[LCP]SIGBUS question

[Bill Rausch]

You're using a switch statement on the pid?  Looking for -1, 0, default?

Which process is getting the signal, the parent or the child?  Or is fork()
failing and you're not checking for the -1?

Bill


At 11:44 PM +0200 4/19/02, Joachim Bauernberger wrote:
>Ok, After spending the evening with my best friend gdb I managed to
>pinpoint the location of the problem but have still no glue on what
>might be the cause :-((
>
>As soon as myfunc() calls fork, the process looses all it's information
>on previous stackframes. At this point I haven't even called exec()
>yet.
>
>Look here, those are the frames before calling fork (sorry if the lines
>wrap):
>
>(gdb) bt
>#0  local_inject (data=0xbfffa73c, rcpt=0x80d36b0
>"bj at bjdev.devel.gmx.net") at mda.c:198
>#1  0x8060398 in mknotify (what=665, who=2) at report.c:432
>#2  0x80504d9 in av_scan (entry=0xbfffb86c
>"/var/mxscan/scan//jbauernberger at gmx-ag.de-2002419232533-32132/1-base64-ZqKkai")
>at av_scan.c:50
>#3  0x804a5cc in b64decode (b64str=0x80d7de4, tnef=0, checksum=0x0) at
>b64decode.c:92
>#4  0x8050061 in mimeget (
>     startpos=0x8071382 "\n\n\n", '-' <repeats 14 times>,
>"Boundary-00=_XXOTHOLISLOHA8DOE9Z7\nContent-Type: text/plain;\n 
>charset=\"us-ascii\"\nContent-Transfer-Encoding: 8bit\nSubject:
>\n\n\n-- \nPGP Public
>Key:\nhttp://www.mXscan.org/pgp/public.html\n"...) at mimeget.c:292
>#5  0x804dfb3 in header (mref=0xbffffb1c) at header.c:729
>#6  0x8053b7c in main (argc=18, argv=0xbffffba4) at main.c:772
>#7  0x40119baf in __libc_start_main () from /lib/libc.so.6
>
>Now at line 210:
>(gdb) n
>210         switch ((pid = fork ())) {
>
>Immediately after fork the frame history is gone.
>(gdb) bt
>#0  local_inject (data=0xbfffa73c, rcpt=0x80d36b0
>"bj at bjdev.devel.gmx.net") at mda.c:210
>(gdb)
>
>That's it. The process then segfaults on return:
>(gdb) cont
>Continuing.
>Program received signal SIGSEGV, Segmentation fault.
>
>0x806059d in mknotify (what=Cannot access memory at address 0xfffffffe
>) at report.c:432
>432                     rc = local_inject(&notification, rcpt);
>
>
>Thanks,
>Joachim
>
>On Friday 19 April 2002 14:11, Joachim Bauernberger wrote:
>>  Hi,
>>  Can someone please take the time to explain to me what can cause a
>>  SIGBUS to be raised by a program (other than mmap) under Linux?
>>  I have been "googling" for answers and found that it's cause seems to
>be
>>  architecture dependent?
>>  (I've been able to catch it by setting up a signal handler but this
>>  doesn't give much information other than it was indeed a SIGBUS that
>>  crashed the program)
>>
>>  Also raise()ing a SIGSTOP and then attaching to the process with gdb
>>  shows me it's a SIGBUS but the information gdb gives me is not very
>>  descriptive about why the problem occurs. It seems that on return from
>>  myfunc() (which calls fork/exec and writes and reads with pipes
>to/from
>>  the forked child) the programs memory gets corrupted.
>>
>>  I started getting the problem after moving some code into myfunc() .
>>  Now when the myfunc() returns the SIGBUS
>>  results. Looking at gdb's output:
>>
>>  Program received signal SIGBUS, Bus error.
>>  mknotify (what=Cannot access memory at address 0xffffef36.
>>  ) at report.c:450
>>  450             if (recipient) free(recipient);
>>
>>  mknotify() is the function calling myfunc()  and "what" is an int
>passed
>>  to it as it's first parameter.
>>
>>  This confuses me since I am not calling mknotify() any more upon
>return
>>  >from myfunc() (before the sigbus).
>>  Am I right to say that something in myfunc() corrupts the stack of my
>>  program so badly that upon it's return the program does not know
>>  anymore where to carry on?
>>
>>  The system I have the problem is a linux libc5 box (i386) Kernel
>2.0.38
>>  (don't tell me to upgrade please :-))
>>
>>  Thanks & Regards,
>>  Joachim
>>
>>  --
>>  PGP Public Key:
>>  http://www.mXscan.org/pgp/public.html
>>
>>
>>  _______________________________________________
>>  This is the Linux C Programming List
>>  :  http://lists.linux.org.au/listinfo/linuxcprogramming List
>  >
>>
>
>--
>PGP Public Key:
>http://www.mXscan.org/pgp/public.html
>
>
>_______________________________________________
>This is the Linux C Programming List
>:  http://lists.linux.org.au/listinfo/linuxcprogramming List


-- 
Bill Rausch, Software Development, UNIX, Mac, Windows
Numerical Applications, Richland, WA  509-943-0861