Commit 96c64806 authored Apr 25, 2020 by Josh Poimboeuf Committed by Ingo Molnar Apr 25, 2020

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: 8c1f7558 ("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

parent 1fb14363

arch/x86/entry/entry_64.S

+2 −3

Original line number	Diff line number	Diff line
		@@ -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.

Admin message