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Message-ID: <20250819182130.75542133@gandalf.local.home>
Date: Tue, 19 Aug 2025 18:21:30 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
bpf@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland
<mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Andrew Morton <akpm@...ux-foundation.org>, Sven Schnelle
<svens@...ux.ibm.com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer
Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Guo Ren
<guoren@...nel.org>, Donglin Peng <dolinux.peng@...il.com>, Zheng Yejian
<zhengyejian@...weicloud.com>
Subject: Re: [PATCH v4 2/4] ftrace: Add support for function argument to
graph tracer
On Thu, 14 Aug 2025 13:05:35 -0400
Sasha Levin <sashal@...nel.org> wrote:
> On Wed,
> Got a small build error:
>
> kernel/trace/trace_functions_graph.c: In function ‘get_return_for_leaf’:
> ./include/linux/stddef.h:16:33: error: ‘struct fgraph_retaddr_ent_entry’ has no member named ‘args’
> 16 | #define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
> | ^~~~~~~~~~~~~~~~~~
> kernel/trace/trace_functions_graph.c:640:40: note: in expansion of macro ‘offsetof’
> 640 | size = offsetof(struct fgraph_retaddr_ent_entry, args);
> | ^~~~~~~~
>
> Does this look right on top of your patch:
Bah, it was on the todo list to add args to retaddr. But it never was done.
>
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 25ea71edb8da..f0f37356ef29 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -637,20 +637,21 @@ get_return_for_leaf(struct trace_iterator *iter,
> */
> if (unlikely(curr->ent.type == TRACE_GRAPH_RETADDR_ENT)) {
> data->ent.rent = *(struct fgraph_retaddr_ent_entry *)curr;
> - size = offsetof(struct fgraph_retaddr_ent_entry, args);
> + /* fgraph_retaddr_ent_entry doesn't have args field */
"doesn't have args field" yet!
> + size = sizeof(struct fgraph_retaddr_ent_entry);
> + args_size = 0;
> } else {
> data->ent.ent = *curr;
> size = offsetof(struct ftrace_graph_ent_entry, args);
> + /* If this has args, then append them to after the ent. */
> + args_size = iter->ent_size - size;
> + if (args_size > sizeof(long) * FTRACE_REGS_MAX_ARGS)
> + args_size = sizeof(long) * FTRACE_REGS_MAX_ARGS;
> +
> + if (args_size >= sizeof(long))
> + memcpy((void *)&data->ent.ent + size,
> + (void*)curr + size, args_size);
> }
Here's a different update:
-- Steve
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 66e1a527cf1a..a7f4b9a47a71 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -27,14 +27,21 @@ struct fgraph_cpu_data {
unsigned long enter_funcs[FTRACE_RETFUNC_DEPTH];
};
+struct fgraph_ent_args {
+ struct ftrace_graph_ent_entry ent;
+ /* Force the sizeof of args[] to have FTRACE_REGS_MAX_ARGS entries */
+ unsigned long args[FTRACE_REGS_MAX_ARGS];
+};
+
struct fgraph_data {
struct fgraph_cpu_data __percpu *cpu_data;
/* Place to preserve last processed entry. */
union {
- struct ftrace_graph_ent_entry ent;
+ struct fgraph_ent_args ent;
+ /* TODO allow retaddr to have args */
struct fgraph_retaddr_ent_entry rent;
- } ent;
+ };
struct ftrace_graph_ret_entry ret;
int failed;
int cpu;
@@ -627,10 +634,13 @@ get_return_for_leaf(struct trace_iterator *iter,
* Save current and next entries for later reference
* if the output fails.
*/
- if (unlikely(curr->ent.type == TRACE_GRAPH_RETADDR_ENT))
- data->ent.rent = *(struct fgraph_retaddr_ent_entry *)curr;
- else
- data->ent.ent = *curr;
+ if (unlikely(curr->ent.type == TRACE_GRAPH_RETADDR_ENT)) {
+ data->rent = *(struct fgraph_retaddr_ent_entry *)curr;
+ } else {
+ int size = min((int)sizeof(data->ent), (int)iter->ent_size);
+
+ memcpy(&data->ent, curr, size);
+ }
/*
* If the next event is not a return type, then
* we only care about what type it is. Otherwise we can
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