Commit aafeb14e authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Support stack-swizzle 



Natively support the stack swizzle pattern:

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

It uses the vals[] array to link the first two stack-ops, and detect
the SP to SP_INDIRECT swizzle.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Acked-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
parent 2a512829

tools/objtool/check.c

+45 −0
Original line number Diff line number Diff line
@@ -1945,6 +1945,38 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi, 
					cfa->offset = -cfi->vals[op->src.reg].offset;

					cfi->stack_size = cfa->offset;



				} else if (cfa->base == CFI_SP &&

					   cfi->vals[op->src.reg].base == CFI_SP_INDIRECT &&

					   cfi->vals[op->src.reg].offset == cfa->offset) {



					/*

					 * Stack swizzle:

					 *

					 * 1: mov %rsp, (%[tos])

					 * 2: mov %[tos], %rsp

					 *    ...

					 * 3: pop %rsp

					 *

					 * Where:

					 *

					 * 1 - places a pointer to the previous

					 *     stack at the Top-of-Stack of the

					 *     new stack.

					 *

					 * 2 - switches to the new stack.

					 *

					 * 3 - pops the Top-of-Stack to restore

					 *     the original stack.

					 *

					 * Note: we set base to SP_INDIRECT

					 * here and preserve offset. Therefore

					 * when the unwinder reaches ToS it

					 * will dereference SP and then add the

					 * offset to find the next frame, IOW:

					 * (%rsp) + offset.

					 */

					cfa->base = CFI_SP_INDIRECT;



				} else {

					cfa->base = CFI_UNDEFINED;

					cfa->offset = 0;
@@ -2047,6 +2079,13 @@ static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi, 


		case OP_SRC_POP:

		case OP_SRC_POPF:

			if (op->dest.reg == CFI_SP && cfa->base == CFI_SP_INDIRECT) {



				/* pop %rsp; # restore from a stack swizzle */

				cfa->base = CFI_SP;

				break;

			}



			if (!cfi->drap && op->dest.reg == cfa->base) {



				/* pop %rbp */
@@ -2193,6 +2232,12 @@ 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->stack_size);



		} else if (op->src.reg == CFI_SP && op->dest.offset == 0) {



			/* mov %rsp, (%reg); # setup a stack swizzle. */

			cfi->vals[op->dest.reg].base = CFI_SP_INDIRECT;

			cfi->vals[op->dest.reg].offset = cfa->offset;

		}



		break;