Re: [PATCH RFC 2/2] arch: m68k: Add STACKTRACE support

[Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>]

Hi there,

On 21/10/2024 11:44, 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.

Well, I said it was tested, but it was only compile tested basically.
AFAICT now, I think it is not working as when I use wakeup_rt as a 
tracer, I don't have the stack trace:

# wakeup_rt latency trace v1.1.5 on 6.12.0-10380-gb66f06337b66-dirty
# --------------------------------------------------------------------
# latency: 2000 us, #18/18, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
#    -----------------
#    | task: irq/100-enet-fe-118 (uid:0 nice:0 policy:1 rt_prio:50)
#    -----------------
#
#                    _------=> CPU#
#                   / _-----=> irqs-off/BH-disabled
#                  | / _----=> need-resched
#                  || / _---=> hardirq/softirq
#                  ||| / _--=> preempt-depth
#                  |||| / _-=> migrate-disable
#                  ||||| /     delay
#  cmd     pid     |||||| time  |   caller
#     \   /        ||||||  \    |    /
kworker/-11        0dnh5.    0us :       11:120:R   + [000]      22: 
98:R irq_work/0
kworker/-11        0dnh5.    0us : <stack trace>
kworker/-11        0dnh5.    0us : 0
kworker/-11        0d..3.    0us : __schedule
kworker/-11        0d..3.    0us :       11:120:R ==> [000]      22: 
98:R irq_work/0
kworker/-11        0d..3.    0us : <stack trace>
  telnetd-229       0Dnh4.    0us :      229:120:R   + [000]     118: 
49:R irq/100-enet-fe
  telnetd-229       0Dnh4.    0us : <stack trace>
  telnetd-229       0Dnh4.    0us : 0
  telnetd-229       0D..3.    0us : __schedule
  telnetd-229       0D..3.    0us :      229:120:R ==> [000]     118: 
49:R irq/100-enet-fe
  telnetd-229       0D..3.    0us : <stack trace>
  telnetd-229       0dn.5.    0us :      229:120:R   + [000]     118: 
49:R irq/100-enet-fe
  telnetd-229       0dn.5.    0us : <stack trace>
  telnetd-229       0dn.5.    0us#: 0
  telnetd-229       0d..3. 2000us : __schedule
  telnetd-229       0d..3. 2000us :      229:120:R ==> [000]     118: 
49:R irq/100-enet-fe
  telnetd-229       0d..3. 2000us : <stack trace>

Geert, Greg, and maybe other highly skilled m68k people, could you 
please help me with this particular function :-) ?

Thanks !
JM

> 
> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
> ---
>   arch/m68k/Kconfig             |  5 ++++
>   arch/m68k/kernel/Makefile     |  1 +
>   arch/m68k/kernel/stacktrace.c | 70 +++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 76 insertions(+)
> 
> diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
> index ab3375475721fa63418c40d4ba6ac76679ebc77d..7142f9759181a90269ae1ba9e682d331ee2ddbf6 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -40,6 +40,7 @@ config M68K
>   	select UACCESS_MEMCPY if !MMU
>   	select ZONE_DMA
>   	select TRACE_IRQFLAGS_SUPPORT
> +	select ARCH_STACKWALK
>   
>   config CPU_BIG_ENDIAN
>   	def_bool y
> @@ -107,6 +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
> +
>   menu "Platform setup"
>   
>   source "arch/m68k/Kconfig.cpu"
> diff --git a/arch/m68k/kernel/Makefile b/arch/m68k/kernel/Makefile
> index f335bf3268a108a45bab079fbf0a1c8ead9beb71..4efe92af0b711b19cb1d5129f74e67a739e289b1 100644
> --- a/arch/m68k/kernel/Makefile
> +++ b/arch/m68k/kernel/Makefile
> @@ -31,3 +31,4 @@ 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..06c7459373bd25b3bb3540cfe2a909259c1db3ce
> --- /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 %%sp, %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;
> +	}
> +}
>