Re: set_thread_area.2: csky architecture undocumented

[Alejandro Colomar <alx@kernel.org>]

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Hi Guo,

On Tue, Nov 24, 2020 at 08:07:07PM +0800, Guo Ren wrote:

Huh, 3 years already!  I've had this in my head for all this time; just
didn't find the energy to act on it.

> Thx Michael & Alejandro,
> 
> Yes, the man page has no csky's.

I've applied a patch to add initial documentation for it:
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=a63979eb24aaf73f4be5799cc9579f84a3874b7d>

> 
> 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 :)

I'm sorry, but I have little understanding of this syscall, and that
shounds like gibberish to me :)

Feel free to send a patch to improve the documentation for csky.

Cheers,
Alex

> 
> 
> On Tue, Nov 24, 2020 at 5:51 PM Michael Kerrisk (man-pages)
> <mtk.manpages@gmail.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/

-- 
<https://www.alejandro-colomar.es/>

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