Re: sigprocmask.c appears to be incompatible w/ system headers

[Godfrey, Keith]

Hi Bruno,

Thank you for quick the response.

> There is no sigprocmask.lo in this list. This is normal; gnulib's sigprocmask.c
> is not compiled on glibc systems. You can see from the gnulib documentation
> <http://www.gnu.org/software/gnulib/manual/html_node/sigprocmask.html>
> that this source file is only compiled on mingw platforms.
>    

Indeed. Placing an "#error" line in sigprocmask.cc did not disrupt the 
build.


> Also, the generated signal.h is built with HAVE_SIGSET_T being replaced with 1,
> therefore it does not redefine the 'sigset_t' type.
>
> In<https://savannah.gnu.org/bugs/?30685>  you write:
>    
> > A change (similar to Leonardo's) that seems to work while theoretically 
> > maintaining sigaction
> > functionality is to explicitly call the sigemptyset macro (bits/sigset.h):
> >
> > octave-3.4.0/src/sighandlers.cc line 225
> >   //gnulib::sigemptyset (&act.sa_mask);
> >   //gnulib::sigemptyset (&oact.sa_mask);
> >   //gnulib::sigaction (sig,&act,&oact);
> >   __sigemptyset (&act.sa_mask);
> >   __sigemptyset (&oact.sa_mask);
> >   sigaction (sig,&act,&oact);
> >
> > (only removing the namespace didn't work for me either)
> >      
> This indicates that the crucial difference is between the __sigemptyset
> macro and the sigemptyset functions, both from glibc.
>    

This report might be misleading, and there might not be a difference. 
When I removed the gnulib namespace from the file entirely, and 
recompiled, octave started and ran. The problem with this report was 
that there were still some instances of "gnulib::" on other function 
calls. I suspect this was also the case when others removed "gnulib" on 
sigemptyset and it still crashed (presumably on the subsequent 
gnulib::sigaction).


> Or if 'sigemptyset' would work fine, then the crucial difference would
> be in the function pointer indirection by which gnulib implements the
> 'gnulib::sigemptyset' function in term of the 'sigemptyset' function
> pointer.
>    

> In order to debug this, I would recommend to look at
>
>    - the source code of the __sigemptyset macro and of the sigemptyset
>      function,
>    

From /usr/include/bits/sigset.h

# define _SIGSET_NWORDS (1024 / (8 * sizeof (unsigned long int)))
typedef struct
  {
    unsigned long int __val[_SIGSET_NWORDS];
  } __sigset_t;


#  define __sigemptyset(set) \
  (__extension__ ({ int __cnt = _SIGSET_NWORDS;                   \
            sigset_t *__set = (set);                      \
            while (--__cnt >= 0) __set->__val[__cnt] = 0;         \
            0; }))

I am unable to find source code for the sigemptyset function of glibc.


>    - the assembly level instructions where it crashes:
>
>       #0  0xb785896c in sigemptyset () from 
> /home/muttoni/a/octave-3.3.53/src/.libs/liboctinterp-3.3.53.so
>
>      because it's not clear why liboctinterp-3.3.53.so would contain
>      a sigemptyset function at all (since gnulib's one is not being
>      compiled).
>    

This is naive speculation, but perhaps liboctinterp is involved because 
"gnulib::sigemptyset" is being called, instead of simply "sigemptyset"? 
As mentioned above, I removed all references of "gnulib::" from the 
problem file and recompiled, and it seemed to run fine. With the 
namespace declared, it reliably crashes. Perhaps a link issue? This 
speculation is discrepant with reports in the original octave bug, but 
in those cases people (seem to have) only removed "gnulib::" from 
sigemptyset, leaving the other instances intact. If I do that, it does 
crash.


Assembly instructions at breakpoint shortly before crash. Crash occurs 
stepping past instruction at 0x2b630861baff.

Breakpoint 1, octave_set_signal_handler (sig=2,
    handler=0x2b630861c080 <sigint_handler>, restart_syscalls=true)
    at sighandlers.cc:206
206      act.sa_flags = 0;
2: x/10i $pc
0x2b630861bae3 <_Z25octave_set_signal_handleriPFviEb+35>:
---Type <return> to continue, or q <return> to quit---
    movl   $0x0,0x128(%rsp)
0x2b630861baee <_Z25octave_set_signal_handleriPFviEb+46>:
    je     0x2b630861bb50 <_Z25octave_set_signal_handleriPFviEb+144>
0x2b630861baf0 <_Z25octave_set_signal_handleriPFviEb+48>:    test   %dl,%dl
0x2b630861baf2 <_Z25octave_set_signal_handleriPFviEb+50>:
    je     0x2b630861baff <_Z25octave_set_signal_handleriPFviEb+63>
0x2b630861baf4 <_Z25octave_set_signal_handleriPFviEb+52>:
    movl   $0x10000000,0x128(%rsp)
0x2b630861baff <_Z25octave_set_signal_handleriPFviEb+63>:
    lea    0xa0(%rsp),%r12
0x2b630861bb07 <_Z25octave_set_signal_handleriPFviEb+71>:
    lea    0x8(%r12),%rdi
0x2b630861bb0c <_Z25octave_set_signal_handleriPFviEb+76>:
    callq  0x2b630905ede8 <sigemptyset>
0x2b630861bb11 <_Z25octave_set_signal_handleriPFviEb+81>:
    lea    0x8(%rsp),%rdi
0x2b630861bb16 <_Z25octave_set_signal_handleriPFviEb+86>:
    callq  0x2b630905ede8 <sigemptyset>
1: x/3i $pc
0x2b630861bae3 <_Z25octave_set_signal_handleriPFviEb+35>:
    movl   $0x0,0x128(%rsp)
0x2b630861baee <_Z25octave_set_signal_handleriPFviEb+46>:
    je     0x2b630861bb50 <_Z25octave_set_signal_handleriPFviEb+144>
---Type <return> to continue, or q <return> to quit---
0x2b630861baf0 <_Z25octave_set_signal_handleriPFviEb+48>:    test   %dl,%dl
Current language:  auto; currently c++
(gdb)
-------------------------------------


Assembly instructions at crash
(gdb) s

Program received signal SIGSEGV, Segmentation fault.
0x00002b630905ede8 in sigemptyset ()
   from 
/global/home/keith/software/octave-3.4.0/src/.libs/liboctinterp-3.4.0.so
2: x/10i $pc
0x2b630905ede8 <sigemptyset>:    callq  0x2b636c0ef3da
0x2b630905eded <sigemptyset+5>:    sub    (%rax),%eax
0x2b630905edef <sigemptyset+7>:    add    %dh,%al
0x2b630905edf1 <sigaction+1>:    in     (%dx),%eax
0x2b630905edf2 <sigaction+2>:    add    $0x2b6309,%eax
0x2b630905edf7 <sigaction+7>:    add    %bh,%al
0x2b630905edf9 <sigaddset+1>:    in     (%dx),%eax
0x2b630905edfa <sigaddset+2>:    add    $0x2b6309,%eax
0x2b630905edff <sigaddset+7>:    add    %al,(%rax)
0x2b630905ee01 <sigprocmask+1>:    out    %al,(%dx)
1: x/3i $pc
0x2b630905ede8 <sigemptyset>:    callq  0x2b636c0ef3da
0x2b630905eded <sigemptyset+5>:    sub    (%rax),%eax
0x2b630905edef <sigemptyset+7>:    add    %dh,%al
(gdb)


>    - the preprocessed source file (g++ -E -dD) of the compilation unit
>      that contains the gnulib::sigemptyset invocation.
>    

It's beyond my mental capacity right now to parse the make command and 
set up the proper environment to do this manually. I've attached make 
output that includes "sighandlers", in case that might be of help. If 
it's necessary, I can try to get preprocessor output.

Keith

> Bruno
>

sighandler.txt
Description: Text document