[Gcl-devel] Re: Sparc mprotect bug

[Camm Maguire]

Greetings!  BTW, your mail to gcl-devel is bouncing because its a
suscriber only list.  Can I subscribe you, or can you do so yourself,
as I almost missed your mail (it was in the administrative reject
'folder'). 

I don't think this SGC issue is related.  I was just soliciting
feedback for the best way to manage evolving sgc capabilities on
various machines.  In sum, one needs a working mprotect or equivalent,
together with a fault address recovery mechanism.  Redoing the
per-machine header files, rebuilding a new gcl version and then all
apps on top, does not seem very efficient.

Take care,

Matt Kaufmann <address@hidden> writes:

> Hi --
>
> Since you've CCed me on this email, I wonder: Are you suggesting that
> this could be responsible for the control-c bug I reported this
> morning?
>
> Thanks --
> -- Matt
>    Cc: "GCL Development" <address@hidden>,
>          Matt Kaufmann <address@hidden>
>    From: Camm Maguire <address@hidden>
>    Date: Fri, 20 Feb 2009 14:17:41 -0500
>    X-SpamAssassin-Status: No, hits=-2.6 required=5.0
>    X-UTCS-Spam-Status: No, hits=-272 required=165
>
>    Greetings!  GCL has a runtime check for SGC functionality.  This is
>    because it can vary from kernel to kernel and machine to machine,
>    though it is not supposed to.  For example, hppa routinely disables
>    the SGC garbage collecting routine when building applications that use
>    it, notably ACL2.
>
>    I've just confirmed that current Debian sid sparc has an unreliable
>    mprotect at high addresses only, crashing the acl2 build.  Apart from
>    filing a bug, is the best approach to expand the runtime check as
>    follows: 
>
>    
> =============================================================================
>    static int
>    memprotect_test_int(char *b1,unsigned long n) {
>
>      char b2[PAGESIZE];
>      struct sigaction sa,sao,saob;
>
>      if (memprotect_result!=memprotect_none)
>        return memprotect_result!=memprotect_success;
>      if (atexit(memprotect_print)) {
>        fprintf(stderr,"Cannot setup memprotect_print on exit\n");
>        exit(-1);
>      }
>
>      memset(b1,32,n);
>      memset(b2,0,sizeof(b2));
>      memprotect_test_address=(void *)(((unsigned long)b1+PAGESIZE-1) & 
> ~(PAGESIZE-1));
>      if (mprotect(memprotect_test_address,PAGESIZE,PROT_READ_EXEC)) {
>        memprotect_result=memprotect_cannot_protect;
>        return -1;
>      }
>      sa.sa_sigaction=(void *)memprotect_handler_test;
>      sa.sa_flags=MPROTECT_ACTION_FLAGS;
>      if (sigaction(SIGSEGV,&sa,&sao)) {
>        memprotect_result=memprotect_sigaction;
>        return -1;
>      }
>      if (sigaction(SIGBUS,&sa,&saob)) {
>        sigaction(SIGSEGV,&sao,NULL);
>        memprotect_result=memprotect_sigaction;
>        return -1;
>      }
>      memprotect_result=memprotect_bad_return;
>      memset(memprotect_test_address,0,PAGESIZE);
>      if (memprotect_result==memprotect_bad_return)
>        memprotect_result=memprotect_no_signal;
>      if (memprotect_result!=memprotect_none) {
>        sigaction(SIGSEGV,&sao,NULL);
>        sigaction(SIGBUS,&saob,NULL);
>        return -1;
>      }
>      if (memcmp(memprotect_test_address,b2,PAGESIZE)) {
>        memprotect_result=memprotect_no_restart;
>        sigaction(SIGSEGV,&sao,NULL);
>        sigaction(SIGBUS,&saob,NULL);
>        return -1;
>      }
>      memprotect_result=memprotect_success;
>      sigaction(SIGSEGV,&sao,NULL);
>      sigaction(SIGBUS,&saob,NULL);
>      return 0;
>
>    }
>
>    static int
>    memprotect_test(void) {
>
>      char b1[2*PAGESIZE],j;
>
>      if ((j=memprotect_test_int(b1,sizeof(b1))))
>        return j;
>
>      if ((unsigned long)(rb_start-heap_end)<2*PAGESIZE)
>        fprintf(stderr,"Warning: not checking SGC at heap end\n");
>      else {
>        memprotect_result=memprotect_none;
>        memprotect_handler_invocations=0;
>        if ((j=memprotect_test_int(heap_end,2*PAGESIZE)))
>        return j;
>      }
>
>      /*SPARC has trouble with mprotect at high addresses*/
>      if ((unsigned long)(core_end-rb_pointer)<2*PAGESIZE) {
>        fprintf(stderr,"Warning: not checking SGC at rb_pointer\n");
>        return 0;
>      }
>      memprotect_result=memprotect_none;
>      memprotect_handler_invocations=0;
>      return memprotect_test_int(rb_pointer,2*PAGESIZE);
>
>    }
>    
> =============================================================================
>
>    The alternative of course is to remove the ability in the
>    sparc-linux.h file, which then needs reupdating once the problem is
>    fixed.  
>
>
>    Take care,
>    -- 
>    Camm Maguire                                           address@hidden
>    ==========================================================================
>    "The earth is but one country, and mankind its citizens."  --  Baha'u'llah
>
>
>
>
>

-- 
Camm Maguire                                        address@hidden
==========================================================================
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah