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Message-ID: <26a42f0c-db3b-9330-de5c-68bf44976201@loongson.cn>
Date: Wed, 26 Oct 2022 21:24:10 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: WANG Xuerui <kernel@...0n.name>,
Huacai Chen <chenhuacai@...nel.org>,
Oleg Nesterov <oleg@...hat.com>
Cc: Xi Ruoyao <xry111@...111.site>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 RESEND] LoongArch: Remove unused kernel stack padding
Hi, Xuerui,
在 2022/10/26 15:27, WANG Xuerui 写道:
> On 2022/10/26 11:55, Jinyang He wrote:
>> Kernel stack padding looks like obey MIPS o32 Calling Convention, as
>> LoongArch is inspired by MIPS and keep it. Remove it avoid not clear
>> code.
>
> Just some improvement to the commit message so it's clearer:
>
> "The current LoongArch kernel stack is padded as if obeying the MIPS
> o32 calling convention, signifying the port's MIPS lineage but no
> longer making sense. Remove the padding for clarity."
Thanks, I'll improve it and send it later.
>
>>
>> Link:
>> https://lore.kernel.org/loongarch/1662130897-13156-1-git-send-email-hejinyang@loongson.cn/
>>
>
> I think this blank line between the "Link" and S-o-b tags could be
> removed.
Ok.
>
>> Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
>> ---
>> v2: Remove TOP_OF_KERNEL_STACK_PADDING
>> Remove 'init stack pointer' in head.S
>>
>> arch/loongarch/include/asm/processor.h | 2 +-
>> arch/loongarch/include/asm/ptrace.h | 2 +-
>> arch/loongarch/kernel/head.S | 3 +--
>> arch/loongarch/kernel/process.c | 4 ++--
>> arch/loongarch/kernel/switch.S | 2 +-
>> 5 files changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/processor.h
>> b/arch/loongarch/include/asm/processor.h
>> index 6954dc5d24e9..7184f1dc61f2 100644
>> --- a/arch/loongarch/include/asm/processor.h
>> +++ b/arch/loongarch/include/asm/processor.h
>> @@ -191,7 +191,7 @@ static inline void flush_thread(void)
>> unsigned long __get_wchan(struct task_struct *p);
>> #define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
>> - THREAD_SIZE - 32 - sizeof(struct pt_regs))
>> + THREAD_SIZE - sizeof(struct pt_regs))
>> #define task_pt_regs(tsk) ((struct pt_regs *)__KSTK_TOS(tsk))
>> #define KSTK_EIP(tsk) (task_pt_regs(tsk)->csr_era)
>> #define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[3])
>> diff --git a/arch/loongarch/include/asm/ptrace.h
>> b/arch/loongarch/include/asm/ptrace.h
>> index 7437b9366c3b..59c4608de91d 100644
>> --- a/arch/loongarch/include/asm/ptrace.h
>> +++ b/arch/loongarch/include/asm/ptrace.h
>> @@ -133,7 +133,7 @@ static inline void die_if_kernel(const char *str,
>> struct pt_regs *regs)
>> #define current_pt_regs() \
>> ({ \
>> unsigned long sp = (unsigned long)__builtin_frame_address(0); \
>> - (struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1 - 32) - 1; \
>> + (struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1) - 1; \
>> })
>> /* Helpers for working with the user stack pointer */
>> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
>> index 97425779ce9f..84970e266658 100644
>> --- a/arch/loongarch/kernel/head.S
>> +++ b/arch/loongarch/kernel/head.S
>> @@ -84,10 +84,9 @@ SYM_CODE_START(kernel_entry) # kernel
>> entry point
>> la.pcrel tp, init_thread_union
>> /* Set the SP after an empty pt_regs. */
>> - PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE)
>> + PTR_LI sp, (_THREAD_SIZE - PT_SIZE)
>> PTR_ADD sp, sp, tp
>> set_saved_sp sp, t0, t1
>> - PTR_ADDI sp, sp, -4 * SZREG # init stack pointer
>> bl start_kernel
>> ASM_BUG()
>> diff --git a/arch/loongarch/kernel/process.c
>> b/arch/loongarch/kernel/process.c
>> index 1256e3582475..2526b68f1c0f 100644
>> --- a/arch/loongarch/kernel/process.c
>> +++ b/arch/loongarch/kernel/process.c
>> @@ -129,7 +129,7 @@ int copy_thread(struct task_struct *p, const
>> struct kernel_clone_args *args)
>> unsigned long clone_flags = args->flags;
>> struct pt_regs *childregs, *regs = current_pt_regs();
>> - childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
>> + childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
>> /* set up new TSS. */
>> childregs = (struct pt_regs *) childksp - 1;
>> @@ -236,7 +236,7 @@ bool in_task_stack(unsigned long stack, struct
>> task_struct *task,
>> struct stack_info *info)
>> {
>> unsigned long begin = (unsigned long)task_stack_page(task);
>> - unsigned long end = begin + THREAD_SIZE - 32;
>> + unsigned long end = begin + THREAD_SIZE;
>> if (stack < begin || stack >= end)
>> return false;
>> diff --git a/arch/loongarch/kernel/switch.S
>> b/arch/loongarch/kernel/switch.S
>> index 43ebbc3990f7..202a163cb32f 100644
>> --- a/arch/loongarch/kernel/switch.S
>> +++ b/arch/loongarch/kernel/switch.S
>> @@ -26,7 +26,7 @@ SYM_FUNC_START(__switch_to)
>> move tp, a2
>> cpu_restore_nonscratch a1
>> - li.w t0, _THREAD_SIZE - 32
>> + li.w t0, _THREAD_SIZE
>> PTR_ADD t0, t0, tp
>> set_saved_sp t0, t1, t2
>
> Otherwise LGTM, assuming you have tested it before sending (I don't
> currently have the capacity to immediately test this for you)...
>
> Reviewed-by: WANG Xuerui <git@...0n.name>
Emm, to be honest, I didn't do tests like LTP. I ususally do development
on CLFS-LoongArch while kernel has this patch. And it works normally.
Thanks,
Jinyang
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