Delve is a debugger for the Go programming language. We can debug and explore go program with it easily.
Installation
Delve can be installed by “go get”. After the installation, you can find it under $HOME/go. All we need to do is to add the folder “$HOME/go/bin” to $PATH.
go get -u github.com/derekparker/delve/cmd/dlv export PATH=$PATH:$HOME/go/bin
Usage
The following are 3 ways to debug go program with dlv.
dlv command.
dlv attach Attach to running process and begin debugging. dlv connect Connect to a headless debug server. dlv core Examine a core dump. dlv debug Compile and begin debugging main package in current directory, or the package specified. dlv exec Execute a precompiled binary, and begin a debug session. dlv help Help about any command dlv run Deprecated command. Use 'debug' instead. dlv test Compile test binary and begin debugging program. dlv trace Compile and begin tracing program. dlv version Prints version
dlv api
# start dlv with --headless at remote and use dlv ui to connect in local. dlv attach 18707 --headless --api-version=2 --log --listen=9.xx.xx.65:8181
# start gdlv to connect the remote debug. ➜ gdlv connect 9.xx.xx.65:8181
➜ bin ./dlv attach 18192 Type 'help' for list of commands. (dlv)
show available commands
(dlv) help The following commands are available: args ------------------------ Print function arguments. break (alias: b) ------------ Sets a breakpoint. breakpoints (alias: bp) ----- Print out info for active breakpoints. call ------------------------ Resumes process, injecting a function call (EXPERIMENTAL!!!) clear ----------------------- Deletes breakpoint. clearall -------------------- Deletes multiple breakpoints. condition (alias: cond) ----- Set breakpoint condition. config ---------------------- Changes configuration parameters. continue (alias: c) --------- Run until breakpoint or program termination. deferred -------------------- Executes command in the context of a deferred call. disassemble (alias: disass) - Disassembler. down ------------------------ Move the current frame down. edit (alias: ed) ------------ Open where you are in $DELVE_EDITOR or $EDITOR exit (alias: quit | q) ------ Exit the debugger. frame ----------------------- Set the current frame, or execute command on a different frame. funcs ----------------------- Print list of functions. goroutine ------------------- Shows or changes current goroutine goroutines ------------------ List program goroutines. help (alias: h) ------------- Prints the help message. list (alias: ls | l) -------- Show source code. locals ---------------------- Print local variables. next (alias: n) ------------- Step over to next source line. on -------------------------- Executes a command when a breakpoint is hit. print (alias: p) ------------ Evaluate an expression. regs ------------------------ Print contents of CPU registers. restart (alias: r) ---------- Restart process. set ------------------------- Changes the value of a variable. source ---------------------- Executes a file containing a list of delve commands sources --------------------- Print list of source files. stack (alias: bt) ----------- Print stack trace. step (alias: s) ------------- Single step through program. step-instruction (alias: si) Single step a single cpu instruction. stepout --------------------- Step out of the current function. thread (alias: tr) ---------- Switch to the specified thread. threads --------------------- Print out info for every traced thread. trace (alias: t) ------------ Set tracepoint. types ----------------------- Print list of types up -------------------------- Move the current frame up. vars ------------------------ Print package variables. whatis ---------------------- Prints type of an expression. Type help followed by a command for full documentation.
(dlv) goroutine 1 stack 0 0x0000000000428eac in runtime.gopark at /usr/lib/golang/src/runtime/proc.go:288 1 0x0000000000428f9e in runtime.goparkunlock at /usr/lib/golang/src/runtime/proc.go:293 2 0x00000000004429e0 in time.Sleep at /usr/lib/golang/src/runtime/time.go:65 3 0x0000000000489bf0 in main.main at /root/tmp/go/hello_world.go:9 4 0x0000000000428a06 in runtime.main at /usr/lib/golang/src/runtime/proc.go:195 5 0x0000000000451721 in runtime.goexit at /usr/lib/golang/src/runtime/asm_amd64.s:2337
(dlv) goroutine 2 stack 0 0x0000000000428eac in runtime.gopark at /usr/lib/golang/src/runtime/proc.go:288 1 0x0000000000428f9e in runtime.goparkunlock at /usr/lib/golang/src/runtime/proc.go:293 2 0x0000000000428ccc in runtime.forcegchelper at /usr/lib/golang/src/runtime/proc.go:245 3 0x0000000000451721 in runtime.goexit at /usr/lib/golang/src/runtime/asm_amd64.s:2337
(dlv) goroutine 19 stack 0 0x000000000040d582 in runtime.notetsleepg at /usr/lib/golang/src/runtime/lock_futex.go:227 1 0x00000000004431f5 in runtime.timerproc at /usr/lib/golang/src/runtime/time.go:216 2 0x0000000000451721 in runtime.goexit at /usr/lib/golang/src/runtime/asm_amd64.s:2337
show threads
(dlv) threads * Thread 18192 at 0x452bd3 /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 runtime.futex Thread 18193 at 0x452bd3 /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 runtime.futex Thread 18194 at 0x452bd3 /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 runtime.futex Thread 18195 at 0x452bd3 /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 runtime.futex Thread 18196 at 0x452bd3 /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 runtime.futex
list relevant source code
(dlv) l > runtime.futex() /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 (PC: 0x452bd3) 475: MOVQ ts+16(FP), R10 476: MOVQ addr2+24(FP), R8 477: MOVL val3+32(FP), R9 478: MOVL $202, AX 479: SYSCALL => 480: MOVL AX, ret+40(FP) 481: RET 482: 483: // int32 clone(int32 flags, void *stk, M *mp, G *gp, void (*fn)(void)); 484: TEXT runtime·clone(SB),NOSPLIT,$0 485: MOVL flags+0(FP), DI (dlv)
use up/down to go through the current frame.
(dlv) down > runtime.futex() /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 (PC: 0x452bd3) Frame 4: /usr/lib/golang/src/runtime/time.go:216 (PC: 4431f5) 211: // At least one timer pending. Sleep until then. 212: timers.sleeping = true 213: timers.sleepUntil = now + delta 214: noteclear(&timers.waitnote) 215: unlock(&timers.lock) => 216: notetsleepg(&timers.waitnote, delta) 217: } 218: } 219: 220: func timejump() *g { 221: if faketime == 0 { (dlv) up > runtime.futex() /usr/lib/golang/src/runtime/sys_linux_amd64.s:480 (PC: 0x452bd3) Frame 5: /usr/lib/golang/src/runtime/asm_amd64.s:2337 (PC: 451721) 2332: RET 2333: 2334: // The top-most function running on a goroutine 2335: // returns to goexit+PCQuantum. 2336: TEXT runtime·goexit(SB),NOSPLIT,$0-0 =>2337: BYTE $0x90 // NOP 2338: CALL runtime·goexit1(SB) // does not return 2339: // traceback from goexit1 must hit code range of goexit 2340: BYTE $0x90 // NOP 2341: 2342: TEXT runtime·prefetcht0(SB),NOSPLIT,$0-8 (dlv)
