Handle 64-bit negative addresses when adjusting them. (#397)

Fixes #280. 64-bit addresses with the high bit set should be adjustable
as long as the offset does not overflow the result. This change
supersedes #396 avoiding `math/big` dependency.

internal/symbolz/symbolz.go

@@ -111,9 +111,9 @@ func symbolizeMapping(source string, offset int64, syms func(string, string) ([]
 	for _, l := range p.Location {
 		if l.Mapping == m && l.Address != 0 && len(l.Line) == 0 {
 			// Compensate for normalization.
-			addr := int64(l.Address) + offset
-			if addr < 0 {
-				return fmt.Errorf("unexpected negative adjusted address, mapping %v source %d, offset %d", l.Mapping, l.Address, offset)
+			addr, overflow := adjust(l.Address, offset)
+			if overflow {
+				return fmt.Errorf("cannot adjust address %d by %d, it would overflow (mapping %v)", l.Address, offset, l.Mapping)
 			}
 			a = append(a, fmt.Sprintf("%#x", addr))
 		}
@@ -144,15 +144,15 @@ func symbolizeMapping(source string, offset int64, syms func(string, string) ([]
 		}
 
 		if symbol := symbolzRE.FindStringSubmatch(l); len(symbol) == 3 {
-			addr, err := strconv.ParseInt(symbol[1], 0, 64)
+			origAddr, err := strconv.ParseUint(symbol[1], 0, 64)
 			if err != nil {
 				return fmt.Errorf("unexpected parse failure %s: %v", symbol[1], err)
 			}
-			if addr < 0 {
-				return fmt.Errorf("unexpected negative adjusted address, source %s, offset %d", symbol[1], offset)
-			}
 			// Reapply offset expected by the profile.
-			addr -= offset
+			addr, overflow := adjust(origAddr, -offset)
+			if overflow {
+				return fmt.Errorf("cannot adjust symbolz address %d by %d, it would overflow", origAddr, -offset)
+			}
 
 			name := symbol[2]
 			fn := functions[name]
@@ -166,7 +166,7 @@ func symbolizeMapping(source string, offset int64, syms func(string, string) ([]
 				p.Function = append(p.Function, fn)
 			}
 
-			lines[uint64(addr)] = profile.Line{Function: fn}
+			lines[addr] = profile.Line{Function: fn}
 		}
 	}
 
@@ -181,3 +181,20 @@ func symbolizeMapping(source string, offset int64, syms func(string, string) ([]
 
 	return nil
 }
+
+// adjust shifts the specified address by the signed offset. It returns the
+// adjusted address. It signals that the address cannot be adjusted without an
+// overflow by returning true in the second return value.
+func adjust(addr uint64, offset int64) (uint64, bool) {
+	adj := uint64(int64(addr) + offset)
+	if offset < 0 {
+		if adj >= addr {
+			return 0, true
+		}
+	} else {
+		if adj < addr {
+			return 0, true
+		}
+	}
+	return adj, false
+}

internal/symbolz/symbolz_test.go

@@ -16,6 +16,7 @@ package symbolz
 
 import (
 	"fmt"
+	"math"
 	"strings"
 	"testing"
 
@@ -139,3 +140,30 @@ func fetchSymbols(source, post string) ([]byte, error) {
 	}
 	return []byte(symbolz), nil
 }
+
+func TestAdjust(t *testing.T) {
+	for _, tc := range []struct {
+		addr         uint64
+		offset       int64
+		wantAdj      uint64
+		wantOverflow bool
+	}{{math.MaxUint64, 0, math.MaxUint64, false},
+		{math.MaxUint64, 1, 0, true},
+		{math.MaxUint64 - 1, 1, math.MaxUint64, false},
+		{math.MaxUint64 - 1, 2, 0, true},
+		{math.MaxInt64 + 1, math.MaxInt64, math.MaxUint64, false},
+		{0, 0, 0, false},
+		{0, -1, 0, true},
+		{1, -1, 0, false},
+		{2, -1, 1, false},
+		{2, -2, 0, false},
+		{2, -3, 0, true},
+		{-math.MinInt64, math.MinInt64, 0, false},
+		{-math.MinInt64 + 1, math.MinInt64, 1, false},
+		{-math.MinInt64 - 1, math.MinInt64, 0, true},
+	} {
+		if adj, overflow := adjust(tc.addr, tc.offset); adj != tc.wantAdj || overflow != tc.wantOverflow {
+			t.Errorf("adjust(%d, %d) = (%d, %t), want (%d, %t)", tc.addr, tc.offset, adj, overflow, tc.wantAdj, tc.wantOverflow)
+		}
+	}
+}