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

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Message-ID: <b20a80d4-2539-4771-897e-f8339a09545b@yoseli.org>
Date: Tue, 3 Dec 2024 20:10:21 +0100
From: Jean-Michel Hautbois <jeanmichel.hautbois@...eli.org>
To: Michael Schmitz <schmitzmic@...il.com>,
 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

Hi Michael,

On 03/12/2024 19:21, Michael Schmitz wrote:
> Jean-Michel,
> 
> good work on adding

Thanks ^_^

> 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) ...

Oh yeah, I have such a fast (ah ah) cpu that I forget others may not.
I have not measure the size it adds.

> 
> 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?

Absolutely not, I will add those here and condition the stacktrace to 
coldfire (or even M5441x ?) ?

>>   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;
>> +    }
>> +}
>>