[PATCH] riscv, libbpf: use a0 for RC register

From: Yixun Lan <dlan@gentoo.org>
To: linux-riscv@lists.infradead.org, "Björn Töpel" <bjorn@kernel.org>,
	bpf@vger.kernel.org
Cc: Palmer Dabbelt <palmer@dabbelt.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Hengqi Chen <chenhengqi@outlook.com>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Yixun Lan <dlan@gentoo.org>
Subject: [PATCH] riscv, libbpf: use a0 for RC register
Date: Wed,  6 Jul 2022 22:02:04 +0800	[thread overview]
Message-ID: <20220706140204.47926-1-dlan@gentoo.org> (raw)

According to the RISC-V calling convention register usage here[1],
a0 is used as return value register, so rename it to make it consistent
with the spec.

[1] section 18.2, table 18.2
https://riscv.org/wp-content/uploads/2015/01/riscv-calling.pdf

Fixes: 589fed479ba1 ("riscv, libbpf: Add RISC-V (RV64) support to bpf_tracing.h")
Signed-off-by: Yixun Lan <dlan@gentoo.org>

---

I'm adding a Fixes tag here, although the original version may just work fine,
and shouldn't be considered as a real error. But, the benefit is that we could
make it consistent with RISC-V spec, and all other tools will follow the same usage.

thanks, and let's me if there is any issue that I may not noticed..
---
 tools/lib/bpf/bpf_tracing.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
index 01ce121c302df..11f9096407fc4 100644
--- a/tools/lib/bpf/bpf_tracing.h
+++ b/tools/lib/bpf/bpf_tracing.h
@@ -233,7 +233,7 @@ struct pt_regs___arm64 {
 #define __PT_PARM5_REG a4
 #define __PT_RET_REG ra
 #define __PT_FP_REG s0
-#define __PT_RC_REG a5
+#define __PT_RC_REG a0
 #define __PT_SP_REG sp
 #define __PT_IP_REG pc
 /* riscv does not select ARCH_HAS_SYSCALL_WRAPPER. */
-- 
2.35.1

