[tip: x86/urgent] x86/entry/64: Fix unwind hints in __switch_to_asm()

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     96c64806b4bf35f5edb465cafa6cec490e424a30
Gitweb:        https://git.kernel.org/tip/96c64806b4bf35f5edb465cafa6cec490e424a30
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Sat, 25 Apr 2020 05:03:03 -05:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sat, 25 Apr 2020 12:22:28 +02:00

x86/entry/64: Fix unwind hints in __switch_to_asm()

UNWIND_HINT_FUNC has some limitations: specifically, it doesn't reset
all the registers to undefined.  This causes objtool to get confused
about the RBP push in __switch_to_asm(), resulting in bad ORC data.

While __switch_to_asm() does do some stack magic, it's otherwise a
normal callable-from-C function, so just annotate it as a function,
which makes objtool happy and allows it to produces the correct hints
automatically.

Fixes: 8c1f75587a18 ("x86/entry/64: Add unwind hint annotations")
Reviewed-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Dave Jones <dsj@xxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Link: https://lore.kernel.org/r/03d0411920d10f7418f2e909210d8e9a3b2ab081.1587808742.git.jpoimboe@xxxxxxxxxx
---
 arch/x86/entry/entry_64.S | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 6b0d679..34a5889 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -279,8 +279,7 @@ SYM_CODE_END(entry_SYSCALL_64)
  * %rdi: prev task
  * %rsi: next task
  */
-SYM_CODE_START(__switch_to_asm)
-	UNWIND_HINT_FUNC
+SYM_FUNC_START(__switch_to_asm)
 	/*
 	 * Save callee-saved registers
 	 * This must match the order in inactive_task_frame
@@ -321,7 +320,7 @@ SYM_CODE_START(__switch_to_asm)
 	popq	%rbp
 
 	jmp	__switch_to
-SYM_CODE_END(__switch_to_asm)
+SYM_FUNC_END(__switch_to_asm)
 
 /*
  * A newly forked process directly context switches into this address.