[Backtracing][WIP] Add some debug to track down problem in Linux CI.

Author: al45tair

stdlib/public/Backtracing/Backtrace.swift

@@ -472,7 +472,10 @@ public struct Backtrace: CustomStringConvertible, Sendable {
       path = "/proc/self/maps"
     }
 
+    print("Capturing images by reading \(path)")
+
     guard let procMaps = readString(from: path) else {
+      print("Failed to read \(path)")
       return []
     }
 
@@ -486,6 +489,9 @@ public struct Backtrace: CustomStringConvertible, Sendable {
     /#
     let lines = procMaps.split(separator: "\n")
 
+    print("Read \(lines.count) from \(path):")
+    print(procMaps)
+
     // Find all the mapped files and get high/low ranges
     var mappedFiles: [Substring:AddressRange] = [:]
     for line in lines {
@@ -547,6 +553,7 @@ public struct Backtrace: CustomStringConvertible, Sendable {
         var endOfText: Address = range.low
 
         if let image = try? Elf32Image(source: subSource) {
+          print("\(path) is an ELF32 image")
           theUUID = image.uuid
 
           for hdr in image.programHeaders {
@@ -556,6 +563,7 @@ public struct Backtrace: CustomStringConvertible, Sendable {
             }
           }
         } else if let image = try? Elf64Image(source: subSource) {
+          print("\(path) is an ELF64 image")
           theUUID = image.uuid
 
           for hdr in image.programHeaders {
@@ -566,6 +574,7 @@ public struct Backtrace: CustomStringConvertible, Sendable {
           }
         } else {
           // Not a valid ELF image
+          print("\(path) is not an ELF image")
           continue
         }
 

stdlib/public/Backtracing/SymbolicatedBacktrace.swift

@@ -473,12 +473,17 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
     // number programs once per frame, whereas we could just run them once
     // for all the addresses we're interested in.
 
+    print("Images: \(theImages)")
+
     for frame in backtrace.frames {
       let address = FileImageSource.Address(frame.adjustedProgramCounter)
       if let imageNdx = theImages.firstIndex(
            where: { address >= $0.baseAddress
                       && address < $0.endOfText }
          ) {
+        print("\(hex(address)): checking image \(imageNdx) \(theImages[imageNdx].name)")
+        print("\(hex(address)): path is \(theImages[imageNdx].path)")
+
         let relativeAddress = address - FileImageSource.Address(theImages[imageNdx].baseAddress)
         var symbol: Symbol = Symbol(imageIndex: imageNdx,
                                     imageName: theImages[imageNdx].name,
@@ -491,16 +496,20 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
         if elf32Image == nil && elf64Image == nil {
           if let source = try? FileImageSource(path: theImages[imageNdx].path) {
             if let elfImage = try? Elf32Image(source: source) {
+              print("\(hex(address)): found an ELF32 image")
               elf32Image = elfImage
               elf32Cache[imageNdx] = elfImage
             } else if let elfImage = try? Elf64Image(source: source) {
+              print("\(hex(address)): found an ELF64 image")
               elf64Image = elfImage
               elf64Cache[imageNdx] = elfImage
             }
           }
         }
 
         if let theSymbol = elf32Image?.lookupSymbol(address: relativeAddress) {
+          print("\(hex(address)): found \(theSymbol.name) in ELF32")
+
           var location = try? elf32Image!.sourceLocation(for: relativeAddress)
 
           for inline in elf32Image!.inlineCallSites(at: relativeAddress) {
@@ -524,6 +533,8 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
                           offset: theSymbol.offset,
                           sourceLocation: location)
         } else if let theSymbol = elf64Image?.lookupSymbol(address: relativeAddress) {
+          print("\(hex(address)): found \(theSymbol.name) in ELF64")
+
           var location = try? elf64Image!.sourceLocation(for: relativeAddress)
 
           for inline in elf64Image!.inlineCallSites(at: relativeAddress) {
@@ -547,6 +558,8 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
                           offset: theSymbol.offset,
                           sourceLocation: location)
         } else {
+          print("\(hex(address)): symbol lookup failed")
+
           symbol = Symbol(imageIndex: imageNdx,
                           imageName: theImages[imageNdx].name,
                           rawName: "<unknown>",
@@ -558,6 +571,8 @@ public struct SymbolicatedBacktrace: CustomStringConvertible {
         continue
       }
 
+      print("\(hex(address)): address not found in image")
+
       frames.append(Frame(captured: frame, symbol: nil))
     }
     #else