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Subject[tip: x86/urgent] x86/entry/64: Fix unwind hints in __switch_to_asm()
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@redhat.com>
AuthorDate: Sat, 25 Apr 2020 05:03:03 -05:00
Committer: Ingo Molnar <mingo@kernel.org>
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@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Jones <dsj@fb.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: https://lore.kernel.org/r/03d0411920d10f7418f2e909210d8e9a3b2ab081.1587808742.git.jpoimboe@redhat.com
---
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.
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