Revert "x86/unwind: Handle NULL pointer calls better in frame unwinder"

This reverts commit c60f18c.
It breaks KABI.

Orabug: 30540100

Signed-off-by: Wengang Wang <[email protected]>
Reviewed-by: John Donnelly <[email protected]>
Signed-off-by: Somasundaram Krishnasamy <[email protected]>

Author: Wengang-oracle

arch/x86/include/asm/unwind.h

@@ -23,12 +23,6 @@ struct unwind_state {
 #elif defined(CONFIG_UNWINDER_FRAME_POINTER)
 	bool got_irq;
 	unsigned long *bp, *orig_sp, ip;
-	/*
-	 * If non-NULL: The current frame is incomplete and doesn't contain a
-	 * valid BP. When looking for the next frame, use this instead of the
-	 * non-existent saved BP.
-	 */
-	unsigned long *next_bp;
 	struct pt_regs *regs;
 #else
 	unsigned long *sp;

arch/x86/kernel/unwind_frame.c

@@ -320,14 +320,10 @@ bool unwind_next_frame(struct unwind_state *state)
 	}
 
 	/* Get the next frame pointer: */
-	if (state->next_bp) {
-		next_bp = state->next_bp;
-		state->next_bp = NULL;
-	} else if (state->regs) {
+	if (state->regs)
 		next_bp = (unsigned long *)state->regs->bp;
-	} else {
+	else
 		next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);
-	}
 
 	/* Move to the next frame if it's safe: */
 	if (!update_stack_state(state, next_bp))
@@ -402,21 +398,6 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 
 	bp = get_frame_pointer(task, regs);
 
-	/*
-	 * If we crash with IP==0, the last successfully executed instruction
-	 * was probably an indirect function call with a NULL function pointer.
-	 * That means that SP points into the middle of an incomplete frame:
-	 * *SP is a return pointer, and *(SP-sizeof(unsigned long)) is where we
-	 * would have written a frame pointer if we hadn't crashed.
-	 * Pretend that the frame is complete and that BP points to it, but save
-	 * the real BP so that we can use it when looking for the next frame.
-	 */
-	if (regs && regs->ip == 0 &&
-	    (unsigned long *)kernel_stack_pointer(regs) >= first_frame) {
-		state->next_bp = bp;
-		bp = ((unsigned long *)kernel_stack_pointer(regs)) - 1;
-	}
-
 	/* Initialize stack info and make sure the frame data is accessible: */
 	get_stack_info(bp, state->task, &state->stack_info,
 		       &state->stack_mask);
@@ -429,7 +410,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	 */
 	while (!unwind_done(state) &&
 	       (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
-			(state->next_bp == NULL && state->bp < first_frame)))
+			state->bp < first_frame))
 		unwind_next_frame(state);
 }
 EXPORT_SYMBOL_GPL(__unwind_start);