Merge pull request #14 from p-x9/feature/closest-symbol-info

Sources/MachOKit/MachOImage+Symbols.swift

@@ -140,7 +140,7 @@ extension MachOImage.Symbols64 {
                 nextIndex += 1
             }
 
-            var symbol = symbols.advanced(by: nextIndex).pointee
+            let symbol = symbols.advanced(by: nextIndex).pointee
             let str = stringBase
                 .advanced(by: numericCast(symbol.n_un.n_strx))
             let address = addressStart + numericCast(symbol.n_value)

Sources/MachOKit/MachOImage.swift

@@ -419,3 +419,24 @@ extension MachOImage {
         return nil
     }
 }
+
+extension MachOImage {
+    /// Find the symbol closest to the address.
+    ///
+    /// Behaves almost identically to the `dladdr` function
+    ///
+    /// - Parameters:
+    ///   - address: Address to find closest symbol.
+    ///   - sectionNumber: Section number to be searched.
+    /// - Returns: Closest symbol.
+    public func closestSymbol(
+        at address: UnsafeRawPointer,
+        inSection sectionNumber: Int = 0
+    ) -> Symbol? {
+        let offset = Int(bitPattern: address) - Int(bitPattern: ptr)
+        return closestSymbol(
+            at: offset,
+            inSection: sectionNumber
+        )
+    }
+}

Sources/MachOKit/Model/Symbol/Nlist.swift

@@ -11,6 +11,7 @@ import Foundation
 public protocol NlistProtocol: LayoutWrapper {
     var flags: SymbolFlags? { get }
     var symbolDescription: SymbolDescription? { get }
+    var sectionNumber: Int? { get }
 }
 
 public struct Nlist: NlistProtocol {
@@ -25,6 +26,10 @@ public struct Nlist: NlistProtocol {
     public var symbolDescription: SymbolDescription? {
         .init(rawValue: numericCast(layout.n_desc))
     }
+
+    public var sectionNumber: Int? {
+        layout.n_sect == NO_SECT ? nil : numericCast(layout.n_sect)
+    }
 }
 
 public struct Nlist64: NlistProtocol {
@@ -39,4 +44,8 @@ public struct Nlist64: NlistProtocol {
     public var symbolDescription: SymbolDescription? {
         .init(rawValue: numericCast(layout.n_desc))
     }
+
+    public var sectionNumber: Int? {
+        layout.n_sect == NO_SECT ? nil : numericCast(layout.n_sect)
+    }
 }

Sources/MachOKit/Protocol/MachORepresentable.swift

@@ -88,6 +88,16 @@ public protocol MachORepresentable {
     var weakBindingSymbols: [BindingSymbol] { get }
     var lazyBindingSymbols: [BindingSymbol] { get }
     var rebases: [Rebase] { get }
+
+    /// Find the symbol closest to the address at the specified offset.
+    ///
+    /// Behaves almost identically to the `dladdr` function
+    ///
+    /// - Parameters:
+    ///   - offset: Offset from start of mach header. (``SymbolProtocol.offset``)
+    ///   - sectionNumber: Section number to be searched.
+    /// - Returns: Closest symbol.
+    func closestSymbol(at offset: Int, inSection sectionNumber: Int) -> Symbol?
 }
 
 extension MachORepresentable {
@@ -166,3 +176,66 @@ extension MachORepresentable {
         return rebaseOperations.rebases(is64Bit: is64Bit)
     }
 }
+
+extension MachORepresentable {
+    public func closestSymbol(
+        at offset: Int,
+        inSection sectionNumber: Int = 0
+    ) -> Symbol? {
+        let symbols = Array(self.symbols)
+        var bestSymbol: Symbol?
+
+        if let dysym = loadCommands.dysymtab {
+            // find closest match in globals
+            let globalStart: Int = numericCast(dysym.iextdefsym)
+            let globalCount: Int = numericCast(dysym.nextdefsym)
+            for i in globalStart ..< globalStart + globalCount {
+                let symbol = symbols[i]
+                let nlist = symbol.nlist
+                let symbolSectionNumber = symbol.nlist.sectionNumber
+
+                guard nlist.flags?.type == .sect,
+                      symbol.offset <= offset,
+                      sectionNumber == 0 || symbolSectionNumber == sectionNumber,
+                      bestSymbol == nil || bestSymbol!.offset < symbol.offset else {
+                    continue
+                }
+                bestSymbol = symbol
+            }
+
+            // find closest match in locals
+            let localStart: Int = numericCast(dysym.ilocalsym)
+            let localCount: Int = numericCast(dysym.nlocalsym)
+            for i in localStart ..< localStart + localCount {
+                let symbol = symbols[i]
+                let nlist = symbol.nlist
+                let symbolSectionNumber = symbol.nlist.sectionNumber
+
+                guard nlist.flags?.type == .sect,
+                      nlist.flags?.stab == nil,
+                      symbol.offset <= offset,
+                      sectionNumber == 0 || symbolSectionNumber == sectionNumber,
+                      bestSymbol == nil || bestSymbol!.offset < symbol.offset else {
+                    continue
+                }
+                bestSymbol = symbol
+            }
+        } else {
+            // find closest match in locals
+            for symbol in symbols {
+                let nlist = symbol.nlist
+                let symbolSectionNumber = symbol.nlist.sectionNumber
+                guard nlist.flags?.type == .sect,
+                      nlist.flags?.stab == nil,
+                      symbol.offset <= offset,
+                      sectionNumber == 0 || symbolSectionNumber == sectionNumber,
+                      bestSymbol == nil || bestSymbol!.offset < symbol.offset else {
+                    continue
+                }
+                bestSymbol = symbol
+            }
+        }
+
+        return bestSymbol
+    }
+}

Tests/MachOKitTests/MachOFilePrintTests.swift

@@ -355,3 +355,27 @@ extension MachOFilePrintTests {
         }
     }
 }
+
+extension MachOFilePrintTests {
+    func testClosestSymbol() {
+        for symbol in machO.symbols {
+            let offset = symbol.offset + Int.random(in: 0..<100)
+            guard let best = machO.closestSymbol(
+                at: offset
+            ) else {
+                continue
+            }
+
+            let diff = best.offset - offset
+
+            print(
+                offset == best.offset,
+                symbol.offset == best.offset,
+                symbol.name == best.name,
+                symbol.name,
+                best.name,
+                diff
+            )
+        }
+    }
+}

Tests/MachOKitTests/MachOPrintTests.swift

@@ -330,3 +330,42 @@ extension MachOPrintTests {
         }
     }
 }
+
+extension MachOPrintTests {
+    func testClosestSymbol() {
+        for symbol in machO.symbols {
+            let offset = symbol.offset + Int.random(in: 0..<100)
+            guard let best = machO.closestSymbol(
+                at: offset
+            ) else {
+                continue
+            }
+
+            let diff = best.offset - offset
+
+            var info = Dl_info()
+            let isSucceeded = dladdr(machO.ptr.advanced(by: offset), &info) != 0
+            if !isSucceeded { print("failed") }
+
+            guard let dli_saddr = info.dli_saddr,
+                  let dli_sname = info.dli_sname else {
+                print("[dladdr is nil]", best.name, diff)
+                continue
+            }
+
+            XCTAssertEqual(
+                dli_saddr,
+                machO.ptr.advanced(by: best.offset)
+            )
+
+            print(
+                offset == best.offset,
+                dli_saddr == machO.ptr.advanced(by: offset),
+                dli_saddr == machO.ptr.advanced(by: best.offset),
+                strcmp(best.nameC + 1, dli_sname),
+                best.name,
+                diff
+            )
+        }
+    }
+}