linux-kernel - [RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs

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Date: Wed, 19 Jun 2024 10:01:27 +0800
From: zhouquan@...as.ac.cn
To: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Cc: oleg@...hat.com,
	paul.walmsley@...ive.com,
	palmer@...belt.com,
	aou@...s.berkeley.edu,
	andy.chiu@...ive.com,
	shuah@...nel.org,
	charlie@...osinc.com,
	zhouquan@...as.ac.cn
Subject: [RFC PATCH 1/2] riscv: Expose orig_a0 in the user_regs_struct structure

From: Quan Zhou <zhouquan@...as.ac.cn>

Expose orig_a0 to userspace to ensure that users can modify
the actual value of `a0` in the traced process through the
ptrace(PTRACE_SETREGSET, ...) path. Since user_regs_struct is
a subset of pt_regs, we also need to adjust the position of
the orig_a0 field in pt_regs to achieve the correct copy.

Signed-off-by: Quan Zhou <zhouquan@...as.ac.cn>
---
 arch/riscv/include/asm/ptrace.h      | 4 ++--
 arch/riscv/include/uapi/asm/ptrace.h | 2 ++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index b5b0adcc85c1..37f48d40ae46 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -45,12 +45,12 @@ struct pt_regs {
 	unsigned long t4;
 	unsigned long t5;
 	unsigned long t6;
+	/* a0 value before the syscall */
+	unsigned long orig_a0;
 	/* Supervisor/Machine CSRs */
 	unsigned long status;
 	unsigned long badaddr;
 	unsigned long cause;
-	/* a0 value before the syscall */
-	unsigned long orig_a0;
 };
 
 #define PTRACE_SYSEMU			0x1f
diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
index a38268b19c3d..3e37f80cb3e8 100644
--- a/arch/riscv/include/uapi/asm/ptrace.h
+++ b/arch/riscv/include/uapi/asm/ptrace.h
@@ -54,6 +54,8 @@ struct user_regs_struct {
 	unsigned long t4;
 	unsigned long t5;
 	unsigned long t6;
+	/* a0 value before the syscall */
+	unsigned long orig_a0;
 };
 
 struct __riscv_f_ext_state {
-- 
2.34.1