From d980302c518d4e442547bc862d23b07486bc5d59 Mon Sep 17 00:00:00 2001
From: clc5q <clc5q@git.zephyr-software.com>
Date: Wed, 24 Sep 2014 01:40:35 +0000
Subject: [PATCH] Avoid false positives by not instrumenting unsigned lea
reg3,[reg1-const] instructions.
Former-commit-id: 61af91c1d01f23cef0b0d30776315584b9000e93
---
libtransform/src/integertransform64.cpp | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/libtransform/src/integertransform64.cpp b/libtransform/src/integertransform64.cpp
index b69a451a0..f7e0e9942 100644
--- a/libtransform/src/integertransform64.cpp
+++ b/libtransform/src/integertransform64.cpp
@@ -750,7 +750,7 @@ void IntegerTransform64::addOverflowCheckNoFlag_RegTimesReg(Instruction_t *p_ins
}
// Example annotation to handle
-// 804852e 3 INSTR CHECK OVERFLOW NOFLAGSIGNED 32 EDX+EAX ZZ lea eax, [edx+eax] Reg1: EDX Reg2: EAX
+// 804852e 3 INSTR CHECK OVERFLOW NOFLAGSIGNED 32 EDX+EAX ZZ lea eax, [edx+k] Reg1: EDX Reg3: EAX
// Need to handle both 32-bit and 64-bit versions
//
// Original:
@@ -788,6 +788,12 @@ void IntegerTransform64::addOverflowCheckNoFlag_RegPlusConstant(Instruction_t *p
cerr << __func__ << ": r3 <-- r1+k: r1: " << Register::toString(p_reg1) << " k: " << p_constant << " target register: " << Register::toString(p_reg3) << " annotation: " << p_annotation.toString() << endl;
+ if (p_annotation.isUnsigned() && (p_constant < 0)) {
+ logMessage(__func__, "lea reg+neg constant pattern: skip this annotation type (prone to false positives)");
+ m_numOverflowsSkipped++;
+ return;
+ }
+
Instruction_t *origFallthrough = p_instruction->GetFallthrough();
Instruction_t *instr, *first, *saturation_policy;
Instruction_t *restore = addNewAssembly("popf");
@@ -817,13 +823,14 @@ void IntegerTransform64::addOverflowCheckNoFlag_RegPlusConstant(Instruction_t *p
instr->SetFallthrough(origFallthrough);
// Original code sequence:
- // lea r3, [r1+r2]
+ // lea r3, [r1+k]
// <originalNext>
//
// Instrumentation:
// push r1 ; save r1
// pushf ; save flags
// add r1, k ; r1 = r1 + k
+ // (or sub r1,-k ; r1 = r1 - (-k) for k < 0)
// <overflowcheck> ; check for overflow
// (jno|jnc <restore>) ; SIGNED|UNSIGNED
// fallthrough--><policy>
@@ -839,7 +846,14 @@ void IntegerTransform64::addOverflowCheckNoFlag_RegPlusConstant(Instruction_t *p
first->SetFallthrough(instr);
std::ostringstream s;
- s << "add " << Register::toString(p_reg1) << "," << p_constant;
+ if (p_constant >= 0) {
+ s << "add " << Register::toString(p_reg1) << "," << p_constant;
+ }
+ else {
+ // NOTE: We are short-circuiting this case currently; see top of
+ // this function. Should never get here.
+ s << "sub " << Register::toString(p_reg1) << "," << (-p_constant);
+ }
instr = addNewAssembly(instr, s.str());
if (p_annotation.isSigned())
{
--
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