[Gcl-devel] Re: libc6.1 signal handling bug on alpha

[Paul Slootman]

On Tue 24 Feb 2004, Camm Maguire wrote:

> Greetings!  Just wondering if I should cripple gcl/maxima/acl2/axiom
> on alpha to work around this bug, or if its going to get fixed
> sometime soon.....

Don't hold your breath... :-(
I don't expect that a kernel change would be responsible for this;
my alpha is still running 2.4.19-rc2 (the latest at the time of last
boot :-) and I guess you see the same problem there. Perhaps some libc
change?

Paul Slootman

> =============================================================================
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=221969
> =============================================================================
> 
>     * To: address@hidden, address@hidden,address@hidden
>     * Subject: Apparent signal handling errors recently introduced
>     * From: Camm Maguire <address@hidden>
>     * Date: Fri, 06 Feb 2004 12:15:02 -0500
>     * Message-id: <address@hidden>
>     * Old-return-path: <address@hidden>
> 
> Greetings!  GCL and its compiled programs (maxima, acl2, axiom) can
> make use of a more efficient garbage collection algorithm by
> mprotecting certain pages read only, trapping segmentation faults, and
> then reprotecting the pages read write as necessary.  This has been
> working on alpha for a long time.  acl2 in particular was last build
> on 20021210 on lully successfully using this mechanism.  I've made
> some minor modifications to the acl2 package, and now the build breaks
> on alpha only, apparently.
> 
> Debugging on escher shows that apparently the stack is damaged in such
> a way as the program cannot determine where to return after the signal
> handler, in particular the return is one stack level up from where the
> segmentation signal was caught.  Is there any recent kernel change
> that could have caused this?
> 
> Here is a gdb session:
> 
> Starting program: /home/camm/acl2-2.7/raw_nsaved_acl2 
> /home/camm/gcl-2.6.1/unixport/ <init_nsaved_acl2.lsp
> GCL (GNU Common Lisp)  April 1994  131072 pages
> Building symbol table for /home/camm/acl2-2.7/raw_nsaved_acl2 ..
> loading /home/camm/gcl-2.6.1/unixport/../lsp/gcl_export.lsp
> ...
> [GC for 5242 RELOCATABLE-BLOCKS pages..(T=764).GC finished]
> [SGC on]
> Program received signal SIGSEGV, Segmentation fault.
> 0x0000000120667b8c in LI20 (V83=0x120d74570) at gcl_sloop.c:530
> 530           bds_bind(VV[34],(V83));
> (gdb) bt 5
> #0  0x0000000120667b8c in LI20 (V83=0x120d74570) at gcl_sloop.c:530
> #1  0x0000000120666ad8 in L7 () at gcl_sloop.c:230
> #2  0x00000001204eb984 in funcall (fun=0x120b51380) at eval.c:173
> #3  0x00000001205336ac in IapplyVector (fun=0x120b51380, nargs=2, 
>     base=0x12084ea10) at nfunlink.c:239
> #4  0x00000001204ef2f8 in fLfuncall (fun=0x120b51380) at eval.c:1140
> (More stack frames follow...)
> (gdb) up
> #1  0x0000000120666ad8 in L7 () at gcl_sloop.c:230
> 230           base[3]= (*(LnkLI247))(base[2]);
> (gdb) p base
> $35 = (object *) 0x12084ea10
> (gdb) p &base
> $36 = (object **) 0x11fffe6f8
> (gdb) c
> Continuing.
> 
> Breakpoint 1, memprotect_handler (sig=11, code=4831830752, scp=0x11fffe360, 
>     addr=0x0) at sgbc.c:1404
> 1404    int j=page_multiple;
> (gdb) p *(object **) 0x11fffe6f8
> $37 = (union lispunion **) 0x12084ea10
> (gdb) display *(object **) 0x11fffe6f8
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) n
> 1408    faddr=GET_FAULT_ADDR(sig,code,scp,addr); 
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1409    debug_fault = (long) faddr;
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1413    if (faddr >= core_end || (unsigned long)faddr < DBEGIN) {
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1422    p = page(faddr);
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1423    p = ROUND_DOWN_PAGE_NO(p);
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1424    if (p >= first_protectable_page
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1433      mprotect(pagetochar(p),page_multiple * PAGESIZE, PROT_READ_WRITE);
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1434      while (--j >= 0)
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) p j
> $38 = 1
> (gdb) n
> 1435        sgc_type_map[p+j] = sgc_type_map[p+j] | SGC_TEMP_WRITABLE;
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1434      while (--j >= 0)
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) 
> 1457  }
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) bt
> #0  memprotect_handler (sig=11, code=4831830752, scp=0x11fffe360, addr=0x0)
>     at sgbc.c:1457
> #1  0x000002000022c858 in __open_catalog () from /lib/libc.so.6.1
> #2  0x0000000120666ad8 in L7 () at gcl_sloop.c:230
> (gdb) c
> Continuing.
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x0000000120666ae4 in L7 () at gcl_sloop.c:230
> 230           base[3]= (*(LnkLI247))(base[2]);
> 1: *(union lispunion ***) 4831831800 = (union lispunion **) 0x12084ea10
> (gdb) bt
> #0  0x0000000120666ae4 in L7 () at gcl_sloop.c:230
> (gdb) p &base
> $39 = (object **) 0x12080b74c
> (gdb) p base[0]
> Cannot access memory at address 0x20add6c800000000
> (gdb)