linux-kernel - [PATCH 1/2] riscv: ptrace: Use the correct API for `fcsr' access

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Date:   Fri, 24 Jul 2020 00:22:15 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@....com>
To:     linux-riscv@...ts.infradead.org
cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH 1/2] riscv: ptrace: Use the correct API for `fcsr' access

Adjust the calls to `user_regset_copyout' and `user_regset_copyin' in 
`riscv_fpr_get' and `riscv_fpr_set' respectively so as to use @start_pos 
and @end_pos according to API documentation in <linux/regset.h>, that is 
to point at the beginning and the end respectively of the data chunk to 
be copied.  Update @data accordingly, also for the first call, to make 
it clear which structure member is accessed.

We currently have @start_pos fixed at 0 across all calls, which works as 
a result of the implementation, in particular because we have no padding 
between the FP general registers and the FP control and status register, 
but appears not to have been the intent of the API and is not what other 
ports do, requiring one to study the copy handlers to understand what is 
going on here.

Signed-off-by: Maciej W. Rozycki <macro@....com>
Fixes: b8c8a9590e4f ("RISC-V: Add FP register ptrace support for gdb.")
Cc: stable@...r.kernel.org # 4.20+
---
 arch/riscv/kernel/ptrace.c |   14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

linux-riscv-ptrace-fcsr.diff
Index: linux-hv/arch/riscv/kernel/ptrace.c
===================================================================
--- linux-hv.orig/arch/riscv/kernel/ptrace.c
+++ linux-hv/arch/riscv/kernel/ptrace.c
@@ -61,10 +61,13 @@ static int riscv_fpr_get(struct task_str
 	int ret;
 	struct __riscv_d_ext_state *fstate = &target->thread.fstate;
 
-	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, fstate, 0,
+	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &fstate->f, 0,
 				  offsetof(struct __riscv_d_ext_state, fcsr));
 	if (!ret) {
-		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, fstate, 0,
+		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+					  &fstate->fcsr,
+					  offsetof(struct __riscv_d_ext_state,
+						   fcsr),
 					  offsetof(struct __riscv_d_ext_state, fcsr) +
 					  sizeof(fstate->fcsr));
 	}
@@ -80,10 +83,13 @@ static int riscv_fpr_set(struct task_str
 	int ret;
 	struct __riscv_d_ext_state *fstate = &target->thread.fstate;
 
-	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, fstate, 0,
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &fstate->f, 0,
 				 offsetof(struct __riscv_d_ext_state, fcsr));
 	if (!ret) {
-		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, fstate, 0,
+		ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
+					 &fstate->fcsr,
+					 offsetof(struct __riscv_d_ext_state,
+						  fcsr),
 					 offsetof(struct __riscv_d_ext_state, fcsr) +
 					 sizeof(fstate->fcsr));
 	}