Re: [PATCH] Tests for minimal signal handler functionality in MINSIGSTKSZ space.

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Jan 18, 2019 at 10:08 AM Zack Weinberg <zackw@panix.com> wrote:
>
> On Fri, Jan 18, 2019 at 11:40 AM Carlos O'Donell <carlos@redhat.com> wrote:
> >
> > All of this raises an interesting point. Should MINSIGSTKSZ
> > have included enough space for the lazy resolution to happen?
> > I think we have to, because you're never going to have already
> > called abort, quick_exit, or _exit, so they will all go through
> > lazy binding resolution if you're not BIND_NOW. Which means we
> > need an average estimate from all arches about the lazy binding
> > stack usage.
>
> in the long term, this strikes me as another reason we should be
> thinking about making eager symbol resolution the default ... (and
> then we could start thinking about moving the dynamic loader out of
> process ...)
>
> in the medium term, though, I completely agree
>
> in the 2.29 term, though, perhaps the best we can do is some
> documentation, I'll have a go at writing that in the next couple days
>

The 32-bit signal/tst-minsigstksz-1 failed on AVX512 machine:

Program received signal SIGSEGV, Segmentation fault.
0xf7e2e366 in __GI___libc_sigaction (sig=10, act=0xf7cf70a8, oact=0xf7cf7134)
    at ../sysdeps/unix/sysv/linux/sigaction.c:48
48   if (act)
(gdb) disass
Dump of assembler code for function __GI___libc_sigaction:
   0xf7e2e350 <+0>: sub    $0x14c,%esp
   0xf7e2e356 <+6>: xor    %ecx,%ecx
   0xf7e2e358 <+8>: mov    %esi,0x140(%esp)
   0xf7e2e35f <+15>: mov    0x154(%esp),%edx
=> 0xf7e2e366 <+22>: call   0xf7f44c2f <__x86.get_pc_thunk.si>

For 64-bit:

Breakpoint 3, __GI___libc_sigaction (sig=sig@entry=10,
    act=act@entry=0x7fffffffdb40, oact=oact@entry=0x0)
    at ../sysdeps/unix/sysv/linux/sigaction.c:48
48   if (act)
(gdb) disass
Dump of assembler code for function __GI___libc_sigaction:
=> 0x00007ffff7e4dc50 <+0>: sub    $0xd0,%rsp
   0x00007ffff7e4dc57 <+7>: mov    %rdx,%r8
   0x00007ffff7e4dc5a <+10>: test   %rsi,%rsi
   0x00007ffff7e4dc5d <+13>: je     0x7ffff7e4ddb0 <__GI___libc_sigaction+352>
   0x00007ffff7e4dc63 <+19>: mov    (%rsi),%rax

64-bit allocates smaller stack and it doesn't need to call
__x86.get_pc_thunk.si.  On AVX512, kernel needs larger
stack space to save signal context.

-- 
H.J.