From: Paul Burton <paulburton@kernel.org>
To: Guoyun Sun <sunguoyun@loongson.cn>
Cc: Ralf Baechle <ralf@linux-mips.org>,
James Hogan <jhogan@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Christian Brauner <christian.brauner@ubuntu.com>,
Arnd Bergmann <arnd@arndb.de>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
David Howells <dhowells@redhat.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
Tiezhu Yang <yangtiezhu@loongson.cn>,
Xuefeng Li <lixuefeng@loongson.cn>
Subject: Re: [PATCH V3] MIPS: Add get_thread_area syscall
Date: Mon, 16 Dec 2019 11:33:33 -0800 [thread overview]
Message-ID: <20191216193333.up4qqzxno23pbzix@lantea.localdomain> (raw)
In-Reply-To: <1576462671-7226-1-git-send-email-sunguoyun@loongson.cn>
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
next prev parent reply other threads:[~2019-12-16 19:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 2:17 [PATCH V3] MIPS: Add get_thread_area syscall Guoyun Sun
2019-12-16 19:33 ` Paul Burton [this message]
2019-12-17 1:47 ` 孙国云
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