netdev - [PATCH bpf-next v2 2/4] libbpf: Access first syscall argument with CO-RE direct read on arm64

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Message-Id: <20240831023646.1558629-3-pulehui@huaweicloud.com>
Date: Sat, 31 Aug 2024 02:36:44 +0000
From: Pu Lehui <pulehui@...weicloud.com>
To: bpf@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	netdev@...r.kernel.org,
	Andrii Nakryiko <andrii@...nel.org>
Cc: Björn Töpel <bjorn@...nel.org>,
	Ilya Leoshkevich <iii@...ux.ibm.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Pu Lehui <pulehui@...wei.com>
Subject: [PATCH bpf-next v2 2/4] libbpf: Access first syscall argument with CO-RE direct read on arm64

From: Pu Lehui <pulehui@...wei.com>

Currently PT_REGS_PARM1 SYSCALL(x) is consistent with PT_REGS_PARM1_CORE
SYSCALL(x), which will introduce the overhead of BPF_CORE_READ(), taking
into account the read pt_regs comes directly from the context, let's use
CO-RE direct read to access the first system call argument.

Suggested-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Pu Lehui <pulehui@...wei.com>
---
 tools/lib/bpf/bpf_tracing.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
index e7d9382efeb3..051c408e6aed 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -222,7 +222,7 @@ struct pt_regs___s390 {
 
 struct pt_regs___arm64 {
 	unsigned long orig_x0;
-};
+} __attribute__((preserve_access_index));
 
 /* arm64 provides struct user_pt_regs instead of struct pt_regs to userspace */
 #define __PT_REGS_CAST(x) ((const struct user_pt_regs *)(x))
@@ -241,7 +241,7 @@ struct pt_regs___arm64 {
 #define __PT_PARM4_SYSCALL_REG __PT_PARM4_REG
 #define __PT_PARM5_SYSCALL_REG __PT_PARM5_REG
 #define __PT_PARM6_SYSCALL_REG __PT_PARM6_REG
-#define PT_REGS_PARM1_SYSCALL(x) PT_REGS_PARM1_CORE_SYSCALL(x)
+#define PT_REGS_PARM1_SYSCALL(x) (((const struct pt_regs___arm64 *)(x))->orig_x0)
 #define PT_REGS_PARM1_CORE_SYSCALL(x) \
 	BPF_CORE_READ((const struct pt_regs___arm64 *)(x), __PT_PARM1_SYSCALL_REG)
 
-- 
2.34.1