Re: Re: [PATCH V3] MIPS: Add get_thread_area syscall
From: ååä
Date: Mon Dec 16 2019 - 20:48:12 EST
Dear Paul,
Thank you very much.
I didn`t know this way asm("rdhwr %0, $29" : "=r"(*ptls)) before.Now I have a test for it and it realy can work normally.
I just find get_thread_area syscall at path arch/x86.so I have a implement on MIPS platform. And I think set_thread_area and get_thread_area is matched in pairs.
Now it seems that the get_thread_area syscall is not necessary for criu.
Thanks,
Guoyun Sun
> -----ååéä-----
> åää: "Paul Burton" <paulburton@xxxxxxxxxx>
> åéæé: 2019-12-17 03:33:33 (ææä)
> æää: "Guoyun Sun" <sunguoyun@xxxxxxxxxxx>
> æé: "Ralf Baechle" <ralf@xxxxxxxxxxxxxx>, "James Hogan" <jhogan@xxxxxxxxxx>, "Peter Zijlstra" <peterz@xxxxxxxxxxxxx>, "Christian Brauner" <christian.brauner@xxxxxxxxxx>, "Arnd Bergmann" <arnd@xxxxxxxx>, "Heiko Carstens" <heiko.carstens@xxxxxxxxxx>, "David Howells" <dhowells@xxxxxxxxxx>, "Geert Uytterhoeven" <geert@xxxxxxxxxxxxxx>, "Catalin Marinas" <catalin.marinas@xxxxxxx>, linux-mips@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, "Tiezhu Yang" <yangtiezhu@xxxxxxxxxxx>, "Xuefeng Li" <lixuefeng@xxxxxxxxxxx>
> äé: Re: [PATCH V3] MIPS: Add get_thread_area syscall
>
> Hi Guoyun,
>
> On Mon, Dec 16, 2019 at 10:17:51AM +0800, Guoyun Sun wrote:
> > CRIU(https://criu.org/) tools will dump TLS(Thread Local Storage) by
> > get_thread_area during checkpoint and restore TLS by set_thread_area during
> > restore. without this syscall, criu restore will fail on MIPS platform
> > because a variable with GCC __thread will be invalid.
> >
> > The following function will be called when criu restore
> >
> > static inline void restore_tls(tls_t *ptls) {
> > asm volatile(
> > "move $4, %0 \n"
> > "li $2, "__stringify(__NR_set_thread_area)" \n"
> > "syscall \n"
> > :
> > : "r"(*ptls)
> > : "$4","$2","memory");
> >
> > the *ptls can be obtained by get_thread_area on MIPS platform when criu
> > checkpoint. just like this:
> >
> > static inline void arch_get_tls(tls_t *ptls)
> > {
> > asm volatile(
> > "move $4, %0 \n"
> > "li $2, "__stringify(__NR_get_thread_area)" \n"
> > "syscall \n"
> > :
> > : "r"(ptls)
> > : "$4","$2","memory");
> >
> > }
>
> Why would you need a syscall for this?
>
> Why not retrieve the value using the rdhwr instruction just like every
> other bit of code using thread-local storage does?
>
> ie. something like:
>
> static inline void arch_get_tls(tls_t *ptls)
> {
> asm("rdhwr %0, $29" : "=r"(*ptls));
> }
>
> Thanks,
> Paul
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