Re: [PATCH v1] m68k: save extra registers on sys_exit and sys_exit_group syscall entry

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Geert,

do we need to add

.globl __sys_exit, __sys_exit_group

(and perhaps __sys_clone3) at the start of entry.S? We have that for 
__sys_fork, __sys_clone and __sys_vfork.

Cheers,

	Michael


Am 13.06.2021 um 11:38 schrieb Michael Schmitz:
> do_exit() calls prace_stop() which may require access to all saved
> registers. We only save those registers not preserved by C code
> currently.
>
> Provide a special syscall entry for exit and exit_group syscalls
> similar to that used by clone and clone3, which have the same
> requirements.
>
> No fix to io_uring appears to be needed, because m68k copy_thread
> treats kernel threads the same as e.g. alpha does, and copies only
> a subset of registers in that case.
>
> CC: Eric W. Biederman <ebiederm@xmission.com>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> CC: Andreas Schwab <schwab@linux-m68k.org>
> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
> ---
>  arch/m68k/kernel/entry.S              | 14 ++++++++++++++
>  arch/m68k/kernel/process.c            | 16 ++++++++++++++++
>  arch/m68k/kernel/syscalls/syscall.tbl |  4 ++--
>  3 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
> index 9dd76fb..1e067e6 100644
> --- a/arch/m68k/kernel/entry.S
> +++ b/arch/m68k/kernel/entry.S
> @@ -76,6 +76,20 @@ ENTRY(__sys_clone3)
>  	lea	%sp@(28),%sp
>  	rts
>
> +ENTRY(__sys_exit)
> +	SAVE_SWITCH_STACK
> +	pea	%sp@(SWITCH_STACK_SIZE)
> +	jbsr	m68k_exit
> +	lea	%sp@(28),%sp
> +	rts
> +
> +ENTRY(__sys_exit_group)
> +	SAVE_SWITCH_STACK
> +	pea	%sp@(SWITCH_STACK_SIZE)
> +	jbsr	m68k_exit_group
> +	lea	%sp@(28),%sp
> +	rts
> +
>  ENTRY(sys_sigreturn)
>  	SAVE_SWITCH_STACK
>  	movel	%sp,%sp@-		  | switch_stack pointer
> diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
> index da83cc8..df4e5f1 100644
> --- a/arch/m68k/kernel/process.c
> +++ b/arch/m68k/kernel/process.c
> @@ -138,6 +138,22 @@ asmlinkage int m68k_clone3(struct pt_regs *regs)
>  	return sys_clone3((struct clone_args __user *)regs->d1, regs->d2);
>  }
>
> +/*
> + * Because extra registers are saved on the stack after the sys_exit()
> + * arguments, this C wrapper extracts them from pt_regs * and then calls the
> + * generic sys_exit() implementation.
> + */
> +asmlinkage int m68k_exit(struct pt_regs *regs)
> +{
> +	return sys_exit(regs->d1);
> +}
> +
> +/* Same for sys_exit_group ... */
> +asmlinkage int m68k_exit_group(struct pt_regs *regs)
> +{
> +	return sys_exit_group(regs->d1);
> +}
> +
>  int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
>  		struct task_struct *p, unsigned long tls)
>  {
> diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
> index 0dd019d..3d5b6fbc 100644
> --- a/arch/m68k/kernel/syscalls/syscall.tbl
> +++ b/arch/m68k/kernel/syscalls/syscall.tbl
> @@ -8,7 +8,7 @@
>  # The <abi> is always "common" for this file
>  #
>  0	common	restart_syscall			sys_restart_syscall
> -1	common	exit				sys_exit
> +1	common	exit				__sys_exit
>  2	common	fork				__sys_fork
>  3	common	read				sys_read
>  4	common	write				sys_write
> @@ -254,7 +254,7 @@
>  244	common	io_submit			sys_io_submit
>  245	common	io_cancel			sys_io_cancel
>  246	common	fadvise64			sys_fadvise64
> -247	common	exit_group			sys_exit_group
> +247	common	exit_group			__sys_exit_group
>  248	common	lookup_dcookie			sys_lookup_dcookie
>  249	common	epoll_create			sys_epoll_create
>  250	common	epoll_ctl			sys_epoll_ctl
>