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ftrace: Add MODIFIED flag to show if IPMODIFY or direct was attached 

If a function had ever had IPMODIFY or DIRECT attached to it, where this
is how live kernel patching and BPF overrides work, mark them and display
an "M" in the enabled_functions and touched_functions files. This can be
used for debugging. If a function had been modified and later there's a bug
in the code related to that function, this can be used to know if the cause
is possibly from a live kernel patch or a BPF program that changed the
behavior of the code.

Also update the documentation on the enabled_functions and
touched_functions output, as it was missing direct callers and CALL_OPS.
And include this new modify attribute.

Link: https://lore.kernel.org/linux-trace-kernel/20230502213233.004e3ae4@gandalf.local.home

Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Google) 2023-05-02 21:32:33 -04:00
parent 4f94559f40
commit 6ce2c04fcb
3 changed files with 37 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
Documentation/trace/ftrace.rst
View File

@ -350,6 +350,19 @@ of ftrace. Here is a list of some of the key files:
an 'I' will be displayed on the same line as the function that
can be overridden.
If a non ftrace trampoline is attached (BPF) a 'D' will be displayed.
Note, normal ftrace trampolines can also be attached, but only one
"direct" trampoline can be attached to a given function at a time.
Some architectures can not call direct trampolines, but instead have
the ftrace ops function located above the function entry point. In
such cases an 'O' will be displayed.
If a function had either the "ip modify" or a "direct" call attached to
it in the past, a 'M' will be shown. This flag is never cleared. It is
used to know if a function was every modified by the ftrace infrastructure,
and can be used for debugging.
If the architecture supports it, it will also show what callback
is being directly called by the function. If the count is greater
than 1 it most likely will be ftrace_ops_list_func().
@ -359,6 +372,18 @@ of ftrace. Here is a list of some of the key files:
its address will be printed as well as the function that the
trampoline calls.
touched_functions:
This file contains all the functions that ever had a function callback
to it via the ftrace infrastructure. It has the same format as
enabled_functions but shows all functions that have every been
traced.
To see any function that has every been modified by "ip modify" or a
direct trampoline, one can perform the following command:
grep ' M ' /sys/kernel/tracing/touched_functions
function_profile_enabled:
When set it will enable all functions with either the function

4
include/linux/ftrace.h
View File

@ -549,6 +549,7 @@ bool is_ftrace_trampoline(unsigned long addr);
* CALL_OPS - the record can use callsite-specific ops
* CALL_OPS_EN - the function is set up to use callsite-specific ops
* TOUCHED - A callback was added since boot up
* MODIFIED - The function had IPMODIFY or DIRECT attached to it
*
* When a new ftrace_ops is registered and wants a function to save
* pt_regs, the rec->flags REGS is set. When the function has been
@ -569,9 +570,10 @@ enum {
FTRACE_FL_CALL_OPS = (1UL << 22),
FTRACE_FL_CALL_OPS_EN = (1UL << 21),
FTRACE_FL_TOUCHED = (1UL << 20),
FTRACE_FL_MODIFIED = (1UL << 19),
};
#define FTRACE_REF_MAX_SHIFT 20
#define FTRACE_REF_MAX_SHIFT 19
#define FTRACE_REF_MAX ((1UL << FTRACE_REF_MAX_SHIFT) - 1)
#define ftrace_rec_count(rec) ((rec)->flags & FTRACE_REF_MAX)

12
kernel/trace/ftrace.c
View File

@ -46,7 +46,8 @@
#include "trace_stat.h"
/* Flags that do not get reset */
#define FTRACE_NOCLEAR_FLAGS (FTRACE_FL_DISABLED | FTRACE_FL_TOUCHED)
#define FTRACE_NOCLEAR_FLAGS (FTRACE_FL_DISABLED | FTRACE_FL_TOUCHED | \
FTRACE_FL_MODIFIED)
#define FTRACE_INVALID_FUNCTION "__ftrace_invalid_address__"
@ -2273,6 +2274,10 @@ static int ftrace_check_record(struct dyn_ftrace *rec, bool enable, bool update)
rec->flags &= ~FTRACE_FL_TRAMP_EN;
}
/* Keep track of anything that modifies the function */
if (rec->flags & (FTRACE_FL_DIRECT | FTRACE_FL_IPMODIFY))
rec->flags |= FTRACE_FL_MODIFIED;
if (flag & FTRACE_FL_DIRECT) {
/*
* If there's only one user (direct_ops helper)
@ -3866,12 +3871,13 @@ static int t_show(struct seq_file *m, void *v)
if (iter->flags & (FTRACE_ITER_ENABLED | FTRACE_ITER_TOUCHED)) {
struct ftrace_ops *ops;
seq_printf(m, " (%ld)%s%s%s%s",
seq_printf(m, " (%ld)%s%s%s%s%s",
ftrace_rec_count(rec),
rec->flags & FTRACE_FL_REGS ? " R" : " ",
rec->flags & FTRACE_FL_IPMODIFY ? " I" : " ",
rec->flags & FTRACE_FL_DIRECT ? " D" : " ",
rec->flags & FTRACE_FL_CALL_OPS ? " O" : " ");
rec->flags & FTRACE_FL_CALL_OPS ? " O" : " ",
rec->flags & FTRACE_FL_MODIFIED ? " M " : " ");
if (rec->flags & FTRACE_FL_TRAMP_EN) {
ops = ftrace_find_tramp_ops_any(rec);
if (ops) {