Re: [PATCH v2] ftrace: Fix function name for trampoline

[t s]

On 2024/10/19 0:22, Steven Rostedt wrote:

On Sat, 12 Oct 2024 21:41:51 +0900
Tatsuya S <tatsuya.s2...@gmail.com> wrote:

The issue that unrelated function name is shown on stack trace like
following even though it should be trampoline code address is caused by
the creation of trampoline code in the area where .init.text section
of module was freed after module is loaded.

bash-1344    [002] .....    43.644608: <stack trace>
   => (MODULE INIT FUNCTION)
   => vfs_write
   => ksys_write
   => do_syscall_64
   => entry_SYSCALL_64_after_hwframe

To resolve this, when function address of stack trace entry is in
trampoline, output without looking up symbol name.

Signed-off-by: Tatsuya S <tatsuya.s2...@gmail.com>
---
V1 -> V2: Instead of checking trampoline when displaying "trace" results,
          it stores trampoline when generating the stacktrace entry.

Thank you for review.

I'm sorry. I guess I wasn't clear. I meant to do the tests in the recording
of the trampoline, and do not add them or replace them. I rather not add
this meta data to the ring buffer.

  kernel/trace/trace.c         | 24 ++++++++++++++++--------
  kernel/trace/trace_entries.h |  2 ++
  kernel/trace/trace_output.c  |  7 +++++++
  3 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1c69ca1f1088..92a8e76a0cd7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -988,7 +988,8 @@ static inline void trace_access_lock_init(void)
  #endif

#ifdef CONFIG_STACKTRACE

-static void __ftrace_trace_stack(struct trace_buffer *buffer,
+static void __ftrace_trace_stack(struct trace_array *tr,
+                                struct trace_buffer *buffer,
                                 unsigned int trace_ctx,
                                 int skip, struct pt_regs *regs);
  static inline void ftrace_trace_stack(struct trace_array *tr,
@@ -997,7 +998,8 @@ static inline void ftrace_trace_stack(struct trace_array 
*tr,
                                      int skip, struct pt_regs *regs);

#else

-static inline void __ftrace_trace_stack(struct trace_buffer *buffer,
+static inline void __ftrace_trace_stack(struct trace_array *tr,
+                                       struct trace_buffer *buffer,
                                        unsigned int trace_ctx,
                                        int skip, struct pt_regs *regs)
  {
@@ -2928,7 +2930,8 @@ struct ftrace_stacks {
  static DEFINE_PER_CPU(struct ftrace_stacks, ftrace_stacks);
  static DEFINE_PER_CPU(int, ftrace_stack_reserve);

-static void __ftrace_trace_stack(struct trace_buffer *buffer,

+static void __ftrace_trace_stack(struct trace_array *tr,
+                                struct trace_buffer *buffer,
                                 unsigned int trace_ctx,
                                 int skip, struct pt_regs *regs)
  {
@@ -2986,6 +2989,11 @@ static void __ftrace_trace_stack(struct trace_buffer 
*buffer,
        memcpy(&entry->caller, fstack->calls,
               flex_array_size(entry, caller, nr_entries));

+#ifdef CONFIG_DYNAMIC_FTRACE

+       entry->trampoline = tr->ops ? tr->ops->trampoline : 0;
+       entry->trampoline_size = tr->ops ? tr->ops->trampoline_size : 0;
+#endif
+
        if (!call_filter_check_discard(call, entry, buffer, event))
                __buffer_unlock_commit(buffer, event);

I meant here we can add something like:

/* Make the marker not exactly -1, but max int to be something somewhat unique 
*/
#define FTRACE_TRAMPOLINE_MARKER        ((unsigned long)MAX_INT)


        if (regs) {
                nr_entries = stack_trace_save_regs(regs, fstack->calls,
                                                   size, skip);
        } else {
                nr_entries = stack_trace_save(fstack->calls, size, skip);
        }

+       if (tr->ops && tr->ops->trampoline) {
+               unsigned long tramp_start = tr->ops->trampoline;
+               unsigned long tramp_end = tramp_start + 
tr->ops->trampoline_size;
+               unsigned long *calls = fstack->calls;
+
+               /* Mark any trampolines */
+               for (int i = 0; i < nr_entries; i++) {
+                       if (calls[i] >= tramp_start && calls[i] < tramp_end) {
+                               calls[i] = FTRACE_TRAMPOLINE_MARKER;
+               }
+       }
+
        event = __trace_buffer_lock_reserve(buffer, TRACE_STACK,
                                    struct_size(entry, caller, nr_entries),
                                    trace_ctx);
        if (!event)
                goto out;
        entry = ring_buffer_event_data(event);

        entry->size = nr_entries;
        memcpy(&entry->caller, fstack->calls,
               flex_array_size(entry, caller, nr_entries));

@@ -3005,7 +3013,7 @@ static inline void ftrace_trace_stack(struct trace_array 
*tr,
        if (!(tr->trace_flags & TRACE_ITER_STACKTRACE))
                return;

- __ftrace_trace_stack(buffer, trace_ctx, skip, regs);

+       __ftrace_trace_stack(tr, buffer, trace_ctx, skip, regs);
  }

void __trace_stack(struct trace_array *tr, unsigned int trace_ctx,

@@ -3014,7 +3022,7 @@ void __trace_stack(struct trace_array *tr, unsigned int 
trace_ctx,
        struct trace_buffer *buffer = tr->array_buffer.buffer;

if (rcu_is_watching()) {

-               __ftrace_trace_stack(buffer, trace_ctx, skip, NULL);
+               __ftrace_trace_stack(tr, buffer, trace_ctx, skip, NULL);
                return;
        }

@@ -3031,7 +3039,7 @@ void __trace_stack(struct trace_array *tr, unsigned int trace_ctx,

                return;

ct_irq_enter_irqson();

-       __ftrace_trace_stack(buffer, trace_ctx, skip, NULL);
+       __ftrace_trace_stack(tr, buffer, trace_ctx, skip, NULL);
        ct_irq_exit_irqson();
  }

@@ -3048,8 +3056,8 @@ void trace_dump_stack(int skip)

        /* Skip 1 to skip this function. */
        skip++;
  #endif
-       __ftrace_trace_stack(printk_trace->array_buffer.buffer,
-                            tracing_gen_ctx(), skip, NULL);
+       __ftrace_trace_stack(printk_trace, printk_trace->array_buffer.buffer,
+                               tracing_gen_ctx(), skip, NULL);
  }
  EXPORT_SYMBOL_GPL(trace_dump_stack);

diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h

index c47422b20908..81b84241e3b3 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -190,6 +190,8 @@ FTRACE_ENTRY(kernel_stack, stack_entry,

F_STRUCT(

                __field(        int,            size    )
+               __field(        unsigned long,  trampoline      )
+               __field(        unsigned long,  trampoline_size )
                __stack_array(  unsigned long,  caller, FTRACE_STACK_ENTRIES, 
size)
        ),

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c

index 868f2f912f28..fbd066e9c9fa 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1246,6 +1246,13 @@ static enum print_line_t trace_stack_print(struct 
trace_iterator *iter,
                        break;

trace_seq_puts(s, " => ");

+               if (field->trampoline && field->trampoline_size &&
+                       (*p) + delta >= field->trampoline &&
+                       (*p) + delta < field->trampoline + 
field->trampoline_size) {

Then the above can simply be:

                if ((*p) == FTRACE_TRAMPOLINE_MARKER) {
                        trace_seq_puts(s, "[FTRACE TRAMPOLINE]\n");
                        continue;
                }

since the value is useless anyway.

-- Steve

OK.


Thanks.

+                       trace_seq_printf(s, "0x%08lx", (*p) + delta);
+                       trace_seq_puts(s, " [FTRACE TRAMPOLINE]\n");
+                       continue;
+               }
                seq_print_ip_sym(s, (*p) + delta, flags);
                trace_seq_putc(s, '\n');
        }