linux-kernel - Re: [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD

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Date:	Fri, 13 Mar 2015 15:01:16 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Thiago Macieira <thiago.macieira@...el.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH 2/6] x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit
 and 64-bit

On Thu, Mar 12, 2015 at 6:40 PM, Josh Triplett <josh@...htriplett.org> wrote:
> For 32-bit userspace on a 64-bit kernel, this requires modifying
> stub32_clone to actually swap the appropriate arguments to match
> CONFIG_CLONE_BACKWARDS, rather than just leaving the C argument for tls
> broken.
>
> Signed-off-by: Josh Triplett <josh@...htriplett.org>
> Signed-off-by: Thiago Macieira <thiago.macieira@...el.com>
> ---
>  arch/x86/Kconfig             | 1 +
>  arch/x86/ia32/ia32entry.S    | 2 +-
>  arch/x86/kernel/process_32.c | 6 +++---
>  arch/x86/kernel/process_64.c | 8 ++++----
>  4 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index b7d31ca..4960b0d 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -124,6 +124,7 @@ config X86
>         select MODULES_USE_ELF_REL if X86_32
>         select MODULES_USE_ELF_RELA if X86_64
>         select CLONE_BACKWARDS if X86_32
> +       select HAVE_COPY_THREAD_TLS
>         select ARCH_USE_BUILTIN_BSWAP
>         select ARCH_USE_QUEUE_RWLOCK
>         select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index 156ebca..0286735 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -487,7 +487,7 @@ GLOBAL(\label)
>         ALIGN
>  GLOBAL(stub32_clone)
>         leaq sys_clone(%rip),%rax
> -       mov     %r8, %rcx
> +       xchg %r8, %rcx
>         jmp  ia32_ptregs_common

Do I understand correct that whatever function this is a stub for just
takes its arguments in the wrong order?  If so, can we just fix it
instead of using xchg here?

In general, I much prefer C code to new asm where it makes sense to
make this tradeoff.

Other than that, this is a huge improvement.  You'll have minor
conflicts against -tip, though.

--Andy
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