linux-kernel - Re: [PATCH] riscv/ptrace: add new regset to get original a0 register

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Message-ID: <31d48f53-eaf0-445e-b9e3-7c56070ff6ad@coelacanthus.name>
Date: Tue, 3 Dec 2024 17:33:17 +0800
From: Celeste Liu <uwu@...lacanthus.name>
To: Björn Töpel <bjorn@...nel.org>,
 Oleg Nesterov <oleg@...hat.com>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Eric Biederman <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>
Cc: Alexandre Ghiti <alex@...ti.fr>, "Dmitry V. Levin" <ldv@...ace.io>,
 Andrea Bolognani <abologna@...hat.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ron Economos <re@...z.net>,
 Felix Yan <felixonmars@...hlinux.org>, Ruizhe Pan <c141028@...il.com>,
 Shiqi Zhang <shiqi@...c.iscas.ac.cn>, Guo Ren <guoren@...nel.org>,
 Yao Zi <ziyao@...root.org>, Han Gao <gaohan@...as.ac.cn>,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, stable@...r.kernel.org
Subject: Re: [PATCH] riscv/ptrace: add new regset to get original a0 register

On 2024-12-02 23:44, Björn Töpel wrote:

> Thanks for working on this!
> 
> Celeste Liu <uwu@...lacanthus.name> writes:
> 
>> The orig_a0 is missing in struct user_regs_struct of riscv, and there is
>> no way to add it without breaking UAPI. (See Link tag below)
>>
>> Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
>> access original a0 register from userspace via ptrace API.
>>
>> Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
>> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
>> ---
>>  arch/riscv/kernel/ptrace.c | 33 +++++++++++++++++++++++++++++++++
>>  include/uapi/linux/elf.h   |  1 +
>>  2 files changed, 34 insertions(+)
>>
>> diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
>> index ea67e9fb7a583683b922fe2c017ea61f3bc848db..faa46de9000376eb445a32d43a40210d7b846844 100644
>> --- a/arch/riscv/kernel/ptrace.c
>> +++ b/arch/riscv/kernel/ptrace.c
>> @@ -31,6 +31,7 @@ enum riscv_regset {
>>  #ifdef CONFIG_RISCV_ISA_SUPM
>>  	REGSET_TAGGED_ADDR_CTRL,
>>  #endif
>> +	REGSET_ORIG_A0,
>>  };
>>  
>>  static int riscv_gpr_get(struct task_struct *target,
>> @@ -184,6 +185,30 @@ static int tagged_addr_ctrl_set(struct task_struct *target,
>>  }
>>  #endif
>>  
>> +static int riscv_orig_a0_get(struct task_struct *target,
>> +			     const struct user_regset *regset,
>> +			     struct membuf to)
> 
> Use full 100 chars!

Linux code style prefer 80 limit.

> 
>> +{
>> +	return membuf_store(&to, task_pt_regs(target)->orig_a0);
>> +}
>> +
>> +static int riscv_orig_a0_set(struct task_struct *target,
>> +			     const struct user_regset *regset,
>> +			     unsigned int pos, unsigned int count,
>> +			     const void *kbuf, const void __user *ubuf)
> 
> Dito!
> 
>> +{
>> +	int orig_a0 = task_pt_regs(target)->orig_a0;
> 
> 64b regs on RV64.

Oh, my bad.

> 
>> +	int ret;
>> +
>> +	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &orig_a0, 0, -1);
>> +	if (ret)
>> +		return ret;
>> +
>> +	task_pt_regs(target)->orig_a0 = orig_a0;
>> +	return ret;
>> +}
>> +
>> +
> 
> Multiple blanks.
> 
>>  static const struct user_regset riscv_user_regset[] = {
>>  	[REGSET_X] = {
>>  		.core_note_type = NT_PRSTATUS,
>> @@ -224,6 +249,14 @@ static const struct user_regset riscv_user_regset[] = {
>>  		.set = tagged_addr_ctrl_set,
>>  	},
>>  #endif
>> +	[REGSET_ORIG_A0] = {
>> +		.core_note_type = NT_RISCV_ORIG_A0,
>> +		.n = 1,
>> +		.size = sizeof(elf_greg_t),
>> +		.align = sizeof(elf_greg_t),
> 
> ...and sizeof(elf_greg_t) is 64b in RV64 -- mismatch above.

v2 has been sent.

> 
> 
> Björn