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

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