How to get a stack trace in RTEMS

[Stanislav Pankevich]

Hi Sebastian,

We had to add -funwind-tables to have this trace() called, and we can now
see the function names as follows. The challenge is that the functions of
the exception handler are printed, not the code that led to the exception.
Now we need to figure out how to switch this code to print our function
names instead.

FUNC NAME: bsp_fatal_extension
FUNC NAME: _User_extensions_Iterate
FUNC NAME: _Terminate
FUNC NAME: _ARM_Exception_default

static _Unwind_Reason_Code trace(_Unwind_Context *ctx, void *arg)
{
    (void)arg;

    const uint32_t func_entry  = _Unwind_GetRegionStart(ctx);

    char          *func_name = "??";
    uint8_t       *canary    = (uint8_t *)(func_entry - 0x4);
    const uint32_t len       = (*((uint32_t *)(func_entry - 0x4))) &
0x00FFFFFF;
    if (*canary == 0xFF)
    {
        func_name = (char *)((uint32_t)canary - len);
        *canary   = '\0';
    }
    printk("FUNC NAME: %s\n", func_name);

    return _URC_NO_REASON;
}

Thanks,
Stanislav Pankevich

On Wed, Jun 26, 2024 at 11:25 AM Sebastian Huber <
sebastian.huber at embedded-brains.de> wrote:

> Hello Stanislav,
>
> On 26.06.24 11:15, Stanislav Pankevich wrote:
> > Dear RTEMS community,
> >
> > My colleague George cannot register to post to this forum, getting 403
> > when subscribing at https://lists.rtems.org/mailman/listinfo/users
> > <https://lists.rtems.org/mailman/listinfo/users>. I am posting this
> > question on his behalf.
> >
> > ---
> >
> > We are currently seeing an RTEMS_FATAL_SOURCE_EXCEPTION right at the
> > start of execution and can debug the program once the exception handler
> > has been reached. From here we can inspect the call stack however we
> > only see the trace that led to the final function call (void
> > bsp_reset(void) while loop) that handles the exception, not the trace
> > that caused the exception. We would like to implement an exception
> > handler that prints the trace that caused the exception to be triggered.
> > Is this something that is already implemented in RTEMS? We have
> > developed an RTEMS port to the Zynq UltraScale+ MPSoC Cortex R5 RPU
> > running in lockstep. Code execution is from the shared DDR4 memory with
> > a 256MB region allocated.
>
> I have some improvements for this BSP in my patch queue. It adds support
> for the split mode for example.
>
> >
> > What we want is to have the actual stack trace to be printed to the
> console.
> >
> > Here is an example of what we have now in GDB:
> >
> > bsp_reset at 0x0017b062
> > (.../rtems/bsps/arm/xilinx-zynqmp-rpu/start/bspreset.c:40)
> > _User_extensions_Iterate at 0x00186854
> > (.../rtems/cpukit/score/src/userextiterate.c:194)
> > _User_extensions_Fatal at 0x00183108
> > (.../rtems/cpukit/include/rtems/score/userextimpl.h:467)
> > _Terminate at 0x00183108 (.../rtems/cpukit/score/src/interr.c:55)
> > rtems_fatal at 0x0018adc2 (.../rtems/cpukit/include/rtems/fatal.h:160)
> > _ARM_Exception_default at 0x0018adc2
> > (.../rtems/cpukit/score/cpu/arm/arm-exception-default.c:37)
> > save_more_context at 0x00186cfc
> > (.../rtems/cpukit/score/cpu/arm/armv4-exception-default.S:176)
> >
> > This is currently what is printed on the serial port:
> >
> > *** FATAL ***
> > fatal source: 9 (RTEMS_FATAL_SOURCE_EXCEPTION)
> >
> > R0   = 0x00000056 R8  = 0x00ac8aec
> > R1   = 0xf000e3a0 R9  = 0x00ac8a5c
> > R2   = 0x00000020 R10 = 0x00000000
> > R3   = 0x00000020 R11 = 0x00000000
> > R4   = 0x00000056 R12 = 0x010e6630
> > R5   = 0x010e67c0 SP  = 0x010e65d4
> > R6   = 0x010e6698 LR  = 0x001854ae
> > R7   = 0x001867f5 PC  = 0x001854ae
> > CPSR = 0x200f01f7 VEC = 0x00000004
> > RTEMS version: 6.0.0.62f15c07482dd953663143554e78b4bf287ccb83
> > RTEMS tools: 12.2.1 20230224 (RTEMS 6, RSB
> > 4c73a76c802588d3864c64ee4dd48a84b953201a, Newlib 17ac400)
>
> Getting stack traces on arm is not that easy since you need a
> description of the stack frames. You can try to use the unwinder from
> libgcc:
>
> static _Unwind_Reason_Code trace(_Unwind_Context *ctx, void *arg)
> {
>    (void)arg;
>    printk("%08" PRIuPTR "\n", (uintptr_t)_Unwind_GetIP(ctx));
>    return _URC_NO_REASON;
> }
>
> static void f(int i);
>
> static void h(int i)
> {
>    f(i + 1);
> }
>
> static void f(int i)
> {
>    if (i > 10) {
>      _Unwind_Backtrace(trace, NULL);
>    } else {
>       h(i + 1);
>    }
> }
>
> --
> embedded brains GmbH & Co. KG
> Herr Sebastian HUBER
> Dornierstr. 4
> 82178 Puchheim
> Germany
> email: sebastian.huber at embedded-brains.de
> phone: +49-89-18 94 741 - 16
> fax:   +49-89-18 94 741 - 08
>
> Registergericht: Amtsgericht München
> Registernummer: HRB 157899
> Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
> Unsere Datenschutzerklärung finden Sie hier:
> https://embedded-brains.de/datenschutzerklaerung/
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/users/attachments/20240626/205bc098/attachment.htm>