microblaze: Add stack unwinder

Implement intelligent backtracing by searching for stack frame creation,
and emitting only return addresses. Use print_hex_dump() to display the
entire binary kernel stack.

Limitation: MMU kernels are not currently able to trace beyond a system trap
(interrupt, syscall, etc.). It is the intent of this patch to provide
infrastructure that can be extended to add this capability later.

Changes from V1:
* Removed checks in find_frame_creation() that prevented location of the frame
  creation instruction in heavily optimized code
* Various formatting/commenting/file location tweaks per review comments
* Dropped Kconfig option to enable STACKTRACE as something logically separate

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 077377a5d0c..7a19d8910e3 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -1127,3 +1127,30 @@ ENTRY(_break)
 
 syscall_table_size=(.-sys_call_table)
 
+type_SYSCALL:
+        .ascii "SYSCALL\0"
+type_IRQ:
+        .ascii "IRQ\0"
+type_IRQ_PREEMPT:
+        .ascii "IRQ (PREEMPTED)\0"
+type_SYSCALL_PREEMPT:
+        .ascii " SYSCALL (PREEMPTED)\0"
+
+        /*
+         * Trap decoding for stack unwinder
+         * Tuples are (start addr, end addr, string)
+         * If return address lies on [start addr, end addr],
+         * unwinder displays 'string'
+         */
+
+        .align 4
+.global microblaze_trap_handlers
+microblaze_trap_handlers:
+        /* Exact matches come first */
+        .word ret_from_trap; .word ret_from_trap   ; .word type_SYSCALL
+        .word ret_from_irq ; .word ret_from_irq    ; .word type_IRQ
+        /* Fuzzy matches go here */
+        .word ret_from_irq ; .word no_intr_resched ; .word type_IRQ_PREEMPT
+        .word ret_from_trap; .word TRAP_return     ; .word type_SYSCALL_PREEMPT
+        /* End of table */
+        .word 0               ; .word 0               ; .word 0