[PATCHv2 0/2] clone: Support passing tls argument via C rather than pt_regs magic

[PATCHv2 0/2] clone: Support passing tls argument via C rather than pt_regs magic

[Josh Triplett]

clone has some of the quirkiest syscall handling in the kernel, with a pile of
special cases, historical curiosities, and architecture-specific calling
conventions.  In particular, clone with CLONE_SETTLS accepts a parameter "tls"
that the C entry point completely ignores and some assembly entry points
overwrite; instead, the low-level arch-specific code pulls the tls parameter
out of the arch-specific register captured as part of pt_regs on entry to the
kernel.  That's a massive hack, and it makes the arch-specific code only work
when called via the specific existing syscall entry points; because of this
hack, any new clone-like system call would have to accept an identical tls
argument in exactly the same arch-specific position, rather than providing a
unified system call entry point across architectures.

The first patch allows architectures to handle the tls argument via normal C
parameter passing, if they opt in by selecting HAVE_COPY_THREAD_TLS.  The
second patch makes 32-bit and 64-bit x86 opt into this.

These two patches came out of the clone4 series, which isn't ready for this
merge window, but these first two cleanup patches were entirely uncontroversial
and have acks.  I'd like to go ahead and submit these two so that other
architectures can begin building on top of this and opting into
HAVE_COPY_THREAD_TLS.  However, I'm also happy to wait and send these through
the next merge window (along with v3 of clone4) if anyone would prefer that.

v2: Move co-author from signoffs to a note in the commit message, as
    required by Ingo Molnar.

Josh Triplett (2):
  clone: Support passing tls argument via C rather than pt_regs magic
  x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit

 arch/Kconfig                 |  7 ++++++
 arch/x86/Kconfig             |  1 +
 arch/x86/ia32/ia32entry.S    |  2 +-
 arch/x86/kernel/process_32.c |  6 ++---
 arch/x86/kernel/process_64.c |  8 +++----
 include/linux/sched.h        | 14 +++++++++++
 include/linux/syscalls.h     |  6 ++---
 kernel/fork.c                | 55 +++++++++++++++++++++++++++++---------------
 8 files changed, 69 insertions(+), 30 deletions(-)

-- 
2.1.4

Re: [PATCHv2 0/2] clone: Support passing tls argument via C rather than pt_regs magic

[Ingo Molnar]

* Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org> wrote:

> clone has some of the quirkiest syscall handling in the kernel, with 
> a pile of special cases, historical curiosities, and 
> architecture-specific calling conventions.  In particular, clone 
> with CLONE_SETTLS accepts a parameter "tls" that the C entry point 
> completely ignores and some assembly entry points overwrite; 
> instead, the low-level arch-specific code pulls the tls parameter 
> out of the arch-specific register captured as part of pt_regs on 
> entry to the kernel.  That's a massive hack, and it makes the 
> arch-specific code only work when called via the specific existing 
> syscall entry points; because of this hack, any new clone-like 
> system call would have to accept an identical tls argument in 
> exactly the same arch-specific position, rather than providing a 
> unified system call entry point across architectures.
> 
> The first patch allows architectures to handle the tls argument via 
> normal C parameter passing, if they opt in by selecting 
> HAVE_COPY_THREAD_TLS.  The second patch makes 32-bit and 64-bit x86 
> opt into this.
> 
> These two patches came out of the clone4 series, which isn't ready 
> for this merge window, but these first two cleanup patches were 
> entirely uncontroversial and have acks.  I'd like to go ahead and 
> submit these two so that other architectures can begin building on 
> top of this and opting into HAVE_COPY_THREAD_TLS.  However, I'm also 
> happy to wait and send these through the next merge window (along 
> with v3 of clone4) if anyone would prefer that.
> 
> v2: Move co-author from signoffs to a note in the commit message, as
>     required by Ingo Molnar.
> 
> Josh Triplett (2):
>   clone: Support passing tls argument via C rather than pt_regs magic
>   x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit
> 
>  arch/Kconfig                 |  7 ++++++
>  arch/x86/Kconfig             |  1 +
>  arch/x86/ia32/ia32entry.S    |  2 +-
>  arch/x86/kernel/process_32.c |  6 ++---
>  arch/x86/kernel/process_64.c |  8 +++----
>  include/linux/sched.h        | 14 +++++++++++
>  include/linux/syscalls.h     |  6 ++---
>  kernel/fork.c                | 55 +++++++++++++++++++++++++++++---------------
>  8 files changed, 69 insertions(+), 30 deletions(-)

So I have no objections if Linus doesn't see a cleaner/better 
approach.

Thanks,

	Ingo