On Sun, Sep 25, 2016 at 09:03:07PM +0200, Michael Kerrisk (man-pages) wrote: > On 09/04/2016 07:11 AM, Josh Triplett wrote: > > On Sun, Sep 04, 2016 at 04:30:44PM +1200, Michael Kerrisk (man-pages) wrote: > >> [CC += Josh] > >> > >> Josh, I know you were submitting patches relate to the clone() TLS argument a > >> while back. Could you comment on this patch proposal below (also > >> https://bugzilla.kernel.org/show_bug.cgi?id=118241 is relevant). > > > > Sure. > > > >> On 08/24/2016 03:06 PM, Keno Fischer wrote: > >>> The prototype for the system call was added in 81f10dad, but looking at the > >>> kernel's fork.c, I believe the relevant definition is > >>> > >>> SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp, > >>> int __user *, parent_tidptr, > >>> int __user *, child_tidptr, > >>> unsigned long, tls) > >>> > >>> so the last argument is the tls argument, not a pt_regs argument. > >>> I stumbled upon this while trying to understand CLONE_SETTLS, so I expanded > >>> that description a little to cover other architectures. > > > > This description and patch looks correct to me. > > Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > Thanks, Josh. > > > Ideally, I'd suggest a follow-up patch to improve the prototypes for the > > various architectures. Rather than saying "x86 looks roughly this way, > > on these architectures swap these arguments, on these architectures > > ...", I'd suggest explicitly giving each of the four prototypes (normal, > > CONFIG_CLONE_BACKWARDS, CONFIG_CLONE_BACKWARDS2, > > CONFIG_CLONE_BACKWARDS3) and the corresponding architectures. > > I applied the patch below. Okay? Mostly looks good, but one comment below. > diff --git a/man2/clone.2 b/man2/clone.2 > index 5c1e301..26c6b30 100644 > --- a/man2/clone.2 > +++ b/man2/clone.2 > @@ -54,11 +54,7 @@ clone, __clone2 \- create a child process > .BI " /* pid_t *" ptid ", void *" newtls \ > ", pid_t *" ctid " */ );" > > -/* Prototype for the raw system call */ > - > -.BI "long clone(unsigned long " flags ", void *" child_stack , > -.BI " int *" ptid ", int *" ctid , > -.BI " unsigned long " newtls ); > +/* For the prototype of the raw system call, see NOTES */ > .fi > .SH DESCRIPTION > .BR clone () > @@ -821,16 +817,58 @@ arguments of the > .BR clone () > wrapper function are omitted. > Furthermore, the argument order changes. > -The raw system call interface on x86 and many other architectures is roughly: > +In addition, there are variations across architectures. > + > +The raw system call interface on x86-64 and some other architectures > +(including sh, tile, and alpha) is roughly: > + > .in +4 > .nf > +.BI "long clone(unsigned long " flags ", void *" child_stack , > +.BI " int *" ptid ", int *" ctid , > +.BI " unsigned long " newtls ); > +.fi > +.in > + > +On x86-32, and several other common architectures > +(including score, microblaze, ARM, ARM 64, PA-RISC, arc, Power PC, xtensa, > +and MIPS), > +.\" CONFIG_CLONE_BACKWARDS > +the order of the last two arguments is reversed: > > +.in +4 > +.nf > .BI "long clone(unsigned long " flags ", void *" child_stack , > +.BI " int *" ptid ", unsigned long " newtls , > +.BI " int *" ctid ); > +.fi > +.in > + > +On the cris and s390 architectures, > +.\" CONFIG_CLONE_BACKWARDS2 > +the order of the first two arguments is reversed: > + > +.in +4 > +.nf > +.BI "long clone(void *" child_stack ", unsigned long " flags , > .BI " int *" ptid ", int *" ctid , > .BI " unsigned long " newtls ); > +.fi > +.in > + > +On the microblaze architecture, > +.\" CONFIG_CLONE_BACKWARDS3 > +an additional argument is supplied: This mentions microblaze twice: one in CONFIG_CLONE_BACKWARDS and again here. And I don't see IA-64 mentioned anywhere. > +.in +4 > +.nf > +.BI "long clone(unsigned long " flags ", void *" child_stack , > +.BI " int " stack_size , "\fR /* Size of stack */" > +.BI " int *" ptid ", int *" ctid , > +.BI " unsigned long " newtls ); > .fi > .in > + > Another difference for the raw system call is that the > .I child_stack > argument may be zero, in which case copy-on-write semantics ensure that the > @@ -839,15 +877,11 @@ the stack. > In this case, for correct operation, the > .B CLONE_VM > option should not be specified. > - > -For some architectures, the order of the arguments for the system call > -differs from that shown above. > -On the score, microblaze, ARM, ARM 64, PA-RISC, arc, Power PC, xtensa, > -and MIPS architectures, > -the order of the fourth and fifth arguments is reversed. > -On the cris and s390 architectures, > -the order of the first and second arguments is reversed. > +.\" > .SS blackfin, m68k, and sparc > +.\" Mike Frysinger noted in a 2013 mail: > +.\" these arches don't define __ARCH_WANT_SYS_CLONE: > +.\" blackfin ia64 m68k sparc > The argument-passing conventions on > blackfin, m68k, and sparc are different from the descriptions above. > For details, see the kernel (and glibc) source. > > > -- > Michael Kerrisk > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
