linux-kernel - Re: [PATCH v7] function_graph: Enable funcgraph-args and funcgraph-retaddr to work simultaneously

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Message-ID: <20251124201258.0e34ac3b@gandalf.local.home>
Date: Mon, 24 Nov 2025 20:12:58 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Donglin Peng <dolinux.peng@...il.com>
Cc: linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
 Donglin Peng <pengdonglin@...omi.com>, Sven Schnelle <svens@...ux.ibm.com>,
 Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH v7] function_graph: Enable funcgraph-args and
 funcgraph-retaddr to work simultaneously

On Mon, 24 Nov 2025 16:54:40 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 24 Nov 2025 16:47:01 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > > --- a/kernel/trace/trace_entries.h
> > > +++ b/kernel/trace/trace_entries.h
> > > @@ -95,14 +95,14 @@ FTRACE_ENTRY_PACKED(fgraph_retaddr_entry, fgraph_retaddr_ent_entry,
> > >  	TRACE_GRAPH_RETADDR_ENT,
> > >  
> > >  	F_STRUCT(
> > > -		__field_struct(	struct fgraph_retaddr_ent,	graph_ent	)
> > > +		__field_struct(	struct ftrace_graph_ent,	graph_ent	)
> > >  		__field_packed(	unsigned long,	graph_ent,	func		)
> > >  		__field_packed(	unsigned int,	graph_ent,	depth		)
> > > -		__field_packed(	unsigned long,	graph_ent,	retaddr		)    
> > 
> > You can't delete the retaddr without breaking user space.
> > 
> > Please keep that here.  
> 
> I added this, and user space works again:
> 
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index 593a74663c65..4666b6179056 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -98,6 +98,7 @@ FTRACE_ENTRY_PACKED(fgraph_retaddr_entry, fgraph_retaddr_ent_entry,
>  		__field_struct(	struct ftrace_graph_ent,	graph_ent	)
>  		__field_packed(	unsigned long,	graph_ent,	func		)
>  		__field_packed(	unsigned int,	graph_ent,	depth		)
> +		__field_packed(	unsigned long,	graph_ent,	retaddr		)
>  		__dynamic_array(unsigned long,	args				)
>  	),
>  

Nope, this wasn't enough. I got garbage from this. The following patch
appears to make it all work though (this is against your patch that was
forward ported to my for-next branch):

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 88cb54d73bdb..ba180d19423e 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1121,12 +1121,10 @@ static inline void ftrace_init(void) { }
 
 /*
  * Structure that defines an entry function trace.
- * It's already packed but the attribute "packed" is needed
- * to remove extra padding at the end.
  */
 struct ftrace_graph_ent {
 	unsigned long func; /* Current function */
-	int depth;
+	unsigned long depth;
 } __packed;
 
 /*
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 05fb6c9279e3..d509a5041d38 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -60,6 +60,13 @@ enum trace_type {
 	__TRACE_LAST_TYPE,
 };
 
+/*
+ * Structure that defines an entry function trace with retaddr.
+ */
+struct fgraph_retaddr_ent {
+	struct ftrace_graph_ent		ent;
+	unsigned long retaddr;  /* Return address */
+} __packed;
 
 #undef __field
 #define __field(type, item)		type	item;
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index 593a74663c65..87f4228374cd 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -80,11 +80,11 @@ FTRACE_ENTRY(funcgraph_entry, ftrace_graph_ent_entry,
 	F_STRUCT(
 		__field_struct(	struct ftrace_graph_ent,	graph_ent	)
 		__field_packed(	unsigned long,	graph_ent,	func		)
-		__field_packed(	unsigned int,	graph_ent,	depth		)
+		__field_packed(	unsigned long,	graph_ent,	depth		)
 		__dynamic_array(unsigned long,	args				)
 	),
 
-	F_printk("--> %ps (%u)", (void *)__entry->func, __entry->depth)
+	F_printk("--> %ps (%lu)", (void *)__entry->func, __entry->depth)
 );
 
 #ifdef CONFIG_FUNCTION_GRAPH_RETADDR
@@ -95,13 +95,14 @@ FTRACE_ENTRY_PACKED(fgraph_retaddr_entry, fgraph_retaddr_ent_entry,
 	TRACE_GRAPH_RETADDR_ENT,
 
 	F_STRUCT(
-		__field_struct(	struct ftrace_graph_ent,	graph_ent	)
-		__field_packed(	unsigned long,	graph_ent,	func		)
-		__field_packed(	unsigned int,	graph_ent,	depth		)
+		__field_struct(	struct fgraph_retaddr_ent,	graph_ent	)
+		__field_packed(	unsigned long,	graph_ent.ent,	func		)
+		__field_packed(	unsigned long,	graph_ent.ent,	depth		)
+		__field_packed(	unsigned long,	graph_ent,	retaddr		)
 		__dynamic_array(unsigned long,	args				)
 	),
 
-	F_printk("--> %ps (%u) <- %ps", (void *)__entry->func, __entry->depth,
+	F_printk("--> %ps (%lu) <- %ps", (void *)__entry->func, __entry->depth,
 		(void *)__entry->args[0])
 );
 
-- Steve