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x86/xen: Mark cpu_bringup_and_idle() as dead_end_function
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commit 9af9dcf upstream.

The asm_cpu_bringup_and_idle() function is required to push the return
value on the stack in order to make ORC happy, but the only reason
objtool doesn't complain is because of a happy accident.

The thing is that asm_cpu_bringup_and_idle() doesn't return, so
validate_branch() never terminates and falls through to the next
function, which in the normal case is the hypercall_page. And that, as
it happens, is 4095 NOPs and a RET.

Make asm_cpu_bringup_and_idle() terminate on it's own, by making the
function it calls as a dead-end. This way we no longer rely on what
code happens to come after.

Fixes: c3881eb ("x86/xen: Make the secondary CPU idle tasks reliable")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lore.kernel.org/r/20210624095147.693801717@infradead.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Peter Zijlstra authored and Greg Kroah-Hartman committed May 25, 2022
1 parent a12884f commit 10a221e
Showing 1 changed file with 1 addition and 0 deletions.
1 change: 1 addition & 0 deletions tools/objtool/check.c
Original file line number Diff line number Diff line change
@@ -144,6 +144,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
"usercopy_abort",
"machine_real_restart",
"rewind_stack_do_exit",
"cpu_bringup_and_idle",
};

if (!func)

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