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

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Message-ID: <ZSwAw+UyrIknsE5S@gmail.com>
Date:   Sun, 15 Oct 2023 11:09:55 -0400
From:   Guo Ren <guoren@...nel.org>
To:     Alejandro Colomar <alx@...nel.org>
Cc:     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

On Sun, Oct 15, 2023 at 01:20:42AM +0200, Alejandro Colomar wrote:
> 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.
Yeah, I've sent a patch for it; please review:
https://lore.kernel.org/linux-csky/20231015150732.1991997-1-guoren@kernel.org/

> 
> Cheers,
> Alex
> 
> > 
> > 
> > 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/
> 
> -- 
> <https://www.alejandro-colomar.es/>