Re: [PATCH v4 2/4] ftrace: Add support for function argument to graph tracer
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2025-08-19 22:21:34
Also in:
bpf, lkml
Subsystem:
the rest, tracing · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
On Thu, 14 Aug 2025 13:05:35 -0400 Sasha Levin [off-list ref] 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.
quoted hunk ↗ jump to hunk
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!
quoted hunk ↗ jump to hunk
+ 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