arm/lib/backtrace-clang.S

13 /* fp is 0 or stack frame */
15 #define frame	r4
34  * We can treat the current frame's lr as the saved pc and the preceding
35  * frame's lr as the current frame's lr, but we can't trace the most recent
36  * call.  Inserting a false stack frame allows us to reference the function
45  * Unfortunately due to the stack frame layout we can't dump r0 - r3, but these
48  * Stack frame layout:
51  * 	frame=> saved fp
54  * 		<top of stack frame>
69  * The frame for c_backtrace has pointers to the code of dump_stack. This is
70  * why the frame of c_backtrace is used to for the pc calculation of
71  * dump_stack. This is why we must move back a frame to print dump_stack.
73  * The stored locals for dump_stack are in dump_stack's frame. This means that
74  * to fully print dump_stack's frame we need both the frame for dump_stack (for
75  * locals) and the frame that was called by dump_stack (for pc).
79  * stack frame.
86  * c_backtrace frame           dump_stack:
92  * dump_stack frame   |        ...
101 		movs	frame, r0		@ if frame pointer is zero
109  * Switches the current frame to be the frame for dump_stack.
111 		add	frame, sp, #24		@ switch to false frame
112 for_each_frame:	tst	frame, mask		@ Check for address exceptions
116  * sv_fp is the stack frame with the locals for the current considered
119  * sv_pc is the saved lr frame the frame above. This is a pointer to a code
124 1001:		ldr	sv_pc, [frame, #4]	@ get saved 'pc'
125 1002:		ldr	sv_fp, [frame, #0]	@ get saved fp
127 		teq	sv_fp, mask		@ make sure next frame exists
145 1003:		ldr	sv_lr, [sv_fp, #4]	@ get saved lr from next frame
170 		mov	r2, frame
181  * continue as if there had been no registers stored in this frame.
186 		ldr	r0, [frame]		@ locals are stored in
187 						@ the preceding frame
193  * If we are out of frames or if the next frame is invalid.
198 		cmp	sv_fp, frame		@ next frame must be
199 		mov	frame, sv_fp		@ above the current frame
203 		@ frame is below the previous frame, accept it as long as it
212 		mov	r2, frame
225 .Lbad:		.asciz	"%sBacktrace aborted due to bad frame pointer <%p>\n"