linux-kernel - Re: set_thread_area.2: csky architecture undocumented

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Date:   Tue, 24 Nov 2020 20:07:07 +0800
From:   Guo Ren <guoren@...nel.org>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>,
        linux-man <linux-man@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-csky@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: set_thread_area.2: csky architecture undocumented

Thx Michael & Alejandro,

Yes, the man page has no csky's.

C-SKY have abiv1 and abiv2
For abiv1: There is no register for tls saving, We use trap 3 to got
tls and use set_thread_area to init ti->tp_value.
For abiv2: The r31 is the tls register. We could directly read r31 to
got r31 and use set_thread_area to init reg->tls value.

In glibc:
# ifdef __CSKYABIV2__
/* Define r31 as thread pointer register.  */
#  define READ_THREAD_POINTER() \
        mov r0, r31;
# else
#  define READ_THREAD_POINTER() \
        trap 3;
# endif

/* Code to initially initialize the thread pointer.  This might need
   special attention since 'errno' is not yet available and if the
   operation can cause a failure 'errno' must not be touched.  */
# define TLS_INIT_TP(tcbp) \
  ({ INTERNAL_SYSCALL_DECL (err);                                       \
     long result_var;                                                   \
     result_var = INTERNAL_SYSCALL (set_thread_area, err, 1,            \
                    (char *) (tcbp) + TLS_TCB_OFFSET);                  \
     INTERNAL_SYSCALL_ERROR_P (result_var, err)                         \
       ? "unknown error" : NULL; })

In kernel:
SYSCALL_DEFINE1(set_thread_area, unsigned long, addr)
{
        struct thread_info *ti = task_thread_info(current);
        struct pt_regs *reg = current_pt_regs();

        reg->tls = addr;
        ti->tp_value = addr;

        return 0;
}

Any comments are welcome :)


On Tue, Nov 24, 2020 at 5:51 PM Michael Kerrisk (man-pages)
<mtk.manpages@...il.com> wrote:
>
> Hi Alex,
>
> On 11/23/20 10:31 PM, Alejandro Colomar (man-pages) wrote:
> > Hi Michael,
> >
> > SYNOPSIS
> >        #include <linux/unistd.h>
> >
> >        #if defined __i386__ || defined __x86_64__
> >        # include <asm/ldt.h>
> >
> >        int get_thread_area(struct user_desc *u_info);
> >        int set_thread_area(struct user_desc *u_info);
> >
> >        #elif defined __m68k__
> >
> >        int get_thread_area(void);
> >        int set_thread_area(unsigned long tp);
> >
> >        #elif defined __mips__
> >
> >        int set_thread_area(unsigned long addr);
> >
> >        #endif
> >
> >        Note: There are no glibc wrappers for these system  calls;  see
> >        NOTES.
> >
> >
> > $ grep -rn 'SYSCALL_DEFINE.*et_thread_area'
> > arch/csky/kernel/syscall.c:6:
> > SYSCALL_DEFINE1(set_thread_area, unsigned long, addr)
> > arch/mips/kernel/syscall.c:86:
> > SYSCALL_DEFINE1(set_thread_area, unsigned long, addr)
> > arch/x86/kernel/tls.c:191:
> > SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, u_info)
> > arch/x86/kernel/tls.c:243:
> > SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, u_info)
> > arch/x86/um/tls_32.c:277:
> > SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
> > arch/x86/um/tls_32.c:325:
> > SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
> >
> >
> > See kernel commit 4859bfca11c7d63d55175bcd85a75d6cee4b7184
> >
> >
> > I'd change
> > -      #elif defined __mips__
> > +      #elif defined(__mips__ || __csky__)
> >
> > and then change the rest of the text to add csky when appropriate.
> > Am I correct?
>
> AFAICT, you are correct. I think the reason that csky is missing is
> that the architecture was added after this manual pages was added.
>
> Thanks,
>
> Michael
>
>
> --
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/



--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/