[Libguestfs] nbdkit build failure (was: Re: jplesnik's nbdkit-1.35.5-4.fc39 failed to build)

Thu Jul 13 10:03:35 UTC 2023

On Thu, Jul 13, 2023 at 10:29:44AM +0100, Richard W.M. Jones wrote:
> It's a crash in Perl code, although called from the nbdkit perl plugin
> (C bindings).  Still debugging this ...
> 
> Core was generated by `/home/rjones/d/nbdkit/server/nbdkit -U /tmp/nbdkittPN34a/sock -P /tmp/nbdkittPN'.
> Program terminated with signal SIGSEGV, Segmentation fault.
> 
> warning: Section `.reg-xstate/150177' in core file too small.
> #0  Perl_my_snprintf (buffer=0x7f3a1e5fc630 "p\310_\036:\177", len=32, 
>     format=0x7f3a1ef7e322 "_<(eval %lu)")
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/util.c:5248
> Downloading source file /usr/src/debug/perl-5.38.0-499.fc39.x86_64/util.c
> 5248            WITH_LC_NUMERIC_SET_TO_NEEDED(                                  
> [Current thread is 1 (Thread 0x7f3a1e5fd6c0 (LWP 150177))]
> (gdb) bt
> #0  Perl_my_snprintf (buffer=0x7f3a1e5fc630 "p\310_\036:\177", len=32, 
>     format=0x7f3a1ef7e322 "_<(eval %lu)")
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/util.c:5248

https://github.com/Perl/perl5/blob/ff7e37d5ca2e55a1e53e5b375e3cc9aedc9ce4ec/util.c#L5248

Since its hardly obvious from the code, that macro expands to the
monster below.  I didn't bother to format it completely ...

# 5245 "util.c"
    if (retval == -1) {
        do {
	  void (*_restore_LC_NUMERIC_function)(PerlInterpreter* my_perl __attribute__((unused))) = ((void *)0);
          do { 
           _Bool _in_lc_numeric = ((( ((
             _Bool
               ) ((my_perl->Icompiling).cop_hints & 0x00000004)) || ( ((_Bool) ((my_perl->Icompiling).cop_hints & 0x00000010)) && Perl__is_in_locale_category(my_perl, (1), (
       1
       )))) || (((my_perl->Icurcop) && (((my_perl->Icurcop))->cop_hints + 0) & 0x00000004) || (((my_perl->Icurcop) && (((my_perl->Icurcop))->cop_hints + 0) & 0x00000010) && Perl__is_in_locale_category(my_perl, (0), (
       1
       ))))));
       ((void)0);
       if (_in_lc_numeric) {
         if ((! (my_perl->Inumeric_underlying) && (my_perl->Inumeric_standard) < 2)) { Perl_set_numeric_underlying(my_perl); _restore_LC_NUMERIC_function = &Perl_set_numeric_standard; }
        } else {
	  if ((! (my_perl->Inumeric_standard))) { Perl_set_numeric_standard(my_perl); _restore_LC_NUMERIC_function = &Perl_set_numeric_underlying; } }
        } while (0);
	retval = vsnprintf(buffer, len, format, ap);;
	do { if (_restore_LC_NUMERIC_function) { _restore_LC_NUMERIC_function(my_perl); } ((void)0); } while (0);
        } while (0);

... because the fundamental problem is:

(gdb) print my_perl
$13 = (PerlInterpreter *) 0x0

so that's not gonna work.

Notice the assignment of my_perl = NULL in the macro expansion.  I
think that comes from a dTHX macro, but the macros are so nested that
it's hard to tell where from.  We are creating a Perl interpreter in
our code.

I'll come up with a minimal reproducer & file a BZ.

Rich.

> #1  0x00007f3a1ed8545f in Perl_pp_entereval (my_perl=0xcb39c90)
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/pp_ctl.c:5107
> #2  0x00007f3a1ed2d5e8 in Perl_runops_standard (my_perl=0xcb39c90)
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/run.c:41
> #3  0x00007f3a1ec73ddc in Perl_eval_sv (my_perl=my_perl at entry=0xcb39c90, 
>     sv=sv at entry=0xcb3d2b8, flags=flags at entry=2)
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/perl.c:3269
> #4  0x00007f3a1ec740e0 in Perl_eval_pv (my_perl=0xcb39c90, p=<optimized out>, 
>     croak_on_error=croak_on_error at entry=0)
>     at /usr/src/debug/perl-5.38.0-499.fc39.x86_64/perl.c:3359
> #5  0x00007f3a1fc9e6ca in callback_defined (
>     perl_func_name=perl_func_name at entry=0x7f3a1fca21af "can_write")
>     at /home/rjones/d/nbdkit/plugins/perl/perl.c:102
> #6  0x00007f3a1fc9f28c in perl_boolean (handle=0xcb7a350, 
>     callback_name=0x7f3a1fca21af "can_write", fn_name=0x7f3a1fca21b3 "write")
>     at /home/rjones/d/nbdkit/plugins/perl/perl.c:430
> #7  0x000000000040e290 in plugin_can_write (c=<optimized out>) at plugins.c:488
> #8  0x00000000004078fe in backend_can_write (c=0x7f3a18000fb0) at backend.c:462
> #9  0x0000000000410ea9 in protocol_common_open (
>     exportsize=exportsize at entry=0x7f3a1e5fca00, 
>     flags=flags at entry=0x7f3a18000e84, 
>     exportname=exportname at entry=0x7f3a18000f90 "") at protocol-handshake.c:103
> #10 0x00000000004112ab in finish_newstyle_options (
>     exportsize=exportsize at entry=0x7f3a1e5fca00, exportname_in=<optimized out>, 
>     exportnamelen=exportnamelen at entry=0) at protocol-handshake-newstyle.c:319
> #11 0x00000000004125e1 in negotiate_handshake_newstyle_options ()
>     at protocol-handshake-newstyle.c:619
> #12 protocol_handshake_newstyle () at protocol-handshake-newstyle.c:985
> #13 0x0000000000410e15 in protocol_handshake () at protocol-handshake.c:55
> #14 0x000000000040a474 in handle_single_connection (sockin=6, 
>     sockout=<optimized out>) at connections.c:180
> #15 0x0000000000414baf in start_thread (datav=0xcb2c4f0) at sockets.c:377
> #16 0x00007f3a1f68db37 in start_thread (arg=<optimized out>)
>     at pthread_create.c:444
> #17 0x00007f3a1f714bec in clone3 ()
>     at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
> 
> Rich.
> 
> -- 
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> nbdkit - Flexible, fast NBD server with plugins
> https://gitlab.com/nbdkit/nbdkit

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
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