' statements in this 
conditional?
>   menu "Platform setup"
>   
>   source "arch/m68k/Kconfig.cpu"
> diff --git a/arch/m68k/kernel/Makefile b/arch/m68k/kernel/Makefile
> index 6c732ed3998b714a4842ee29c977550a61979779..cb02bcfe04c6b265fa97db9237395a262e649989 100644
> --- a/arch/m68k/kernel/Makefile
> +++ b/arch/m68k/kernel/Makefile
> @@ -23,3 +23,4 @@ obj-$(CONFIG_UBOOT)		+= uboot.o
>   
>   obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
>   
> +obj-y	+= stacktrace.o
> diff --git a/arch/m68k/kernel/stacktrace.c b/arch/m68k/kernel/stacktrace.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..4c2fb6b0cf675ee5a3a21393a50603fea98a1b03
> --- /dev/null
> +++ b/arch/m68k/kernel/stacktrace.c
> @@ -0,0 +1,70 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Stack trace utility functions etc.
> + *
> + * Copyright 2024 Jean-Michel Hautbois, Yoseli SAS.
> + */
> +
> +#include <asm/current.h>
> +#include <asm/ptrace.h>
> +#include <linux/sched.h>
> +#include <linux/sched/task_stack.h>
> +#include <linux/stacktrace.h>
> +
> +static inline unsigned long current_stack_frame(void)
> +{
> +	unsigned long sp;
> +
> +	asm volatile("movl %%fp, %0" : "=r"(sp));
> +	return sp;
> +}
> +
> +static inline int validate_sp(unsigned long sp, struct task_struct *task)
> +{
> +	unsigned long stack_start, stack_end;
> +
> +	if (task == current)
> +		stack_start = (unsigned long)task_stack_page(task);
> +	else
> +		stack_start = (unsigned long)task->thread.esp0;
> +
> +	stack_end = stack_start + THREAD_SIZE;
> +
> +	if (sp < stack_start || sp >= stack_end)
> +		return 0;
> +
> +	return 1;
> +}
> +
> +void __no_sanitize_address arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
> +					   struct task_struct *task, struct pt_regs *regs)
> +{
> +	unsigned long sp;
> +
> +	if (regs && !consume_entry(cookie, regs->pc))
> +		return;
> +
> +	if (regs)
> +		sp = (unsigned long) regs;
> +	else if (task == current)
> +		sp = current_stack_frame();
> +	else
> +		sp = task->thread.ksp;
> +
> +	for (;;) {
> +		unsigned long *stack = (unsigned long *) sp;
> +		unsigned long newsp, ip;
> +
> +		if (!validate_sp(sp, task))
> +			return;
> +
> +		newsp = stack[0];
> +		ip = stack[1];
> +
> +		if (!consume_entry(cookie, ip))
> +			return;
> +
> +		sp = newsp;
> +	}
> +}
>