Kotlin Help

Debugging Kotlin/Native

Currently, the Kotlin/Native compiler produces debug info compatible with the DWARF 2 specification, so modern debugger tools can perform the following operations:

  • breakpoints

  • stepping

  • inspection of type information

  • variable inspection

Produce binaries with debug info with Kotlin/Native compiler

To produce binaries with the Kotlin/Native compiler, use the -g option on the command line.

0:b-debugger-fixes:minamoto@unit-703(0)# cat - > hello.kt fun main(args: Array<String>) { println("Hello world") println("I need your clothes, your boots and your motocycle") } 0:b-debugger-fixes:minamoto@unit-703(0)# dist/bin/konanc -g hello.kt -o terminator KtFile: hello.kt 0:b-debugger-fixes:minamoto@unit-703(0)# lldb terminator.kexe (lldb) target create "terminator.kexe" Current executable set to 'terminator.kexe' (x86_64). (lldb) b kfun:main(kotlin.Array<kotlin.String>) Breakpoint 1: where = terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) + 4 at hello.kt:2, address = 0x00000001000012e4 (lldb) r Process 28473 launched: '/Users/minamoto/ws/.git-trees/debugger-fixes/terminator.kexe' (x86_64) Process 28473 stopped * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #0: 0x00000001000012e4 terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) at hello.kt:2 1 fun main(args: Array<String>) { -> 2 println("Hello world") 3 println("I need your clothes, your boots and your motocycle") 4 } (lldb) n Hello world Process 28473 stopped * thread #1, queue = 'com.apple.main-thread', stop reason = step over frame #0: 0x00000001000012f0 terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) at hello.kt:3 1 fun main(args: Array<String>) { 2 println("Hello world") -> 3 println("I need your clothes, your boots and your motocycle") 4 } (lldb)

Breakpoints

Modern debuggers provide several ways to set a breakpoint, see below for a tool-by-tool breakdown:

lldb

  • by name

    (lldb) b -n kfun:main(kotlin.Array<kotlin.String>) Breakpoint 4: where = terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) + 4 at hello.kt:2, address = 0x00000001000012e4

-n is optional, this flag is applied by default

  • by location (filename, line number)

    (lldb) b -f hello.kt -l 1 Breakpoint 1: where = terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) + 4 at hello.kt:2, address = 0x00000001000012e4
  • by address

    (lldb) b -a 0x00000001000012e4 Breakpoint 2: address = 0x00000001000012e4
  • by regex, you might find it useful for debugging generated artifacts, like lambda etc. (where used # symbol in name).

    3: regex = 'main\(', locations = 1 3.1: where = terminator.kexe`kfun:main(kotlin.Array<kotlin.String>) + 4 at hello.kt:2, address = terminator.kexe[0x00000001000012e4], unresolved, hit count = 0

gdb

  • by regex

    (gdb) rbreak main( Breakpoint 1 at 0x1000109b4 struct ktype:kotlin.Unit &kfun:main(kotlin.Array<kotlin.String>);
  • by name unusable, because : is a separator for the breakpoint by location

    (gdb) b kfun:main(kotlin.Array<kotlin.String>) No source file named kfun. Make breakpoint pending on future shared library load? (y or [n]) y Breakpoint 1 (kfun:main(kotlin.Array<kotlin.String>)) pending
  • by location

    (gdb) b hello.kt:1 Breakpoint 2 at 0x100001704: file /Users/minamoto/ws/.git-trees/hello.kt, line 1.
  • by address

    (gdb) b *0x100001704 Note: breakpoint 2 also set at pc 0x100001704. Breakpoint 3 at 0x100001704: file /Users/minamoto/ws/.git-trees/hello.kt, line 2.

Stepping

Stepping functions works mostly the same way as for C/C++ programs.

Variable inspection

Variable inspections for var variables works out of the box for primitive types. For non-primitive types there are custom pretty printers for lldb in konan_lldb.py:

λ cat main.kt | nl 1 fun main(args: Array<String>) { 2 var x = 1 3 var y = 2 4 var p = Point(x, y) 5 println("p = $p") 6 } 7 data class Point(val x: Int, val y: Int) λ lldb ./program.kexe -o 'b main.kt:5' -o (lldb) target create "./program.kexe" Current executable set to './program.kexe' (x86_64). (lldb) b main.kt:5 Breakpoint 1: where = program.kexe`kfun:main(kotlin.Array<kotlin.String>) + 289 at main.kt:5, address = 0x000000000040af11 (lldb) r Process 4985 stopped * thread #1, name = 'program.kexe', stop reason = breakpoint 1.1 frame #0: program.kexe`kfun:main(kotlin.Array<kotlin.String>) at main.kt:5 2 var x = 1 3 var y = 2 4 var p = Point(x, y) -> 5 println("p = $p") 6 } 7 8 data class Point(val x: Int, val y: Int) Process 4985 launched: './program.kexe' (x86_64) (lldb) fr var (int) x = 1 (int) y = 2 (ObjHeader *) p = 0x00000000007643d8 (lldb) command script import dist/tools/konan_lldb.py (lldb) fr var (int) x = 1 (int) y = 2 (ObjHeader *) p = [x: ..., y: ...] (lldb) p p (ObjHeader *) $2 = [x: ..., y: ...] (lldb) script lldb.frame.FindVariable("p").GetChildMemberWithName("x").Dereference().GetValue() '1' (lldb)

Getting representation of the object variable (var) could also be done using the built-in runtime function Konan_DebugPrint (this approach also works for gdb, using a module of command syntax):

0:b-debugger-fixes:minamoto@unit-703(0)# cat ../debugger-plugin/1.kt | nl -p 1 fun foo(a:String, b:Int) = a + b 2 fun one() = 1 3 fun main(arg:Array<String>) { 4 var a_variable = foo("(a_variable) one is ", 1) 5 var b_variable = foo("(b_variable) two is ", 2) 6 var c_variable = foo("(c_variable) two is ", 3) 7 var d_variable = foo("(d_variable) two is ", 4) 8 println(a_variable) 9 println(b_variable) 10 println(c_variable) 11 println(d_variable) 12 } 0:b-debugger-fixes:minamoto@unit-703(0)# lldb ./program.kexe -o 'b -f 1.kt -l 9' -o r (lldb) target create "./program.kexe" Current executable set to './program.kexe' (x86_64). (lldb) b -f 1.kt -l 9 Breakpoint 1: where = program.kexe`kfun:main(kotlin.Array<kotlin.String>) + 463 at 1.kt:9, address = 0x0000000100000dbf (lldb) r (a_variable) one is 1 Process 80496 stopped * thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1 frame #0: 0x0000000100000dbf program.kexe`kfun:main(kotlin.Array<kotlin.String>) at 1.kt:9 6 var c_variable = foo("(c_variable) two is ", 3) 7 var d_variable = foo("(d_variable) two is ", 4) 8 println(a_variable) -> 9 println(b_variable) 10 println(c_variable) 11 println(d_variable) 12 } Process 80496 launched: './program.kexe' (x86_64) (lldb) expression -- (int32_t)Konan_DebugPrint(a_variable) (a_variable) one is 1(int32_t) $0 = 0 (lldb)

Known issues

  • performance of Python bindings.

Last modified: 04 February 2023