[PATCH v4 5/9] perf annotate: Invalidate register states for untracked instructions

[Zecheng Li <zecheng@google.com>]

When tracking variable types, instructions that modify a pointer value
in an untracked way can lead to incorrect type propagation. To prevent
this, invalidate the register state when encountering such instructions.

This change invalidates pointer types for various arithmetic and bitwise
operations that current pointer offset tracking doesn't support, like
imul, shl, and, inc, etc.

A special case is added for 'xor reg, reg', which is a common idiom for
zeroing a register. For this, the register state is updated to be a
constant with a value of 0.

This could introduce slight regressions if a variable is zeroed and then
reused. This can be addressed in the future by using all DWARF locations
for instruction tracking instead of only the first one.

Signed-off-by: Zecheng Li <zecheng@google.com>
---
 tools/perf/arch/x86/annotate/instructions.c | 29 +++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/perf/arch/x86/annotate/instructions.c b/tools/perf/arch/x86/annotate/instructions.c
index 0c87e42ca3dc..803f9351a3fb 100644
--- a/tools/perf/arch/x86/annotate/instructions.c
+++ b/tools/perf/arch/x86/annotate/instructions.c
@@ -427,6 +427,35 @@ static void update_insn_state_x86(struct type_state *state,
 		return;
 	}
 
+	/* Invalidate register states for other ops which may change pointers */
+	if (has_reg_type(state, dst->reg1) && !dst->mem_ref &&
+	    dwarf_tag(&state->regs[dst->reg1].type) == DW_TAG_pointer_type) {
+		if (!strncmp(dl->ins.name, "imul", 4) || !strncmp(dl->ins.name, "mul", 3) ||
+		    !strncmp(dl->ins.name, "idiv", 4) || !strncmp(dl->ins.name, "div", 3) ||
+		    !strncmp(dl->ins.name, "shl", 3)  || !strncmp(dl->ins.name, "shr", 3) ||
+		    !strncmp(dl->ins.name, "sar", 3)  || !strncmp(dl->ins.name, "and", 3) ||
+		    !strncmp(dl->ins.name, "or", 2)   || !strncmp(dl->ins.name, "neg", 3) ||
+		    !strncmp(dl->ins.name, "inc", 3)  || !strncmp(dl->ins.name, "dec", 3)) {
+			pr_debug_dtp("%s [%x] invalidate reg%d\n",
+						dl->ins.name, insn_offset, dst->reg1);
+			state->regs[dst->reg1].ok = false;
+			state->regs[dst->reg1].copied_from = -1;
+			return;
+		}
+
+		if (!strncmp(dl->ins.name, "xor", 3) && dst->reg1 == src->reg1) {
+			/* xor reg, reg clears the register */
+			pr_debug_dtp("xor [%x] clear reg%d\n",
+				     insn_offset, dst->reg1);
+
+			state->regs[dst->reg1].kind = TSR_KIND_CONST;
+			state->regs[dst->reg1].imm_value = 0;
+			state->regs[dst->reg1].ok = true;
+			state->regs[dst->reg1].copied_from = -1;
+			return;
+		}
+	}
+
 	if (strncmp(dl->ins.name, "mov", 3))
 		return;
 
-- 
2.51.0.788.g6d19910ace-goog