On 27.06.24 10:27, Stanislav Pankevich wrote:
A small further update here to support the discussion further. It turns
out that there is an undocumented function that, in contrast to
_Unwind_Backtrace, allows passing a given stack:
/ In my practice standard _Unwind_Backtrace failed to switch to
pre-signal stack. I've managed to get some before-signal stacks by
calling internal libgcc __gnu_Unwind_Backtrace - it has an extra
argument being "current registry values" - so it operates on given
stack, not on current stack./
https://stackoverflow.com/a/30515756/598057
<https://stackoverflow.com/a/30515756/598057>
The challenge with this is how to access the crashed stack frame, i.e.,
the right context has to be passed to __gnu_Unwind_Backtrace.
|_Unwind_Reason_Code __gnu_Unwind_Backtrace(_Unwind_Trace_Fn trace, void
* trace_argument, phase2_vrs * entry_vrs);||
...
pre_signal_state.core = *reinterpret_cast<const
core_regs*>(&(signal_context->uc_mcontext.arm_r0));
__gnu_Unwind_Backtrace(tracer, &state, &pre_signal_state);|
In this SO example, they are using the signal_context while what we have
in the RTEMS, for example in bsp_fatal_extension() is:
const rtems_exception_frame *exception_frame = (const
rtems_exception_frame *) code;
Could anyone advise on how we access the original crashed stack trace
from the code variable? We confirm that _Unwind_Backtrace can work on
both Zynq UltraScale+ and TMS570. It would be great to get it or
__gnu_Unwind_Backtrace to work with the real user frames.
The rtems_exception_frame is CPU port specific. For arm, we have:
typedef struct {
uint32_t register_r0;
uint32_t register_r1;
uint32_t register_r2;
uint32_t register_r3;
uint32_t register_r4;
uint32_t register_r5;
uint32_t register_r6;
uint32_t register_r7;
uint32_t register_r8;
uint32_t register_r9;
uint32_t register_r10;
uint32_t register_r11;
uint32_t register_r12;
uint32_t register_sp;
void *register_lr;
void *register_pc;
#if defined(ARM_MULTILIB_ARCH_V4)
uint32_t register_cpsr;
Arm_symbolic_exception_name vector;
#elif defined(ARM_MULTILIB_ARCH_V6M) || defined(ARM_MULTILIB_ARCH_V7M)
uint32_t register_xpsr;
uint32_t vector;
#endif
const ARM_VFP_context *vfp_context;
uint32_t reserved_for_stack_alignment;
} CPU_Exception_frame;
This is basically the full register view of the interrupted context.
For arm, the register_pc needs adjustments to get the real PC.
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