debugserver

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Revision as of 13:38, 17 January 2014 by Kimcha (talk | contribs)
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debugserver is a console app that as server for remote gdb debugging. It is installed when a device is marked for development. It can be found in /Developer/usr/bin/debugserver. This is also the process invoked by Xcode to debug applications on the device.

Command line options

debugserver can be invoked with

debugserver [<options>] host:<port> [<prog-name> <arg1> <arg2> ...]

Where options can be:

Option Effect
-a process Attach debugserver to process. The process can be a pid or executable name.
-d integer Assign the waitfor-duration.
-f ? ?
-g Turn on debugging.
-i integer Assign the waitfor-interval.
-l filename Log to file. Set filename to stdout to log to standard output.
-t Use task ID instead of process ID.
-v Verbose.
-w ? ?
-x method
--launch=method
How to launch the program. Can be one of:
  • auto: Auto-detect the best launch method to use.
  • fork: Launch program using fork(2) and exec(3).
  • posix: Launch program using posix_spawn(2).
  • spring: Launch program via SpringBoard.
--lockdown Obtain parameters from lockdown (?)

Patching for process attaching

The vanilla debugserver cannot attach to any processes due to lack of entitlement to allow task_for_pid(). An entitlement must be inserted to the binary to allow this.

  • 0. cd ~
  • 1. Thin the binary because ldid does not support fat binaries:
lipo -thin armv6 /Developer/usr/bin/debugserver -output ~/debugserver
  • 2. Save for following as ent.xml:
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>com.apple.springboard.debugapplications</key>
	<true/>
	<key>get-task-allow</key>
	<true/>
	<key>task_for_pid-allow</key>
	<true/>
	<key>run-unsigned-code</key>
	<true/>
</dict>
</plist>
  • 3. Apply the entitlement with ldid:
ldid -Sent.xml debugserver


Alternative Instructions (64bit compatible)

Alternatively if you are on a mac with xcode installed you can follow Peter Steinberger's instructions to add entitlement's to the debugserver that comes with xcode. This will allow you to keep it as a fat binary, which will work on all devices including 64bit iPhone 5S.

You can find Peter's full slides here: https://speakerd.s3.amazonaws.com/presentations/43ca7dd05d120131795d129291fe58eb/Taking_Advantage_of_the_Runtime.pdf and https://speakerdeck.com/steipete/taking-advantage-of-the-runtime which contain more useful tips. Instructions for getting the debugserver to work start on slide 45.

I am not sure if you need an Apple developer membership and certificate to add the entitlements. If this fails for you, try the first method above.

  • 1. Mount xcode's developer disk image on your Mac and copy the debugserver binary to your working directory:
hdiutil attach /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/ DeviceSupport/7.0.3\ \(11B508\)/DeveloperDiskImage.dmg
cp /Volumes/DeveloperDiskImage/usr/bin/debugserver .
  • 2. Save for following as entitlements.plist:
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/ PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>com.apple.springboard.debugapplications</key> <true/>
	<key>run-unsigned-code</key>
	<true/>
	<key>get-task-allow</key> <true/> <key>task_for_pid-allow</key> <true/>
</dict> 
</plist>
  • 3. Apply the entitlement with codesign:
codesign -s - --entitlements entitlements.plist -f debugserver


Attaching to a process

  • 1. On the device, type:
./debugserver *:1234 -a "YouTube"

Example:

My-iPhone-5S:~ root# ./debugserver *:1234 -a "YouTube"
debugserver-300.2 for arm64.
Attaching to process YouTube...
Spawning general listening thread.
Spawning kqueue listening thread.
Listening to port 1234 for a connection from *...


  • 2. On your mac launch lldb and type the following commands:
platform select remote-ios
process connect connect://192.168.2.104:1234

Obviously, replace the IP with your device's IP

Example:

mbkim:Debug_Server Kim$ lldb
(lldb) platform select remote-ios
  Platform: remote-ios
 Connected: no
  SDK Path: "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/7.0"
 SDK Roots: [ 0] "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2"
[...]
 SDK Roots: [21] "/Users/Kim/Library/Developer/Xcode/iOS DeviceSupport/7.0.4 (11B554a)"
(lldb) process connect connect://192.168.2.104:1234
Process 2612 stopped
* thread #1: tid = 0x30d1e, 0x3ba51a84 libsystem_kernel.dylib`mach_msg_trap + 20, queue = 'com.apple.main-thread, stop reason = signal SIGSTOP
    frame #0: 0x3ba51a84 libsystem_kernel.dylib`mach_msg_trap + 20
libsystem_kernel.dylib`mach_msg_trap + 20:
-> 0x3ba51a84:  pop    {r4, r5, r6, r8}
   0x3ba51a88:  bx     lr

libsystem_kernel.dylib`mach_msg_overwrite_trap:
   0x3ba51a8c:  mov    r12, sp
   0x3ba51a90:  push   {r4, r5, r6, r8}
(lldb) po [[UIApplication sharedApplication] delegate]
<YTAppDelegate: 0x15e635a0>
(lldb) 

Debugging through USB instead of WiFi

If you find debugging through WiFi is a little slow or you need to debug an app while WiFi is off, you can use usbmuxd to connect through USB:

wget http://cgit.sukimashita.com/usbmuxd.git/snapshot/usbmuxd-1.0.8.tar.bz2
tar xjfv usbmuxd-1.0.8.tar.bz2
cd usbmuxd-1.0.8/python-client/
python tcprelay.py -t 1234:1234

Now all connections to localhost:1234 will be forwarded to your iPhone through USB to port 1234

Connecting lldb:

(lldb) process connect connect://localhost:1234
Process 2612 stopped
* thread #1: tid = 0x30d1e, 0x3ba51a84 libsystem_kernel.dylib`mach_msg_trap + 20, queue = 'com.apple.main-thread, stop reason = signal SIGSTOP
    frame #0: 0x3ba51a84 libsystem_kernel.dylib`mach_msg_trap + 20
libsystem_kernel.dylib`mach_msg_trap + 20:
-> 0x3ba51a84:  pop    {r4, r5, r6, r8}
   0x3ba51a88:  bx     lr

libsystem_kernel.dylib`mach_msg_overwrite_trap:
   0x3ba51a8c:  mov    r12, sp
   0x3ba51a90:  push   {r4, r5, r6, r8}
(lldb) po [[UIApplication sharedApplication] delegate]
<YTAppDelegate: 0x15e635a0>


Example session

  • 1. Copy MobileNotes to your Mac, e.g. to /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/Applications/MobileNotes.app/MobileNotes.
  • 2. On the device, type:
~/debugserver -x spring host:6789 /Applications/MobileNotes.app/MobileNotes

This will launch MobileNotes and wait for the remote debugger.

  • 3. Launch the debugger and attach it to the remote process:

If using GDB:

  • On your Mac, launch /Developer/Platforms/iPhoneOS.platform/Developer/usr/libexec/gdb/gdb-arm-apple-darwin.
  • Type the following in gdb:
set shlib-path-substitutions / /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/
file /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/Applications/MobileNotes.app/MobileNotes
target remote-macosx 192.168.1.101:6789

where 192.168.1.101 should be replaced by the actual IP address of your device. The remote debug connection is now complete.

If using LLDB:

  • On your Mac, launch lldb.
  • Type the following in lldb:
platform select remote-ios
process connect connect://192.168.1.101:6789
  • 4. Enter c to continue and do whatever you want.

References