Re: [PATCH RFC 2/2] arch: m68k: Add STACKTRACE support
From: Jean-Michel Hautbois
Date: Mon Dec 02 2024 - 12:53:36 EST
Hi Greg,
On 02/12/2024 15:41, Greg Ungerer wrote:
Hi JM,
On 27/11/24 21:26, Jean-Michel Hautbois wrote:
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@xxxxxxxxxx>
---
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;
+}
If I am understanding what this is intended to do then this is probably
not right.
This will be returning the current stack pointer, which will almost
certainly not
be the current stack frame pointer. This will be the top of stack at the
call site,
which will be after the pushed locals and saved registers at the very
least for m68k.
Does your kernel config have CONFIG_FRAME_POINTER enabled?
The default for m68k is usually disabled. Without this there won't be a
chain of frame pointers to follow like the code is trying to do below in
arch_stack_walk().
It gives me a few things when I use wakeup_rt but timerlat is not giving
me any stack:
# cd /sys/kernel/debug/tracing/
# echo 500 > osnoise/stop_tracing_total_us
# echo 500 > osnoise/print_stack
# echo timerlat > current_tracer
# echo 1 > tracing_on
# tail -21 trace
# tail -21 trace
timerlat/0-299 [000] ..... 635.167643: #59035 context
thread timer_latency 202352 ns
kworker/u5:1-242 [000] d.h1. 635.168494: #59036 context
irq timer_latency 51504 ns
timerlat/0-299 [000] ..... 635.168714: #59036 context
thread timer_latency 272032 ns
bash-230 [000] d.h.. 635.169496: #59037 context
irq timer_latency 54592 ns
timerlat/0-299 [000] ..... 635.169693: #59037 context
thread timer_latency 250448 ns
bash-230 [000] d.h.. 635.170491: #59038 context
irq timer_latency 48784 ns
timerlat/0-299 [000] ..... 635.170717: #59038 context
thread timer_latency 275960 ns
bash-230 [000] d.h.. 635.171497: #59039 context
irq timer_latency 54472 ns
timerlat/0-299 [000] ..... 635.171695: #59039 context
thread timer_latency 252936 ns
bash-230 [000] d.h1. 635.172495: #59040 context
irq timer_latency 53064 ns
timerlat/0-299 [000] ..... 635.172696: #59040 context
thread timer_latency 253144 ns
bash-230 [000] d.h1. 635.173491: #59041 context
irq timer_latency 49864 ns
timerlat/0-299 [000] ..... 635.173683: #59041 context
thread timer_latency 241248 ns
bash-230 [000] d.h1. 635.174495: #59042 context
irq timer_latency 52648 ns
timerlat/0-299 [000] ..... 635.174691: #59042 context
thread timer_latency 249216 ns
bash-230 [000] d.h.. 635.175536: #59043 context
irq timer_latency 94496 ns
timerlat/0-299 [000] ..... 635.175762: #59043 context
thread timer_latency 321592 ns
bash-324 [000] d.h.. 635.176825: #59044 context
irq timer_latency 383560 ns
timerlat/0-299 [000] ..... 635.177044: #59044 context
thread timer_latency 603280 ns
timerlat/0-299 [000] ...1. 635.177091: <stack trace>
timerlat/0-299 [000] ..... 635.177141: timerlat_main: stop
tracing hit on cpu 0
As you can see, stack_trace appears, but nothing is displayed so I
suppose it does not walk at all...
Thanks,
JM