From 32946b2d7c9953fd424b615be9350011e84c116a Mon Sep 17 00:00:00 2001
From: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Date: Mon, 17 May 2021 19:31:05 +0200
Subject: [PATCH] proc: correctly truncate the result of binary ops on integers
 (#2463)

Truncates the result of binary operations on integers to the size of
the resulting type.
Also rewrites convertInt to not require allocations.

Fixes #2454
---
 pkg/proc/eval.go                 | 27 +++++++++++++++------------
 pkg/proc/proc_unexported_test.go | 23 +++++++++++++++++++++++
 service/test/variables_test.go   |  4 ++++
 3 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/pkg/proc/eval.go b/pkg/proc/eval.go
index 1313a514..fa35095d 100644
--- a/pkg/proc/eval.go
+++ b/pkg/proc/eval.go
@@ -3,7 +3,6 @@ package proc
 import (
 	"bytes"
 	"debug/dwarf"
-	"encoding/binary"
 	"errors"
 	"fmt"
 	"go/ast"
@@ -905,17 +904,14 @@ func (scope *EvalScope) evalTypeCast(node *ast.CallExpr) (*Variable, error) {
 }
 
 func convertInt(n uint64, signed bool, size int64) uint64 {
-	buf := make([]byte, 64/8)
-	binary.BigEndian.PutUint64(buf, n)
-	m := 64/8 - int(size)
-	s := byte(0)
-	if signed && (buf[m]&0x80 > 0) {
-		s = 0xff
+	bits := uint64(size) * 8
+	mask := uint64((1 << bits) - 1)
+	r := n & mask
+	if signed && (r>>(bits-1)) != 0 {
+		// sign extension
+		r |= ^uint64(0) &^ mask
 	}
-	for i := 0; i < m; i++ {
-		buf[i] = s
-	}
-	return uint64(binary.BigEndian.Uint64(buf))
+	return r
 }
 
 func (scope *EvalScope) evalBuiltinCall(node *ast.CallExpr) (*Variable, error) {
@@ -1636,8 +1632,15 @@ func (scope *EvalScope) evalBinary(node *ast.BinaryExpr) (*Variable, error) {
 
 		r := xv.newVariable("", 0, typ, scope.Mem)
 		r.Value = rc
-		if r.Kind == reflect.String {
+		switch r.Kind {
+		case reflect.String:
 			r.Len = xv.Len + yv.Len
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			n, _ := constant.Int64Val(r.Value)
+			r.Value = constant.MakeInt64(int64(convertInt(uint64(n), true, typ.Size())))
+		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+			n, _ := constant.Uint64Val(r.Value)
+			r.Value = constant.MakeUint64(convertInt(n, false, typ.Size()))
 		}
 		return r, nil
 	}
diff --git a/pkg/proc/proc_unexported_test.go b/pkg/proc/proc_unexported_test.go
index 62327ea8..ce269475 100644
--- a/pkg/proc/proc_unexported_test.go
+++ b/pkg/proc/proc_unexported_test.go
@@ -73,3 +73,26 @@ func TestAlignAddr(t *testing.T) {
 		c(example.align, example.in+0x10000, example.tgt+0x10000)
 	}
 }
+
+func TestConvertInt(t *testing.T) {
+	var testCases = []struct {
+		in     uint64
+		signed bool
+		size   int64
+		tgt    uint64
+	}{
+		{1, false, 1, 1},
+		{uint64(0xf0), true, 1, 0xfffffffffffffff0},
+		{uint64(0xf0), false, 1, 0xf0},
+		{uint64(0x70), true, 1, 0x70},
+		{uint64(0x90f0), true, 2, 0xffffffffffff90f0},
+		{uint64(0x90f0), false, 2, 0x90f0},
+	}
+	for _, tc := range testCases {
+		out := convertInt(tc.in, tc.signed, tc.size)
+		t.Logf("in=%#016x signed=%v size=%d -> %#016x\n", tc.in, tc.signed, tc.size, out)
+		if out != tc.tgt {
+			t.Errorf("expected=%#016x got=%#016x\n", tc.tgt, out)
+		}
+	}
+}
diff --git a/service/test/variables_test.go b/service/test/variables_test.go
index 4bab82a9..a40e9710 100644
--- a/service/test/variables_test.go
+++ b/service/test/variables_test.go
@@ -836,6 +836,10 @@ func TestEvalExpression(t *testing.T) {
 		{`iface2map.(data)`, false, "…", "…", "map[string]interface {}", nil},
 
 		{"issue1578", false, "main.Block {cache: *main.Cache nil}", "main.Block {cache: *main.Cache nil}", "main.Block", nil},
+		{"ni8 << 2", false, "-20", "-20", "int8", nil},
+		{"ni8 << 8", false, "0", "0", "int8", nil},
+		{"ni8 >> 1", false, "-3", "-3", "int8", nil},
+		{"bytearray[0] * bytearray[0]", false, "144", "144", "uint8", nil},
 	}
 
 	ver, _ := goversion.Parse(runtime.Version())