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Subject[tip: objtool/core] objtool: Fix stack-swizzle for FRAME_POINTER=y
The following commit has been merged into the objtool/core branch of tip:

Commit-ID: 23e34c5988088b8bb4c55905973ca76114cb33ee
Gitweb: https://git.kernel.org/tip/23e34c5988088b8bb4c55905973ca76114cb33ee
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 18 Feb 2021 17:14:10 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Mon, 22 Feb 2021 12:05:18 +01:00

objtool: Fix stack-swizzle for FRAME_POINTER=y

When objtool encounters the stack-swizzle:

mov %rsp, (%[tos])
mov %[tos], %rsp
...
pop %rsp

Inside a FRAME_POINTER=y build, things go a little screwy because
clearly we're not adjusting the cfa->base. This then results in the
pop %rsp not being detected as a restore of cfa->base so it will turn
into a regular POP and offset the stack, resulting in:

kernel/softirq.o: warning: objtool: do_softirq()+0xdb: return with modified stack frame

Therefore, have "mov %[tos], %rsp" act like a PUSH (it sorta is
anyway) to balance the things out. We're not too concerned with the
actual stack_size for frame-pointer builds, since we don't generate
ORC data for them anyway.

Fixes: aafeb14e9da2 ("objtool: Support stack-swizzle")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/YC6UC+rc9KKmQrkd@hirez.programming.kicks-ass.net
---
tools/objtool/check.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 62cd211..d7f1496 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1983,6 +1983,20 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
}
}

+ else if (op->dest.reg == CFI_SP &&
+ cfi->vals[op->src.reg].base == CFI_SP_INDIRECT &&
+ cfi->vals[op->src.reg].offset == cfa->offset) {
+
+ /*
+ * The same stack swizzle case 2) as above. But
+ * because we can't change cfa->base, case 3)
+ * will become a regular POP. Pretend we're a
+ * PUSH so things don't go unbalanced.
+ */
+ cfi->stack_size += 8;
+ }
+
+
break;

case OP_SRC_ADD:
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