[PATCH v4 0/2] Add basic tracing support for m68k

[PATCH v4 0/2] Add basic tracing support for m68k

[Jean-Michel Hautbois]

In order to debug latency issues, I wanted to use ftrace on my M54418
coldfire. Sadly, it is not supported yet.
Thanks to Steven [1] it does not sound too difficult.

This small series adds basic functions to make it work, and for the few
tests I could do, it seems to be working well.

Here is a simple output I get:

```

            bash-232     [000] d..3.   947.629000: thread_noise:     bash:232 start 947.629000000 duration 0 ns
      timerlat/0-274     [000] .....   947.629000: #51598 context thread timer_latency    409280 ns
            bash-232     [000] d.h..   947.630000: #51599 context    irq timer_latency    110720 ns
            bash-232     [000] dnh1.   947.630000: irq_noise: timer:206 start 947.629000000 duration 1000000 ns
            bash-232     [000] d..3.   947.630000: thread_noise:     bash:232 start 947.630000000 duration 0 ns
      timerlat/0-274     [000] .....   947.630000: #51599 context thread timer_latency    407168 ns
            bash-232     [000] d.h..   947.631000: #51600 context    irq timer_latency    108608 ns
            bash-232     [000] dnh1.   947.631000: irq_noise: timer:206 start 947.630000000 duration 1000000 ns
            bash-232     [000] d..3.   947.631000: thread_noise:     bash:232 start 947.631000000 duration 0 ns
      timerlat/0-274     [000] .....   947.631000: #51600 context thread timer_latency    401472 ns
```

I used this on my board and afaik, it works quite well.

```

 telnetd-229       0Dnh4.   13us+:      229:120:R   + [000]     118: 49:R irq/100-enet-fe
 telnetd-229       0Dnh4.   53us+: <stack trace>
 => __trace_stack
 => probe_wakeup
 => try_to_wake_up
 => wake_up_process
 => __handle_irq_event_percpu
 => handle_irq_event
 => handle_level_irq
 => generic_handle_irq
 => do_IRQ
 => inthandler
 => ip_finish_output2
 => __ip_finish_output
 => ip_output
 => __ip_queue_xmit
 => ip_queue_xmit
 => __tcp_transmit_skb
 => tcp_write_xmit
 => __tcp_push_pending_frames
 => tcp_push
 => tcp_sendmsg_locked
 => tcp_sendmsg
 => inet_sendmsg
 => sock_write_iter
 => vfs_write
 => ksys_write
 => sys_write
 => system_call
 telnetd-229       0Dnh4.   68us!: wake_up_process <-__handle_irq_event_percpu
 telnetd-229       0D..3.  348us+: __schedule <-preempt_schedule_irq
 telnetd-229       0D..3.  368us+:      229:120:R ==> [000]     118: 49:R irq/100-enet-fe
 telnetd-229       0D..3.  395us : <stack trace>
 => __trace_stack
 => probe_wakeup_sched_switch
 => __schedule
 => preempt_schedule_irq
 => Lkernel_return
 => ip_finish_output2
 => __ip_finish_output
 => ip_output
 => __ip_queue_xmit
 => ip_queue_xmit
 => __tcp_transmit_skb
 => tcp_write_xmit
 => __tcp_push_pending_frames
 => tcp_push
 => tcp_sendmsg_locked
 => tcp_sendmsg
 => inet_sendmsg
 => sock_write_iter
 => vfs_write
 => ksys_write
 => sys_write
 => system_call
```

[1]: https://lore.kernel.org/linux-m68k/20241018124511.70d29198@gandalf.local.home

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
---
Changes in v4:
- Take Steve's v1 remarks !
- Link to v3: https://lore.kernel.org/r/20241203-add-m68k-tracing-support-v3-0-4de93f6cae55@yoseli.org

Changes in v3:
- Do not unconditionaly select the frame pointers
- Link to v2: https://lore.kernel.org/r/20241203-add-m68k-tracing-support-v2-0-77302097a9f4@yoseli.org

Changes in v2:
- Use the frame pointer and declare it
- Comments on trace_irq have been tested, but adding the trace_on/off in
  entry.S fails badly
- Link to v1: https://lore.kernel.org/r/20241021-add-m68k-tracing-support-v1-0-0883d704525b@yoseli.org

---
Jean-Michel Hautbois (2):
      m68k: Enable traceirqs
      arch: m68k: Add STACKTRACE support

 arch/m68k/Kconfig             |  6 ++++
 arch/m68k/kernel/Makefile     |  1 +
 arch/m68k/kernel/stacktrace.c | 70 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)
---
base-commit: e70140ba0d2b1a30467d4af6bcfe761327b9ec95
change-id: 20241021-add-m68k-tracing-support-36c18d2233d8

Best regards,
-- 
Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>

[PATCH v4 1/2] m68k: Enable traceirqs

[Jean-Michel Hautbois]

As irq_enter() and irq_exit() already are tracing the state, we can
safely enable TRACE_IRQFLAGS_SUPPORT.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
---
 arch/m68k/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 7c4f7bcc89d76326b9d7280a3bcba79412ead7d2..793ab1e2762609725bbf793f6dffecfa3ecfff0f 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -39,6 +39,7 @@ config M68K
 	select OLD_SIGSUSPEND3
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA
+	select TRACE_IRQFLAGS_SUPPORT
 
 config CPU_BIG_ENDIAN
 	def_bool y

-- 
2.39.5

[PATCH v4 2/2] arch: m68k: Add STACKTRACE support

[Jean-Michel Hautbois]

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@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 793ab1e2762609725bbf793f6dffecfa3ecfff0f..3ad8596aab71190807f8c11dd5876aa1198760f3 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -106,6 +106,11 @@ 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
+	def_bool MMU_COLDFIRE
+	select ARCH_STACKWALK
+	select ARCH_WANT_FRAME_POINTERS
+
 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;
+	}
+}

-- 
2.39.5

Re: [PATCH v4 2/2] arch: m68k: Add STACKTRACE support

[Greg Ungerer]

Hi JM,

On 4/12/24 17:14, 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@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 793ab1e2762609725bbf793f6dffecfa3ecfff0f..3ad8596aab71190807f8c11dd5876aa1198760f3 100644
> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -106,6 +106,11 @@ 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
> +	def_bool MMU_COLDFIRE

Modulo testing is there any reason this is enabled only for MMU ColdFire targets?
There doesn't look to be anything that is ColdFire specific in these changes,
looks like it should work on any m68k machine.

Regards
Greg



> +	select ARCH_STACKWALK
> +	select ARCH_WANT_FRAME_POINTERS
> +
>   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;
> +	}
> +}
> 

Re: [PATCH v4 2/2] arch: m68k: Add STACKTRACE support

[Jean-Michel Hautbois]

Hi Greg,

On 22/12/2024 14:14, Greg Ungerer wrote:
> Hi JM,
> 
> On 4/12/24 17:14, 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@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 
>> 793ab1e2762609725bbf793f6dffecfa3ecfff0f..3ad8596aab71190807f8c11dd5876aa1198760f3 100644
>> --- a/arch/m68k/Kconfig
>> +++ b/arch/m68k/Kconfig
>> @@ -106,6 +106,11 @@ 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
>> +    def_bool MMU_COLDFIRE
> 
> Modulo testing is there any reason this is enabled only for MMU ColdFire 
> targets?

You said it, modulo testing (and lack of knowledge on my side to be 
certain it is not coldfire specific) :-).

If it can be tested on other machines, I would be glad to change it !

Thanks,
JM

> There doesn't look to be anything that is ColdFire specific in these 
> changes,
> looks like it should work on any m68k machine.
> 
> Regards
> Greg
> 
> 
> 
>> +    select ARCH_STACKWALK
>> +    select ARCH_WANT_FRAME_POINTERS
>> +
>>   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;
>> +    }
>> +}
>>
>