On Wed, Feb 10, 2021 at 08:01:23PM -0000, tip-bot2 for Peter Zijlstra wrote:
> objtool: Support stack-swizzle
---
Subject: objtool: Fix stack-swizzle for FRAME_POINTER=y
From: Peter Zijlstra <pet...@infradead.org>
Date: Thu Feb 18 17:14:10 CET 2021
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 <l...@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
tools/objtool/check.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1996,6 +1996,20 @@ static int update_cfi_state(struct instr
}
}
+ 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:
