How to get a stack trace in RTEMS

[Sebastian Huber]

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);
   }
}

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