Unlike perf callchain relying on walk_stackframe(), dump_backtrace()
has its own backtrace logic. A major difference between them is the
moment a symbol is recorded. Perf writes down a symobl *before*
calling unwind_frame(), but dump_backtrace() prints it out *after*
unwind_frame(). As a result, the last valid symbol cannot be hooked
in case of dump_backtrace(). This patch addresses the issue as
synchronising dump_backtrace() with perf callchain.
A simple test and its results are as follows:
- crash trigger
$ sudo echo c > /proc/sysrq-trigger
- current status
Call trace:
[<fffffe00003dc738>] sysrq_handle_crash+0x24/0x30
[<fffffe00003dd2ac>] __handle_sysrq+0x128/0x19c
[<fffffe00003dd730>] write_sysrq_trigger+0x60/0x74
[<fffffe0000249fc4>] proc_reg_write+0x84/0xc0
[<fffffe00001f2638>] __vfs_write+0x44/0x104
[<fffffe00001f2e60>] vfs_write+0x98/0x1a8
[<fffffe00001fe730>] SyS_write+0x50/0xb0
- with this change
Call trace:
[<fffffe00003dc738>] sysrq_handle_crash+0x24/0x30
[<fffffe00003dd2ac>] __handle_sysrq+0x128/0x19c
[<fffffe00003dd730>] write_sysrq_trigger+0x60/0x74
[<fffffe0000249fc4>] proc_reg_write+0x84/0xc0
[<fffffe00001f2638>] __vfs_write+0x44/0x104
[<fffffe00001f2e60>] vfs_write+0x98/0x1a8
[<fffffe00001fe730>] SyS_write+0x50/0xb0
[<fffffe00000939ec>] el0_svc_naked+0x20/0x28
Note that this patch does not cover a case where MMU is disabled. The
last stack frame of swapper, for example, has PC in a form of physical
address. Unfortunately, a simple conversion using phys_to_virt() cannot
cover all scenarios since PC is retrieved from LR - 4, not LR. It is
a big tradeoff to change both head.S and unwind_frame() for only a few
of symbols in *.S. Thus, this hunk does not take care of the case.
Cc: AKASHI Takahiro <takahiro.aka...@linaro.org>
Cc: James Morse <james.mo...@arm.com>
Cc: Mark Rutland <mark.rutl...@arm.com>
Signed-off-by: Jungseok Lee <jungseokle...@gmail.com>
---
Changes since v1:
- Added an example to the commit msg, per Will
- Modified a comment.
arch/arm64/kernel/traps.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index f93aae5..e9b9b53 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -103,12 +103,12 @@ static void dump_mem(const char *lvl, const char *str,
unsigned long bottom,
set_fs(fs);
}
-static void dump_backtrace_entry(unsigned long where, unsigned long stack)
+static void dump_backtrace_entry(unsigned long where)
{
+ /*
+ * Note that 'where' can have a physical address, but it's not handled.
+ */
print_ip_sym(where);
- if (in_exception_text(where))
- dump_mem("", "Exception stack", stack,
- stack + sizeof(struct pt_regs), false);
}
static void dump_instr(const char *lvl, struct pt_regs *regs)
@@ -172,12 +172,17 @@ static void dump_backtrace(struct pt_regs *regs, struct
task_struct *tsk)
pr_emerg("Call trace:\n");
while (1) {
unsigned long where = frame.pc;
+ unsigned long stack;
int ret;
+ dump_backtrace_entry(where);
ret = unwind_frame(&frame);
if (ret < 0)
break;
- dump_backtrace_entry(where, frame.sp);
+ stack = frame.sp;
+ if (in_exception_text(where))
+ dump_mem("", "Exception stack", stack,
+ stack + sizeof(struct pt_regs), false);
}
}
--
2.5.0
--
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