Need help finding the cause of an ARM4 Exception

Wed Aug 12 20:27:59 UTC 2020

Hi,

Can someone please help me figure out why I am getting
the _ARMV4_Exception_data_abort_default?

I have attached the gdb script (Provided by Mr. Huber) that I used with
this email. I have also printed the commands I have used to run gdb and
qemu.

I have provided my view on this exception and the link to PR with my
changes at the end.

qemu executed with the command:
--------------------------------------------------------------------------------------------------------------------------
 ./qemu-system-arm -net none -nographic -M realview-pbx-a9 -m 256M -kernel
~/quick-start/build/b3-realview/arm-rtems5/c/realview_pbx_a9_qemu/testsuites/smptests/smpstrongapa01.exe
-smp 3 -S -s

--------------------------------------------------------------------------------------------------------------------------

GDB commands used:
--------------------------------------------------------------------------------------------------------------------------

 ~/quick-start/rtems/5/bin$ ./arm-rtems5-gdb --command=arm.gdb
~/quick-start/build/b3-realview/arm-rtems5/c/realview_pbx_a9_qemu/testsuites/smptests/smpstrongapa01.exe
.
.
.
Loading section .fini_array, size 0x4 lma 0x121184
Loading section .rtemsroset, size 0x74 lma 0x121188
Loading section .data, size 0x530 lma 0x200000
Start address 0x00100040, load size 136967
Transfer rate: 26751 KB/sec, 1778 bytes/write.
(gdb) continue
Continuing.

Thread 1 hit Breakpoint 2, _ARMV4_Exception_data_abort_default () at
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/cpu/arm/armv4-exception-default.S:70
70 sub sp, #MORE_CONTEXT_SIZE
(gdb) bt
#0  _ARMV4_Exception_data_abort_default () at
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/cpu/arm/armv4-exception-default.S:70
#1  0x00118c64 in _Scheduler_strong_APA_Get_lowest_scheduled
(context=0x200620 <_Configuration_Scheduler_strong_APA_dflt>,
filter_base=0x201910 <_RTEMS_tasks_Objects+600>) at
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/src/schedulerstrongapa.c:318
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(gdb) reset
Loading section .start, size 0x8e0 lma 0x100000
Loading section .text, size 0x1f00c lma 0x100900
Loading section .init, size 0xc lma 0x11f90c
Loading section .fini, size 0xc lma 0x11f918
Loading section .rodata, size 0x184b lma 0x11f928
Loading section .ARM.exidx, size 0x8 lma 0x121174
Loading section .eh_frame, size 0x4 lma 0x12117c
Loading section .init_array, size 0x4 lma 0x121180
Loading section .fini_array, size 0x4 lma 0x121184
Loading section .rtemsroset, size 0x74 lma 0x121188
Loading section .data, size 0x530 lma 0x200000
Start address 0x00100040, load size 136967
Transfer rate: 8359 KB/sec, 1778 bytes/write.
(gdb) b _Scheduler_strong_APA_Get_lowest_scheduled
Breakpoint 7 at 0x118bee: file
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/src/schedulerstrongapa.c,
line 287.
(gdb) continue
Continuing.

Thread 1 hit Breakpoint 7, _Scheduler_strong_APA_Get_lowest_scheduled
(context=0x200620 <_Configuration_Scheduler_strong_APA_dflt>,
filter_base=0x201910 <_RTEMS_tasks_Objects+600>) at
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/src/schedulerstrongapa.c:287
287  front = 0;
(gdb) ni
0x00118bf0 287  front = 0;
(gdb)
289  rear = -1;
(gdb)
0x00118bf6 289  rear = -1;
(gdb)
291  self = _Scheduler_strong_APA_Get_self( context );
(gdb)
0x00118bfa 291  self = _Scheduler_strong_APA_Get_self( context );
(gdb)
0x00118bfe 291  self = _Scheduler_strong_APA_Get_self( context );
(gdb)
293  visited = self->visited->visited;
(gdb)
0x00118c02 293  visited = self->visited->visited;
(gdb)
0x00118c04 293  visited = self->visited->visited;
(gdb)
294  queue = self->queue->Cpu;
(gdb)
0x00118c08 294  queue = self->queue->Cpu;
(gdb)
0x00118c0a 294  queue = self->queue->Cpu;
(gdb)
295  caller = self->caller->caller;
(gdb)
0x00118c0e 295  caller = self->caller->caller;
(gdb)
0x00118c10 295  caller = self->caller->caller;
(gdb)
297  filter_priority = _Scheduler_Node_get_priority( filter_base );
(gdb)
0x00118c14 297  filter_priority = _Scheduler_Node_get_priority( filter_base
);
(gdb)
0x00118c18 297  filter_priority = _Scheduler_Node_get_priority( filter_base
);
(gdb)
298  filter_priority = SCHEDULER_PRIORITY_PURIFY( filter_priority );
(gdb)
0x00118c20 298  filter_priority = SCHEDULER_PRIORITY_PURIFY(
filter_priority );
(gdb)
0x00118c24 298  filter_priority = SCHEDULER_PRIORITY_PURIFY(
filter_priority );
(gdb)
0x00118c28 298  filter_priority = SCHEDULER_PRIORITY_PURIFY(
filter_priority );
(gdb)
0x00118c2c 298  filter_priority = SCHEDULER_PRIORITY_PURIFY(
filter_priority );
(gdb)
0x00118c30 298  filter_priority = SCHEDULER_PRIORITY_PURIFY(
filter_priority );
(gdb)
300  ret = NULL; //To remove compiler warning.
(gdb)
0x00118c36 300  ret = NULL; //To remove compiler warning.
(gdb)
304  filter_node = _Scheduler_strong_APA_Node_downcast( filter_base );
(gdb)
0x00118c3a 304  filter_node = _Scheduler_strong_APA_Node_downcast(
filter_base );
(gdb)
0x00118c3e 304  filter_node = _Scheduler_strong_APA_Node_downcast(
filter_base );
(gdb)
306  max_priority_num = 0;//Max (Lowest) priority encountered so far.
(gdb)
0x00118c44 306  max_priority_num = 0;//Max (Lowest) priority encountered so
far.
(gdb)
312  cpu_max = _SMP_Get_processor_maximum();
(gdb)
0x00118c4c 312  cpu_max = _SMP_Get_processor_maximum();
(gdb)
314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118c50 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118c52 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118cb2 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118cb4 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118cb6 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
0x00118cb8 314  for ( cpu_index = 0 ; cpu_index < cpu_max ; ++cpu_index ) {
(gdb)
315    visited[ cpu_index ] = false;
(gdb)
0x00118c56 315    visited[ cpu_index ] = false;
(gdb)
0x00118c58 315    visited[ cpu_index ] = false;
(gdb)
0x00118c5a 315    visited[ cpu_index ] = false;
(gdb)
0x00118c5c 315    visited[ cpu_index ] = false;
(gdb)

Thread 1 hit Breakpoint 2, _ARMV4_Exception_data_abort_default () at
/home/richi/quick-start/src/rtems/c/src/../../cpukit/score/cpu/arm/armv4-exception-default.S:70
70 sub sp, #MORE_CONTEXT_SIZE
(gdb)
71 stmdb sp!, {r0-r12}
(gdb)
--------------------------------------------------------------------------------------------------------------------------

The exception occurs just after the visited array gets (or tries to get)
initialized.
I believe this could be because :

1) I might not have defined the variable properly here
<https://github.com/richidubey/rtems/pull/7/files#diff-9a1c6e240a276a856e99c45d87f1a02f>
between lines 260 to 262 . I do not understand how this configuration
definition works in this case, i.e. for SCHEDULER_STRONG_APA_CONTEXT_NAME(
name  ) or for #define RTEMS_SCHEDULER_STRONG_APA( name, prio_count ). I
would appreciate it if someone could explain to me how this works.

2) Of this <https://github.com/richidubey/rtems/pull/4/files#r461843786>
comment
by Dr. Bloom. which I still don't know how to address. Someone, please help
me out with this as well.

Please find the Pull Request at: https://github.com/richidubey/rtems/pull/7

Thanks,
Richi.
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