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
note
Supporting the DWARF 2 specification means that the debugger tool recognizes Kotlin as C89, because before the DWARF 5 specification, there is no identifier for the Kotlin language type in specification.
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)Modern debuggers provide several ways to set a breakpoint, see below for a tool-by-tool breakdown:
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 = 0x00000001000012e4by address
(lldb) b -a 0x00000001000012e4 Breakpoint 2: address = 0x00000001000012e4by 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
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>)) pendingby 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 functions works mostly the same way as for C/C++ programs.
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)performance of Python bindings.