linux-kernel - [PATCH bpf-next] bpf: remove is_return in struct bpf_session_run

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Message-ID: <20250922095705.252519-1-dongml2@chinatelecom.cn>
Date: Mon, 22 Sep 2025 17:57:05 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: jolsa@...nel.org
Cc: kpsingh@...nel.org,
	mattbobrowski@...gle.com,
	song@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	sdf@...ichev.me,
	haoluo@...gle.com,
	rostedt@...dmis.org,
	mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH bpf-next] bpf: remove is_return in struct bpf_session_run_ctx

The "data" in struct bpf_session_run_ctx is always 8-bytes aligned.
Therefore, we can store the "is_return" to the last bit of the "data",
which can make bpf_session_run_ctx 8-bytes aligned and save memory.

Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
---
 kernel/trace/bpf_trace.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f2360579658e..b6a34aa039f6 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2269,7 +2269,6 @@ fs_initcall(bpf_event_init);
 
 struct bpf_session_run_ctx {
 	struct bpf_run_ctx run_ctx;
-	bool is_return;
 	void *data;
 };
 
@@ -2535,8 +2534,7 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
 {
 	struct bpf_kprobe_multi_run_ctx run_ctx = {
 		.session_ctx = {
-			.is_return = is_return,
-			.data = data,
+			.data = (void *)((unsigned long)data | !!is_return),
 		},
 		.link = link,
 		.entry_ip = entry_ip,
@@ -3058,8 +3056,7 @@ static int uprobe_prog_run(struct bpf_uprobe *uprobe,
 	struct bpf_uprobe_multi_link *link = uprobe->link;
 	struct bpf_uprobe_multi_run_ctx run_ctx = {
 		.session_ctx = {
-			.is_return = is_return,
-			.data = data,
+			.data = (void *)((unsigned long)data | !!is_return),
 		},
 		.entry_ip = entry_ip,
 		.uprobe = uprobe,
@@ -3316,7 +3313,7 @@ __bpf_kfunc bool bpf_session_is_return(void)
 	struct bpf_session_run_ctx *session_ctx;
 
 	session_ctx = container_of(current->bpf_ctx, struct bpf_session_run_ctx, run_ctx);
-	return session_ctx->is_return;
+	return (unsigned long)session_ctx->data & 1;
 }
 
 __bpf_kfunc __u64 *bpf_session_cookie(void)
@@ -3324,7 +3321,7 @@ __bpf_kfunc __u64 *bpf_session_cookie(void)
 	struct bpf_session_run_ctx *session_ctx;
 
 	session_ctx = container_of(current->bpf_ctx, struct bpf_session_run_ctx, run_ctx);
-	return session_ctx->data;
+	return (__u64 *)((unsigned long)session_ctx->data & ~1);
 }
 
 __bpf_kfunc_end_defs();
-- 
2.51.0