[tip: objtool/core] objtool: Make SP memory operation match PUSH/POP semantics

[tip-bot2 for Julien Thierry]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     201ef5a974e24112953b74cc9f33dcfc4cbcc1cb
Gitweb:        https://git.kernel.org/tip/201ef5a974e24112953b74cc9f33dcfc4cbcc1cb
Author:        Julien Thierry <jthierry@xxxxxxxxxx>
AuthorDate:    Wed, 14 Oct 2020 08:38:02 +01:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 13 Jan 2021 18:13:10 -06:00

objtool: Make SP memory operation match PUSH/POP semantics

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@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 tools/objtool/check.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 00d00f9..270adc3 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2065,6 +2065,14 @@ 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) {
 
@@ -2086,6 +2094,12 @@ 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 &&
+				   op->src.offset == regs[op->dest.reg].offset + cfi->stack_size) {
+
+				/* mov disp(%rsp), %reg */
+				restore_reg(cfi, op->dest.reg);
 			}
 
 			break;
@@ -2163,6 +2177,12 @@ 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->cfa.offset);
+
+		} else if (op->dest.reg == CFI_SP) {
+
+			/* mov reg, disp(%rsp) */
+			save_reg(cfi, op->src.reg, CFI_CFA,
+				 op->dest.offset - cfi->stack_size);
 		}
 
 		break;