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

From: Ingo Molnar
Date: Tue May 12 2015 - 03:02:49 EST

* Josh Triplett <josh@xxxxxxxxxxxxxxxx> 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


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