diff mbox series

[RFC,v2,1/4] tracing: add __print_sym() to replace __print_symbolic()

Message ID 20240326202131.9d261d5bb667.I9bd2617499f0d170df58471bc51379742190f92d@changeid (mailing list archive)
State RFC
Delegated to: Johannes Berg
Headers show
Series tracing: improve symbolic printing | expand

Commit Message

Johannes Berg March 26, 2024, 7:15 p.m. UTC
From: Johannes Berg <johannes.berg@intel.com>

The way __print_symbolic() works is limited and inefficient
in multiple ways:
 - you can only use it with a static list of symbols, but
   e.g. the SKB dropreasons are now a dynamic list

 - it builds the list in memory _three_ times, so it takes
   a lot of memory:
   - The print_fmt contains the list (since it's passed to
     the macro there). This actually contains the names
     _twice_, which is fixed up at runtime.
   - TRACE_DEFINE_ENUM() puts a 24-byte struct trace_eval_map
     for every entry, plus the string pointed to by it, which
     cannot be deduplicated with the strings in the print_fmt
   - The in-kernel symbolic printing creates yet another list
     of struct trace_print_flags for trace_print_symbols_seq()

 - it also requires runtime fixup during init, which is a lot
   of string parsing due to the print_fmt fixup

Introduce __print_sym() to - over time - replace the old one.
We can easily extend this also to __print_flags later, but I
cared only about the SKB dropreasons for now, which has only
__print_symbolic().

This new __print_sym() requires only a single list of items,
created by TRACE_DEFINE_SYM_LIST(), or can even use another
already existing list by using TRACE_DEFINE_SYM_FNS() with
lookup and show methods.

Then, instead of doing an init-time fixup, just do this at the
time when userspace reads the print_fmt. This way, dynamically
updated lists are possible.

For userspace, nothing actually changes, because the print_fmt
is shown exactly the same way the old __print_symbolic() was.

This adds about 4k .text in my test builds, but that'll be
more than paid for by the actual conversions.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2:
 - fix RCU
 - use ':' as separator to simplify the code, that's
   still not valid in a C identifier
---
 include/asm-generic/vmlinux.lds.h          |  3 +-
 include/linux/module.h                     |  2 +
 include/linux/trace_events.h               |  7 ++
 include/linux/tracepoint.h                 | 20 +++++
 include/trace/stages/init.h                | 54 +++++++++++++
 include/trace/stages/stage2_data_offsets.h |  6 ++
 include/trace/stages/stage3_trace_output.h |  9 +++
 include/trace/stages/stage7_class_define.h |  3 +
 kernel/module/main.c                       |  3 +
 kernel/trace/trace_events.c                | 90 +++++++++++++++++++++-
 kernel/trace/trace_output.c                | 45 +++++++++++
 11 files changed, 239 insertions(+), 3 deletions(-)

Comments

Simon Horman March 27, 2024, 9:11 p.m. UTC | #1
On Tue, Mar 26, 2024 at 08:15:56PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> The way __print_symbolic() works is limited and inefficient
> in multiple ways:
>  - you can only use it with a static list of symbols, but
>    e.g. the SKB dropreasons are now a dynamic list
> 
>  - it builds the list in memory _three_ times, so it takes
>    a lot of memory:
>    - The print_fmt contains the list (since it's passed to
>      the macro there). This actually contains the names
>      _twice_, which is fixed up at runtime.
>    - TRACE_DEFINE_ENUM() puts a 24-byte struct trace_eval_map
>      for every entry, plus the string pointed to by it, which
>      cannot be deduplicated with the strings in the print_fmt
>    - The in-kernel symbolic printing creates yet another list
>      of struct trace_print_flags for trace_print_symbols_seq()
> 
>  - it also requires runtime fixup during init, which is a lot
>    of string parsing due to the print_fmt fixup
> 
> Introduce __print_sym() to - over time - replace the old one.
> We can easily extend this also to __print_flags later, but I
> cared only about the SKB dropreasons for now, which has only
> __print_symbolic().
> 
> This new __print_sym() requires only a single list of items,
> created by TRACE_DEFINE_SYM_LIST(), or can even use another
> already existing list by using TRACE_DEFINE_SYM_FNS() with
> lookup and show methods.
> 
> Then, instead of doing an init-time fixup, just do this at the
> time when userspace reads the print_fmt. This way, dynamically
> updated lists are possible.
> 
> For userspace, nothing actually changes, because the print_fmt
> is shown exactly the same way the old __print_symbolic() was.
> 
> This adds about 4k .text in my test builds, but that'll be
> more than paid for by the actual conversions.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Hi Johannes,

I'm seeing some allmodconfig build problems with this applied on top of
net-next.

In file included from ./include/trace/trace_events.h:27,
                 from ./include/trace/define_trace.h:102,
                 from ./include/trace/events/module.h:134,
                 from kernel/module/main.c:64:
./include/trace/stages/init.h:30: warning: "TRACE_DEFINE_SYM_FNS" redefined
   30 | #define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show)                \
      |
In file included from ./include/linux/trace_events.h:11,
                 from kernel/module/main.c:14:
./include/linux/tracepoint.h:130: note: this is the location of the previous definition
  130 | #define TRACE_DEFINE_SYM_FNS(...)
      |
./include/trace/stages/init.h:54: warning: "TRACE_DEFINE_SYM_LIST" redefined
   54 | #define TRACE_DEFINE_SYM_LIST(_symbol_id, ...)                          \
      |
./include/linux/tracepoint.h:131: note: this is the location of the previous definition
  131 | #define TRACE_DEFINE_SYM_LIST(...)
      |
Johannes Berg March 27, 2024, 9:24 p.m. UTC | #2
On Wed, 2024-03-27 at 21:11 +0000, Simon Horman wrote:
> 
> I'm seeing some allmodconfig build problems with this applied on top of
> net-next.

> ./include/trace/stages/init.h:30: warning: "TRACE_DEFINE_SYM_FNS" redefined

> ./include/trace/stages/init.h:54: warning: "TRACE_DEFINE_SYM_LIST" redefined

Yeah, the 0-day bot reported that too, sorry about that. It needs two
lines to #undef these in init.h before their definition, just like all
other macros there. Not sure why my builds didn't show that, maybe it
doesn't affect all users.

johannes
diff mbox series

Patch

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f7749d0f2562..88de434578a5 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -256,7 +256,8 @@ 
 #define FTRACE_EVENTS()							\
 	. = ALIGN(8);							\
 	BOUNDED_SECTION(_ftrace_events)					\
-	BOUNDED_SECTION_BY(_ftrace_eval_map, _ftrace_eval_maps)
+	BOUNDED_SECTION_BY(_ftrace_eval_map, _ftrace_eval_maps)		\
+	BOUNDED_SECTION(_ftrace_sym_defs)
 #else
 #define FTRACE_EVENTS()
 #endif
diff --git a/include/linux/module.h b/include/linux/module.h
index 1153b0d99a80..571e5e8f17b6 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -524,6 +524,8 @@  struct module {
 	unsigned int num_trace_events;
 	struct trace_eval_map **trace_evals;
 	unsigned int num_trace_evals;
+	struct trace_sym_def **trace_sym_defs;
+	unsigned int num_trace_sym_defs;
 #endif
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 	unsigned int num_ftrace_callsites;
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 6f9bdfb09d1d..bc7045d535d0 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -27,6 +27,13 @@  const char *trace_print_flags_seq(struct trace_seq *p, const char *delim,
 const char *trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
 				    const struct trace_print_flags *symbol_array);
 
+const char *trace_print_sym_seq(struct trace_seq *p, unsigned long long val,
+				const char *(*lookup)(unsigned long long val));
+const char *trace_sym_lookup(const struct trace_sym_entry *list,
+			     size_t len, unsigned long long value);
+void trace_sym_show(struct seq_file *m,
+		    const struct trace_sym_entry *list, size_t len);
+
 #if BITS_PER_LONG == 32
 const char *trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,
 		      unsigned long long flags,
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 689b6d71590e..cc3b387953d1 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -31,6 +31,24 @@  struct trace_eval_map {
 	unsigned long		eval_value;
 };
 
+struct trace_sym_def {
+	const char		*system;
+	const char		*symbol_id;
+	/* may return NULL, called under rcu_read_lock() */
+	const char *		(*lookup)(unsigned long long);
+	/*
+	 * Must print the list: ', { val, "name"}, ...'
+	 * with no trailing comma, but with the leading ', '
+	 * to simplify things:
+	 */
+	void 			(*show)(struct seq_file *);
+};
+
+struct trace_sym_entry {
+	unsigned long long	value;
+	const char		*name;
+};
+
 #define TRACEPOINT_DEFAULT_PRIO	10
 
 extern struct srcu_struct tracepoint_srcu;
@@ -109,6 +127,8 @@  extern void syscall_unregfunc(void);
 
 #define TRACE_DEFINE_ENUM(x)
 #define TRACE_DEFINE_SIZEOF(x)
+#define TRACE_DEFINE_SYM_FNS(...)
+#define TRACE_DEFINE_SYM_LIST(...)
 
 #ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
 static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
diff --git a/include/trace/stages/init.h b/include/trace/stages/init.h
index 000bcfc8dd2e..251ab22485d1 100644
--- a/include/trace/stages/init.h
+++ b/include/trace/stages/init.h
@@ -23,6 +23,60 @@  TRACE_MAKE_SYSTEM_STR();
 	__section("_ftrace_eval_map")			\
 	*TRACE_SYSTEM##_##a = &__##TRACE_SYSTEM##_##a
 
+/*
+ * Define a symbol for __print_sym by giving lookup and
+ * show functions. See &struct trace_sym_def.
+ */
+#define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show)		\
+	_TRACE_DEFINE_SYM_FNS(TRACE_SYSTEM, _symbol_id, _lookup, _show)
+#define _TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)	\
+	__TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)
+#define __TRACE_DEFINE_SYM_FNS(_system, _symbol_id, _lookup, _show)	\
+	___TRACE_DEFINE_SYM_FNS(_system ## _ ## _symbol_id, _symbol_id,	\
+				_lookup, _show)
+#define ___TRACE_DEFINE_SYM_FNS(_name, _symbol_id, _lookup, _show)	\
+	static struct trace_sym_def					\
+	__trace_sym_def_ ## _name = {					\
+		.system = TRACE_SYSTEM_STRING,				\
+		/* need the ) for later strcmp */			\
+		.symbol_id = #_symbol_id ")",				\
+		.lookup = _lookup,					\
+		.show = _show,						\
+	};								\
+	static struct trace_sym_def 					\
+	__section("_ftrace_sym_defs")					\
+	*__trace_sym_def_p_ ## _name = &__trace_sym_def_ ## _name
+
+/*
+ * Define a symbol for __print_sym by giving lookup and
+ * show functions. See &struct trace_sym_def.
+ */
+#define TRACE_DEFINE_SYM_LIST(_symbol_id, ...)				\
+	_TRACE_DEFINE_SYM_LIST(TRACE_SYSTEM, _symbol_id, __VA_ARGS__)
+#define _TRACE_DEFINE_SYM_LIST(_system, _symbol_id, ...)		\
+	__TRACE_DEFINE_SYM_LIST(_system, _symbol_id, __VA_ARGS__)
+#define __TRACE_DEFINE_SYM_LIST(_system, _symbol_id, ...)		\
+	___TRACE_DEFINE_SYM_LIST(_system ## _ ## _symbol_id, _symbol_id,\
+				 __VA_ARGS__)
+#define ___TRACE_DEFINE_SYM_LIST(_name, _symbol_id, ...)		\
+	static struct trace_sym_entry					\
+	__trace_sym_list_ ## _name[] = { __VA_ARGS__ };			\
+	static const char *						\
+	__trace_sym_lookup_ ## _name(unsigned long long value)		\
+	{								\
+		return trace_sym_lookup(__trace_sym_list_ ## _name,	\
+			ARRAY_SIZE(__trace_sym_list_ ## _name), value);	\
+	}								\
+	static void							\
+	__trace_sym_show_ ## _name(struct seq_file *m)			\
+	{								\
+		trace_sym_show(m, __trace_sym_list_ ## _name,		\
+			       ARRAY_SIZE(__trace_sym_list_ ## _name));	\
+	}								\
+	___TRACE_DEFINE_SYM_FNS(_name, _symbol_id,			\
+				__trace_sym_lookup_ ## _name,		\
+				__trace_sym_show_ ## _name)
+
 #undef TRACE_DEFINE_SIZEOF
 #define TRACE_DEFINE_SIZEOF(a)				\
 	static struct trace_eval_map __used __initdata	\
diff --git a/include/trace/stages/stage2_data_offsets.h b/include/trace/stages/stage2_data_offsets.h
index 8b0cff06d346..5afd9de7deb3 100644
--- a/include/trace/stages/stage2_data_offsets.h
+++ b/include/trace/stages/stage2_data_offsets.h
@@ -5,6 +5,12 @@ 
 #undef TRACE_DEFINE_ENUM
 #define TRACE_DEFINE_ENUM(a)
 
+#undef TRACE_DEFINE_SYM_FNS
+#define TRACE_DEFINE_SYM_FNS(_symbol_id, _lookup, _show)
+
+#undef TRACE_DEFINE_SYM_LIST
+#define TRACE_DEFINE_SYM_LIST(_symbol_id, ...)
+
 #undef TRACE_DEFINE_SIZEOF
 #define TRACE_DEFINE_SIZEOF(a)
 
diff --git a/include/trace/stages/stage3_trace_output.h b/include/trace/stages/stage3_trace_output.h
index c1fb1355d309..d2c6458b62dc 100644
--- a/include/trace/stages/stage3_trace_output.h
+++ b/include/trace/stages/stage3_trace_output.h
@@ -79,6 +79,15 @@ 
 		trace_print_symbols_seq(p, value, symbols);		\
 	})
 
+#undef __print_sym
+#define __print_sym(value, symbol_id)					\
+	___print_sym(TRACE_SYSTEM, value, symbol_id)
+#define ___print_sym(sys, value, symbol_id)				\
+	____print_sym(sys, value, symbol_id)
+#define ____print_sym(sys, value, symbol_id)				\
+	trace_print_sym_seq(p, value,					\
+		__trace_sym_def_p_ ## sys ## _ ## symbol_id->lookup)
+
 #undef __print_flags_u64
 #undef __print_symbolic_u64
 #if BITS_PER_LONG == 32
diff --git a/include/trace/stages/stage7_class_define.h b/include/trace/stages/stage7_class_define.h
index bcb960d16fc0..cf552916935f 100644
--- a/include/trace/stages/stage7_class_define.h
+++ b/include/trace/stages/stage7_class_define.h
@@ -25,6 +25,9 @@ 
 #undef __print_hex_dump
 #undef __get_buf
 
+#undef __print_sym
+#define __print_sym(value, symbol_id)	__print_sym(value:symbol_id)
+
 /*
  * The below is not executed in the kernel. It is only what is
  * displayed in the print format for userspace to parse.
diff --git a/kernel/module/main.c b/kernel/module/main.c
index e1e8a7a9d6c1..babc45cbf1de 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2161,6 +2161,9 @@  static int find_module_sections(struct module *mod, struct load_info *info)
 	mod->trace_evals = section_objs(info, "_ftrace_eval_map",
 					sizeof(*mod->trace_evals),
 					&mod->num_trace_evals);
+	mod->trace_sym_defs = section_objs(info, "_ftrace_sym_defs",
+					   sizeof(*mod->trace_sym_defs),
+					   &mod->num_trace_sym_defs);
 #endif
 #ifdef CONFIG_TRACING
 	mod->trace_bprintk_fmt_start = section_objs(info, "__trace_printk_fmt",
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 7c364b87352e..24f185836dcc 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1570,6 +1570,93 @@  static void *f_next(struct seq_file *m, void *v, loff_t *pos)
 		return node;
 }
 
+extern struct trace_sym_def *__start_ftrace_sym_defs[];
+extern struct trace_sym_def *__stop_ftrace_sym_defs[];
+
+static void show_sym_list(struct seq_file *m, struct trace_event_call *call,
+			  const char *name)
+{
+	struct trace_sym_def **sym_defs;
+	unsigned int n_sym_defs, i;
+
+	if (call->module) {
+		struct module *mod = call->module;
+
+		sym_defs = mod->trace_sym_defs;
+		n_sym_defs = mod->num_trace_sym_defs;
+	} else {
+		sym_defs = __start_ftrace_sym_defs;
+		n_sym_defs = __stop_ftrace_sym_defs - __start_ftrace_sym_defs;
+	}
+
+	for (i = 0; i < n_sym_defs; i++) {
+		if (!sym_defs[i])
+			continue;
+		if (sym_defs[i]->system != call->class->system)
+			continue;
+		if (strncmp(name, sym_defs[i]->symbol_id,
+			    strlen(sym_defs[i]->symbol_id)))
+			continue;
+		if (sym_defs[i]->show)
+			sym_defs[i]->show(m);
+		break;
+	}
+}
+
+static void show_print_fmt(struct seq_file *m, struct trace_event_call *call)
+{
+	char *ptr = call->print_fmt;
+	bool in_print_sym = false;
+	int quote = 0;
+
+	seq_puts(m, "\nprint fmt: ");
+	while (*ptr) {
+		if (*ptr == '\\') {
+			seq_putc(m, *ptr);
+			ptr++;
+			/* paranoid */
+			if (!*ptr)
+				break;
+			goto next;
+		}
+		if (*ptr == '"') {
+			quote ^= 1;
+			goto next;
+		}
+		if (quote)
+			goto next;
+
+		if (in_print_sym && *ptr != ':')
+			goto next;
+
+		if (in_print_sym && *ptr == ':') {
+			const char *name;
+
+			ptr++;
+			name = ptr;
+			/* skip the name */
+			while (*ptr && *ptr != ')')
+				ptr++;
+			/* and show the actual list inline now */
+			show_sym_list(m, call, name);
+			in_print_sym = false;
+			continue;
+		}
+
+		if (strncmp(ptr, "__print_sym(", 12) == 0) {
+			ptr += 12;
+			seq_puts(m, "__print_symbolic(");
+			in_print_sym = true;
+			continue;
+		}
+next:
+		seq_putc(m, *ptr);
+		ptr++;
+	}
+
+	seq_putc(m, '\n');
+}
+
 static int f_show(struct seq_file *m, void *v)
 {
 	struct trace_event_call *call = event_file_data(m->private);
@@ -1588,8 +1675,7 @@  static int f_show(struct seq_file *m, void *v)
 		return 0;
 
 	case FORMAT_PRINTFMT:
-		seq_printf(m, "\nprint fmt: %s\n",
-			   call->print_fmt);
+		show_print_fmt(m, call);
 		return 0;
 	}
 
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index d8b302d01083..8a3aa661ea46 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -124,6 +124,51 @@  trace_print_symbols_seq(struct trace_seq *p, unsigned long val,
 }
 EXPORT_SYMBOL(trace_print_symbols_seq);
 
+const char *trace_sym_lookup(const struct trace_sym_entry *list,
+			     size_t len, unsigned long long value)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (list[i].value == value)
+			return list[i].name;
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(trace_sym_lookup);
+
+void trace_sym_show(struct seq_file *m,
+		    const struct trace_sym_entry *list, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++)
+		seq_printf(m, ", { %lld, \"%s\" }",
+			   list[i].value, list[i].name);
+}
+EXPORT_SYMBOL(trace_sym_show);
+
+const char *
+trace_print_sym_seq(struct trace_seq *p, unsigned long long val,
+		    const char *(*lookup)(unsigned long long val))
+{
+	const char *ret = trace_seq_buffer_ptr(p);
+	const char *name;
+
+	rcu_read_lock();
+	name = lookup(val);
+	if (name)
+		trace_seq_puts(p, name);
+	else
+		trace_seq_printf(p, "0x%llx", val);
+	rcu_read_unlock();
+
+	trace_seq_putc(p, 0);
+
+	return ret;
+}
+EXPORT_SYMBOL(trace_print_sym_seq);
+
 #if BITS_PER_LONG == 32
 const char *
 trace_print_flags_seq_u64(struct trace_seq *p, const char *delim,