[PATCH v1 1/2] riscv: Expose orig_a0 in the user_regs_struct structure

[zhouquan at iscas.ac.cn]

From: Quan Zhou <zhouquan at iscas.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.

The addition of orig_a0 also requires the following adjustments:
1) Adjust the position of orig_a0 in pt_regs to ensure correct copying.
2) MAX_REG_OFFSET should match the new bottom of pt_regs.

Suggested-by: Charlie Jenkins <charlie at rivosinc.com>
Signed-off-by: Quan Zhou <zhouquan at iscas.ac.cn>
---
 arch/riscv/include/asm/ptrace.h      | 7 ++++---
 arch/riscv/include/uapi/asm/ptrace.h | 2 ++
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index b5b0adcc85c1..380cf54c1f3d 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -12,6 +12,7 @@
 
 #ifndef __ASSEMBLY__
 
+/* MAX_REG_OFFSET should match the bottom of pt_regs */
 struct pt_regs {
 	unsigned long epc;
 	unsigned long ra;
@@ -45,12 +46,12 @@ 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
@@ -64,7 +65,7 @@ struct pt_regs {
 
 #define user_mode(regs) (((regs)->status & SR_PP) == 0)
 
-#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
+#define MAX_REG_OFFSET offsetof(struct pt_regs, cause)
 
 /* Helpers for working with the instruction pointer */
 static inline unsigned long instruction_pointer(struct pt_regs *regs)
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