On 4 Oct 2012, at 1:05 PM, Larry Baker wrote:
> I am still puzzled, though, why uClinux is silent when a program is aborted
> when it receives an unhandled fatal signal. Mainline Linux (really the
> shell?) prints out a message like
>
>> [root@atompc sdk]# ./SIGILL
>> Illegal instruction
>
> (SIGILL.c is the example program from http://en.wikipedia.org/wiki/SIGILL.)
> After a reboot of uClinux, I get nothing
>
>> / # SIGILL
>
> I have to enable print-fatal-signals as before to see anything:
>
>> / # echo 1 >/proc/sys/kernel/print-fatal-signals
>> / # SIGILL
>> SIGILL/79: potentially unexpected fatal signal 4.
>>
>>
>> Format 04 Vector: 002c PC: 4052e544 Status: 0000 Not tainted
>> ORIG_D0: ffffffff D0: 4052e544 A2: 4052ff60 A1: 4052e4ec
>> A0: 4052e544 D5: 4052e524 D4: 00000000
>> D3: 00000000 D2: 00000001 D1: 0000002f
>> USP: 4052ff04
>
> Is this a uClinux thing? Or, a BusyBox (my uClinux shell) thing?
I'll answer my own question.
It is the shell that prints out the "Illegal instruction" message. I found the
code in bash that does that and added it to the BusyBox hush shell. The SDK I
use has a rather old BusyBox, 1.13.3. The hush shell is in
busybox-1.13.3/shell/hush.c. checkjobs() waits for all child processes --
there is no distinction made between job control jobs and non-job control jobs
like there is in bash. There is already code there that can be (hand) enabled
to be verbose about what happens to a job. Enabling that also makes hush very
chatty. So, I added an #else clause for the #if DEBUG_JOBS conditional code in
checkjobs() to mimic bash's behavior. Here's the patch for busybox-1.13.3:
--- busybox-1.13.3/shell/hush.c
+++ busybox-1.13.3-patched/shell/hush.c
@@ -1720,2 +1720,13 @@
childpid, WEXITSTATUS(status));
> +#else
> + if ((WIFSTOPPED (status) == 0) && WIFSIGNALED (status)) {
> + int sig = WTERMSIG (status);
> + if ((sig != SIGINT) && (sig != SIGPIPE)) {
> + char *s = strsignal (sig);
> + if ( s != NULL )
> + fprintf (stderr, "%s\n", s);
> + else
> + fprintf (stderr, "Unknown signal:
> %d\n", sig);
> + }
> + }
> #endif
With this patched hush, I get what I am used to seeing:
> / # trap
> Illegal instruction
> / # SIGILL
> Illegal instruction
Now I can go back and find out where the applications I use are failing. I
suspect stack overflows, which my implementation of gcc
-stack-check-symbol=__stack_start for non-68020 (e.g., ColdFire) processors can
catch now.
Larry Baker
US Geological Survey
650-329-5608
ba...@usgs.gov
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