linux-kernel - Re: [PATCH 3/3] objtool: check: Make SP memory operation match PUSH/POP semantics

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Date:   Fri, 18 Sep 2020 16:43:18 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Julien Thierry <jthierry@...hat.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, mbenes@...e.cz,
        raphael.gault@....com, benh@...nel.crashing.org
Subject: Re: [PATCH 3/3] objtool: check: Make SP memory operation match
 PUSH/POP semantics

On Tue, Sep 15, 2020 at 09:12:04AM +0100, Julien Thierry wrote:
> Architectures without PUSH/POP instructions will always access the stack
> though memory operations (SRC/DEST_INDIRECT). Make those operations have
> the same effect on the CFA as PUSH/POP, with no stack pointer
> modification.
> 
> Signed-off-by: Julien Thierry <jthierry@...hat.com>
> ---
>  tools/objtool/check.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index f45991c2db41..7ff87fa3caec 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2005,6 +2005,13 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
>  			break;
>  
>  		case OP_SRC_REG_INDIRECT:
> +			if (!cfi->drap && op->dest.reg == cfa->base) {

&& op->dest.reg == CFI_BP ?

> +
> +				/* mov disp(%rsp), %rbp */
> +				cfa->base = CFI_SP;
> +				cfa->offset = cfi->stack_size;
> +			}
> +
>  			if (cfi->drap && op->src.reg == CFI_BP &&
>  			    op->src.offset == cfi->drap_offset) {
>  
> @@ -2026,6 +2033,11 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
>  				/* mov disp(%rbp), %reg */
>  				/* mov disp(%rsp), %reg */
>  				restore_reg(cfi, op->dest.reg);
> +			} else if (op->src.reg == CFI_SP &&

An empty line above the else would help readability.

> +				   op->src.offset == regs[op->dest.reg].offset + cfi->stack_size) {
> +
> +				/* mov disp(%rsp), %reg */
> +				restore_reg(cfi, op->dest.reg);

>  			}
>  
>  			break;
> @@ -2103,6 +2115,11 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
>  			/* mov reg, disp(%rsp) */
>  			save_reg(cfi, op->src.reg, CFI_CFA,
>  				 op->dest.offset - cfi->cfa.offset);
> +		} else if (op->dest.reg == CFI_SP) {

Same here.

> +
> +			/* mov reg, disp(%rsp) */
> +			save_reg(cfi, op->src.reg, CFI_CFA,
> +				 op->dest.offset - cfi->stack_size);
>  		}
>  
>  		break;
> -- 
> 2.21.3
> 

-- 
Josh