[GDB stub]first version

components/gdb/libcpu/cortexm/gdb_gcc.S

@@ -0,0 +1,27 @@
+.cpu cortex-m4
+.syntax unified
+.thumb
+.text
+
+.global DebugMon_Handler
+.type DebugMon_Handler, %function
+DebugMon_Handler:
+    mrs     r0,psp                  ;// Get process stack
+    sub     r1,r0,#(4*13)           ;// Make space for saved state
+    msr     psp,r1                  ;// Ensure PSP is up to date
+
+    mov     r12,r0                  ;// R12 = stack
+    mov     r1,#1                   ;// R1 = exception state type
+    mrs     r2,ipsr                 ;// R2 = vector number
+    mrs     r3,basepri              ;// R3 = basepri
+    stmfd   r0!,{r1-r12,lr}         ;// Push type, vector, basepri, r4-11 
+
+    mov     r4,r0                   ;// R4 = saved state pointer
+    bl      rt_hw_debugmon_exception
+
+    mov     r0,r4                   ;// R4 = saved state pointer
+    ldmfd   r0!,{r1-r12,lr}         ;// Pop type, vec, basepri, registers and LR
+    msr     psp,r0                  ;// Restore PSP
+    msr     basepri,r3              ;// Restore basepri
+
+    bx      lr                      ;// Return