[PATCH v2 0/2] Add basic tracing support for m68k

[PATCH v2 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 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: Add tracirqs
      arch: m68k: Add STACKTRACE support

 arch/m68k/Kconfig             |  7 +++++
 arch/m68k/kernel/Makefile     |  1 +
 arch/m68k/kernel/irq.c        |  2 ++
 arch/m68k/kernel/stacktrace.c | 70 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 80 insertions(+)
---
base-commit: e70140ba0d2b1a30467d4af6bcfe761327b9ec95
change-id: 20241021-add-m68k-tracing-support-36c18d2233d8

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

[PATCH v2 1/2] m68k: Add tracirqs

[Jean-Michel Hautbois]

The TRACE_IRQFLAGS_SUPPORT requires the architecture to call
trace_hardirqs_off() when interrupts are disabled and
trace_hardirqs_on() when they are enabled.
Add those calls to do_IRQ function.

Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
---
 arch/m68k/Kconfig      | 1 +
 arch/m68k/kernel/irq.c | 2 ++
 2 files changed, 3 insertions(+)

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
diff --git a/arch/m68k/kernel/irq.c b/arch/m68k/kernel/irq.c
index 9ab4f550342e5de11c528f55781432675ffd66bf..74cf60ebbc4bca51f3caa4046dbd2bdb02355711 100644
--- a/arch/m68k/kernel/irq.c
+++ b/arch/m68k/kernel/irq.c
@@ -21,9 +21,11 @@ asmlinkage void do_IRQ(int irq, struct pt_regs *regs)
 {
 	struct pt_regs *oldregs = set_irq_regs(regs);
 
+	trace_hardirqs_off();
 	irq_enter();
 	generic_handle_irq(irq);
 	irq_exit();
+	trace_hardirqs_on();
 
 	set_irq_regs(oldregs);
 }

-- 
2.39.5

[PATCH v2 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             |  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
 
 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
+
 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 v2 2/2] arch: m68k: Add STACKTRACE support

[Michael Schmitz]

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@yoseli.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;
> +	}
> +}
>

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

[Jean-Michel Hautbois]

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@yoseli.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;
>> +    }
>> +}
>>