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objtool: Introduce HINT_RET_OFFSET

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Normally objtool ensures a function keeps the stack layout invariant.
But there is a useful exception, it is possible to stuff the return
stack in order to 'inject' a 'call':

	push $fun
	ret

In this case the invariant mentioned above is violated.

Add an objtool HINT to annotate this and allow a function exit with a
modified stack frame.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200416115118.690601403@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2020-04-01 16:38:19 +02:00
committed by Ingo Molnar
parent b746046238
commit e25eea89bb
5 changed files with 31 additions and 9 deletions
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10
arch/x86/include/asm/unwind_hints.h
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@@ -94,6 +94,16 @@
UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
.endm
/*
* RET_OFFSET: Used on instructions that terminate a function; mostly RETURN
* and sibling calls. On these, sp_offset denotes the expected offset from
* initial_func_cfi.
*/
.macro UNWIND_HINT_RET_OFFSET sp_offset=8
UNWIND_HINT type=UNWIND_HINT_TYPE_RET_OFFSET sp_offset=\sp_offset
.endm
#else /* !__ASSEMBLY__ */
#define UNWIND_HINT(sp_reg, sp_offset, type, end) \