x86/unwind/orc: Unwind ftrace trampolines with correct ORC entry

When meeting ftrace trampolines in ORC unwinding, unwinder uses address
of ftrace_{regs_}call address to find the ORC entry, which gets next frame at
sp+176.

If there is an IRQ hitting at sub $0xa8,%rsp, the next frame should be
sp+8 instead of 176. It makes unwinder skip correct frame and throw
warnings such as "wrong direction" or "can't access registers", etc,
depending on the content of the incorrect frame address.

By adding the base address ftrace_{regs_}caller with the offset
*ip - ops->trampoline*, we can get the correct address to find the ORC entry.

Also change "caller" to "tramp_addr" to make variable name conform to
its content.

[ mingo: Clarified the changelog a bit. ]

Fixes: 6be7fa3 ("ftrace, orc, x86: Handle ftrace dynamically allocated trampolines")
Signed-off-by: Chen Zhongjin <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Reviewed-by: Steven Rostedt (Google) <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: Chen Zhongjin

arch/x86/kernel/unwind_orc.c

@@ -93,22 +93,27 @@ static struct orc_entry *orc_find(unsigned long ip);
 static struct orc_entry *orc_ftrace_find(unsigned long ip)
 {
 	struct ftrace_ops *ops;
-	unsigned long caller;
+	unsigned long tramp_addr, offset;
 
 	ops = ftrace_ops_trampoline(ip);
 	if (!ops)
 		return NULL;
 
+	/* Set tramp_addr to the start of the code copied by the trampoline */
 	if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
-		caller = (unsigned long)ftrace_regs_call;
+		tramp_addr = (unsigned long)ftrace_regs_caller;
 	else
-		caller = (unsigned long)ftrace_call;
+		tramp_addr = (unsigned long)ftrace_caller;
+
+	/* Now place tramp_addr to the location within the trampoline ip is at */
+	offset = ip - ops->trampoline;
+	tramp_addr += offset;
 
 	/* Prevent unlikely recursion */
-	if (ip == caller)
+	if (ip == tramp_addr)
 		return NULL;
 
-	return orc_find(caller);
+	return orc_find(tramp_addr);
 }
 #else
 static struct orc_entry *orc_ftrace_find(unsigned long ip)