About HEAP error

[Joel Sherrill]

On Wed, Mar 3, 2021 at 9:50 AM Gedare Bloom <gedare at rtems.org> wrote:

> On Wed, Mar 3, 2021 at 12:08 AM Richi Dubey <richidubey at gmail.com> wrote:
> >
> > What's the element written after the free? I set a watch at the exact
> block location, but it doesn't work:
> >
> > Hardware watchpoint 7: *0x202ba8
> > (gdb) watch *0x206fec
> > Hardware watchpoint 8: *0x206fec
> That's just the first byte in the block. If you can figure out which
> bytes/words in the block get accessed that would help you.
>

What about watch *(unsigned int)*  0x202ba8?

Won't that look at more bytes?

In case you do need to look at more bytes in the fence...
breaking at _Terminate and doing a back trace will give
you the exact line the error is raised from. You can then set a
breakpoint at that on the next line and look at local variables.
The corruption may be in the fence somewhere beyond the
first 32-bits.

Sometimes it is easy to binary search for an issue like this
on a simulator. But with a watchpoint, you should be able to
determine the precise word which is corrupted in the fence
and break on that write.

--joel

>
> > (gdb) c
> > Continuing.
> >
> > Thread 1 hit Breakpoint 6, Init (argument=2107944) at
> /home/richi/quick-start/LatestStrong/src/rtems/c/src/../../testsuites/sptests/sp02/init.c:26
> > 26  TEST_BEGIN();
> > (gdb)
> > Continuing.
> >
> > Thread 1 hit Breakpoint 5, _Terminate
> (the_source=RTEMS_FATAL_SOURCE_HEAP, the_error=2125180) at
> /home/richi/quick-start/LatestStrong/src/rtems/c/src/../../cpukit/score/src/interr.c:38
> > 38  _User_extensions_Fatal( the_source, the_error );
> > (gdb)
> > Continuing.
> >
> > Thread 1 hit Breakpoint 4, bsp_reset () at
> /home/richi/quick-start/LatestStrong/src/rtems/c/src/lib/libbsp/arm/realview-pbx-a9/../../../../../../bsps/arm/realview-pbx-a9/start/bspreset.c:19
> > 19  volatile uint32_t *sys_lock = (volatile uint32_t *) 0x10000020;
> > (gdb)
> >
> > On Wed, Mar 3, 2021 at 12:31 PM Sebastian Huber <
> sebastian.huber at embedded-brains.de> wrote:
> >>
> >> On 02/03/2021 05:44, Richi Dubey wrote:
> >>
> >> >
> >> > (gdb) p *(Heap_Error_context*)(0x00206d7c)
> >> > $5 = {
> >> >   heap = 0x202ba8 <_Workspace_Area>,
> >> >   block = 0x206fec,
> >> >   reason = HEAP_ERROR_FREE_PATTERN
> >> > }
> >>
> >> If it is always the same address, then you can set a watch point to an
> >> element which is written after the free to catch the function which
> >> writes into this area.
> >>
> >> --
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