Merge "Add a tool to inject data into an elf, macho, or PE symbol"

cmd/symbol_inject/Android.bp

@@ -0,0 +1,23 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+blueprint_go_binary {
+    name: "symbol_inject",
+    srcs: [
+        "symbol_inject.go",
+        "elf.go",
+        "macho.go",
+        "pe.go",
+    ],
+}

cmd/symbol_inject/elf.go

@@ -0,0 +1,76 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"debug/elf"
+	"fmt"
+	"io"
+)
+
+func findElfSymbol(r io.ReaderAt, symbol string) (uint64, uint64, error) {
+	elfFile, err := elf.NewFile(r)
+	if err != nil {
+		return maxUint64, maxUint64, cantParseError{err}
+	}
+
+	symbols, err := elfFile.Symbols()
+	if err != nil {
+		return maxUint64, maxUint64, err
+	}
+
+	for _, s := range symbols {
+		if elf.ST_TYPE(s.Info) != elf.STT_OBJECT {
+			continue
+		}
+		if s.Name == symbol {
+			offset, err := calculateElfSymbolOffset(elfFile, s)
+			if err != nil {
+				return maxUint64, maxUint64, err
+			}
+			return offset, s.Size, nil
+		}
+	}
+
+	return maxUint64, maxUint64, fmt.Errorf("symbol not found")
+}
+
+func calculateElfSymbolOffset(file *elf.File, symbol elf.Symbol) (uint64, error) {
+	if symbol.Section == elf.SHN_UNDEF || int(symbol.Section) >= len(file.Sections) {
+		return maxUint64, fmt.Errorf("invalid section index %d", symbol.Section)
+	}
+	section := file.Sections[symbol.Section]
+	switch file.Type {
+	case elf.ET_REL:
+		// "In relocatable files, st_value holds a section offset for a defined symbol.
+		// That is, st_value is an offset from the beginning of the section that st_shndx identifies."
+		return file.Sections[symbol.Section].Addr + symbol.Value, nil
+	case elf.ET_EXEC, elf.ET_DYN:
+		// "In executable and shared object files, st_value holds a virtual address. To make these
+		// files’ symbols more useful for the dynamic linker, the section offset (file interpretation)
+		// gives way to a virtual address (memory interpretation) for which the section number is
+		// irrelevant."
+		if symbol.Value < section.Addr {
+			return maxUint64, fmt.Errorf("symbol starts before the start of its section")
+		}
+		section_offset := symbol.Value - section.Addr
+		if section_offset+symbol.Size > section.Size {
+			return maxUint64, fmt.Errorf("symbol extends past the end of its section")
+		}
+		return section.Offset + section_offset, nil
+	default:
+		return maxUint64, fmt.Errorf("unsupported elf file type %d", file.Type)
+	}
+}

cmd/symbol_inject/macho.go

@@ -0,0 +1,65 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"debug/macho"
+	"fmt"
+	"io"
+)
+
+func findMachoSymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
+	machoFile, err := macho.NewFile(r)
+	if err != nil {
+		return maxUint64, maxUint64, cantParseError{err}
+	}
+
+	// TODO(ccross): why?
+	symbolName = "_" + symbolName
+
+	for i, symbol := range machoFile.Symtab.Syms {
+		if symbol.Sect == 0 {
+			continue
+		}
+		if symbol.Name == symbolName {
+			var nextSymbol *macho.Symbol
+			if i+1 < len(machoFile.Symtab.Syms) {
+				nextSymbol = &machoFile.Symtab.Syms[i+1]
+			}
+			return calculateMachoSymbolOffset(machoFile, symbol, nextSymbol)
+		}
+	}
+
+	return maxUint64, maxUint64, fmt.Errorf("symbol not found")
+}
+
+func calculateMachoSymbolOffset(file *macho.File, symbol macho.Symbol, nextSymbol *macho.Symbol) (uint64, uint64, error) {
+	section := file.Sections[symbol.Sect-1]
+
+	var end uint64
+	if nextSymbol != nil && nextSymbol.Sect != symbol.Sect {
+		nextSymbol = nil
+	}
+	if nextSymbol != nil {
+		end = nextSymbol.Value
+	} else {
+		end = section.Addr + section.Size
+	}
+
+	size := end - symbol.Value - 1
+	offset := uint64(section.Offset) + (symbol.Value - section.Addr)
+
+	return offset, size, nil
+}

cmd/symbol_inject/pe.go

@@ -0,0 +1,67 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"debug/pe"
+	"fmt"
+	"io"
+	"sort"
+)
+
+func findPESymbol(r io.ReaderAt, symbolName string) (uint64, uint64, error) {
+	peFile, err := pe.NewFile(r)
+	if err != nil {
+		return maxUint64, maxUint64, cantParseError{err}
+	}
+
+	sort.Slice(peFile.Symbols, func(i, j int) bool {
+		if peFile.Symbols[i].SectionNumber != peFile.Symbols[j].SectionNumber {
+			return peFile.Symbols[i].SectionNumber < peFile.Symbols[j].SectionNumber
+		}
+		return peFile.Symbols[i].Value < peFile.Symbols[j].Value
+	})
+
+	for i, symbol := range peFile.Symbols {
+		if symbol.Name == symbolName {
+			var nextSymbol *pe.Symbol
+			if i+1 < len(peFile.Symbols) {
+				nextSymbol = peFile.Symbols[i+1]
+			}
+			return calculatePESymbolOffset(peFile, symbol, nextSymbol)
+		}
+	}
+
+	return maxUint64, maxUint64, fmt.Errorf("symbol not found")
+}
+
+func calculatePESymbolOffset(file *pe.File, symbol *pe.Symbol, nextSymbol *pe.Symbol) (uint64, uint64, error) {
+	section := file.Sections[symbol.SectionNumber-1]
+
+	var end uint32
+	if nextSymbol != nil && nextSymbol.SectionNumber != symbol.SectionNumber {
+		nextSymbol = nil
+	}
+	if nextSymbol != nil {
+		end = nextSymbol.Value
+	} else {
+		end = section.Size
+	}
+
+	size := end - symbol.Value - 1
+	offset := section.Offset + symbol.Value
+
+	return uint64(offset), uint64(size), nil
+}