Re: PowerPC SIGSTKSZ

["Ryan S. Arnold" <ryan dot arnold at gmail dot com>]

On Thu, Aug 8, 2013 at 11:56 PM, Alan Modra <amodra@gmail.com> wrote:
> This copies the sparc version of sigstack.h, which gives powerpc
> #define MINSIGSTKSZ     4096
> #define SIGSTKSZ        16384
>
> Before the VSX changes, struct rt_sigframe size was 1920 plus 128 for
> __SIGNAL_FRAMESIZE giving ppc64 exactly the default MINSIGSTKSZ of
> 2048.
>
> After VSX, ucontext increased by 256 bytes.  Oops, we're over
> MINSIGSTKSZ, so powerpc has been using the wrong value for quite a
> while.  Add another ucontext for TM and rt_sigframe is now at 3872,
> giving actual MINSIGSTKSZ of 4000.
>
> The glibc testcase that I was looking at was tst-cancel21, which
> allocates 2*SIGSTKSZ (not because the test is trying to be
> conservative, but because the test actually has nested signal stack
> frames).  We blew the allocation by 48 bytes when using current
> mainline gcc to compile glibc (le ppc64).
>
> The required stack depth in _dl_lookup_symbol_x from the top of the
> next signal frame was 10944 bytes.  I guess you'd want to add 288 to
> that, implying an actual SIGSTKSZ of 11232.
>
>         * sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h: New file.
>
> diff --git a/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h b/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h
> new file mode 100644
> index 0000000..33be9e8
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h
> @@ -0,0 +1,54 @@
> +/* sigstack, sigaltstack definitions.
> +   Copyright (C) 1998-2013 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#ifndef _SIGNAL_H
> +# error "Never include this file directly.  Use <signal.h> instead"
> +#endif
> +
> +
> +/* Structure describing a signal stack (obsolete).  */
> +struct sigstack
> +  {
> +    void *ss_sp;               /* Signal stack pointer.  */
> +    int ss_onstack;            /* Nonzero if executing on this stack.  */
> +  };
> +
> +
> +/* Possible values for `ss_flags.'.  */
> +enum
> +{
> +  SS_ONSTACK = 1,
> +#define SS_ONSTACK     SS_ONSTACK
> +  SS_DISABLE
> +#define SS_DISABLE     SS_DISABLE
> +};
> +
> +/* Minimum stack size for a signal handler.  */
> +#define MINSIGSTKSZ    4096
> +
> +/* System default stack size.  */
> +#define SIGSTKSZ       16384
> +
> +
> +/* Alternate, preferred interface.  */
> +typedef struct sigaltstack
> +  {
> +    void *ss_sp;
> +    int ss_flags;
> +    size_t ss_size;
> +  } stack_t;

I tested a version of this as well for PowerPC.  Please commit this.
I'd like to have this backported to glibc 2.17 glibc 2.18.

Ryan S. Arnold