diff --git a/.gitignore b/.gitignore index 28e4053c..68c338f5 100644 --- a/.gitignore +++ b/.gitignore @@ -31,3 +31,6 @@ _book a.out .oracle_jre_usage + +# Delve +debug diff --git a/SUMMARY.md b/SUMMARY.md index 242ea66c..2e1f2df8 100644 --- a/SUMMARY.md +++ b/SUMMARY.md @@ -30,7 +30,8 @@ * [3.5. 控制流](ch3-asm/ch3-05-control-flow.md) * [3.6. 再论函数](ch3-asm/ch3-06-func-again.md) * [3.7. 例子:Goroutine ID](ch3-asm/ch3-07-goroutine-id.md) - * [3.8. 补充说明](ch3-asm/ch3-08-faq.md) + * [3.8. Delve调试器](ch3-asm/ch3-08-debug.md) + * [3.9. 补充说明](ch3-asm/ch3-09-faq.md) * [第四章 RPC和Protobuf](ch4-rpc/readme.md) * [4.1. RPC入门](ch4-rpc/ch4-01-rpc-intro.md) * [4.2. Protobuf](ch4-rpc/ch4-02-pb-intro.md) diff --git a/ch3-asm/ch3-08-debug.md b/ch3-asm/ch3-08-debug.md new file mode 100644 index 00000000..a9f5b2d4 --- /dev/null +++ b/ch3-asm/ch3-08-debug.md @@ -0,0 +1,331 @@ +# 3.8. Delve调试器 + +目前Go语言支持GDB、LLDB和Delve几种调试器。其中GDB是最早支持的调试工具,LLDB是macOS系统推荐的标准调试工具。但是GDB和LLDB对Go语言的专有特性都缺乏很大支持,而只有Delve是专门为Go语言设计开发的调试工具。而且Delve本身也是采用Go语言开发,对Windows平台也提供了一样的支持。本节我们基于Delve简单解释如何调试Go汇编程序。 + +## Delve入门 + +首先根据官方的文档正确安装Delve调试器。我们会先构造一个简单的Go语言代码,用于熟悉下Delve的简单用法。 + +创建main.go文件,main函数先通过循初始化一个切片,然后输出切片的内容: + +```go +package main + +import ( + "fmt" +) + +func main() { + nums := make([]int, 5) + for i := 0; i < len(nums); i++ { + nums[i] = i * i + } + fmt.Println(nums) +} +``` + +命令行进入包所在目录,然后输入`dlv debug`命令进入调试: + +``` +$ dlv debug +Type 'help' for list of commands. +(dlv) +``` + +输入help命令可以查看到Delve提供的调试命令列表: + +``` +(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. + 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. + disassemble (alias: disass) - Disassembler. + down ------------------------ Move the current frame down. + 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) +``` + +每个Go程序的入口是main.main函数,我们可以用break在此设置一个断点: + +``` +(dlv) break main.main +Breakpoint 1 set at 0x10ae9b8 for main.main() ./main.go:7 +``` + +然后通过breakpoints查看已经设置的所有断点: + +``` +(dlv) breakpoints +Breakpoint unrecovered-panic at 0x102a380 for runtime.startpanic() /usr/local/go/src/runtime/panic.go:588 (0) + print runtime.curg._panic.arg +Breakpoint 1 at 0x10ae9b8 for main.main() ./main.go:7 (0) +``` + +我们发现除了我们自己设置的main.main邯郸断点外,Delve内部已经为panic异常函数设置了一个断点。 + +然后就可以通过continue命令让程序运行到下一个断点处: + +``` +(dlv) continue +> main.main() ./main.go:7 (hits goroutine(1):1 total:1) (PC: 0x10ae9b8) + 2: + 3: import ( + 4: "fmt" + 5: ) + 6: +=> 7: func main() { + 8: nums := make([]int, 5) + 9: for i := 0; i < len(nums); i++ { + 10: nums[i] = i * i + 11: } + 12: fmt.Println(nums) +(dlv) +``` + +输入next命令单步执行进入main函数内部: + +``` +(dlv) next +> main.main() ./main.go:8 (PC: 0x10ae9cf) + 3: import ( + 4: "fmt" + 5: ) + 6: + 7: func main() { +=> 8: nums := make([]int, 5) + 9: for i := 0; i < len(nums); i++ { + 10: nums[i] = i * i + 11: } + 12: fmt.Println(nums) + 13: } +(dlv) +``` + +进入函数之后可以通过args和locals命令查看函数的参数和局部变量: + +``` +(dlv) args +(no args) +(dlv) locals +nums = []int len: 842350763880, cap: 17491881, nil +``` + +因为main函数没有参数,因此args命令没有任何输出。而locals命令则输出了局部变量nums切片的值:此时切片还未完成初始化,切片的底层指针为nil,长度和容量都是一个随机数值。 + +再次输入next命令单步执行后就可以查看到nums切片初始化之后的结果了: + +``` +(dlv) next +> main.main() ./main.go:9 (PC: 0x10aea12) + 4: "fmt" + 5: ) + 6: + 7: func main() { + 8: nums := make([]int, 5) +=> 9: for i := 0; i < len(nums); i++ { + 10: nums[i] = i * i + 11: } + 12: fmt.Println(nums) + 13: } +(dlv) locals +nums = []int len: 5, cap: 5, [...] +i = 17601536 +(dlv) +``` + +此时因为调试器已经到了for语句行,因此局部变量出现了还未初始化的循环迭代变量i。 + +下面我们通过组合使用break和condition命令,在循环内部设置一个条件断点,当循环变量i等于3时断点生效: + +``` +(dlv) break main.go:10 +Breakpoint 2 set at 0x10aea33 for main.main() ./main.go:10 +(dlv) condition 2 i==3 +(dlv) +``` + +然后通过continue执行到刚设置的条件断点,并且输出局部变量: + +``` +(dlv) continue +> main.main() ./main.go:10 (hits goroutine(1):1 total:1) (PC: 0x10aea33) + 5: ) + 6: + 7: func main() { + 8: nums := make([]int, 5) + 9: for i := 0; i < len(nums); i++ { +=> 10: nums[i] = i * i + 11: } + 12: fmt.Println(nums) + 13: } +(dlv) locals +nums = []int len: 5, cap: 5, [...] +i = 3 +(dlv) print nums +[]int len: 5, cap: 5, [0,1,4,0,0] +(dlv) +``` + +我们发现当循环变量i等于3时,nums切片的前3个元素已经正确初始化。 + +我们还可以通过stack查看当前执行函数的栈帧信息: + +``` +(dlv) stack +0 0x00000000010aea33 in main.main + at ./main.go:10 +1 0x000000000102bd60 in runtime.main + at /usr/local/go/src/runtime/proc.go:198 +2 0x0000000001053bd1 in runtime.goexit + at /usr/local/go/src/runtime/asm_amd64.s:2361 +(dlv) +``` + +或者通过goroutine和goroutines命令查看当前Goroutine相关的信息: + +``` +(dlv) goroutine +Thread 101686 at ./main.go:10 +Goroutine 1: + Runtime: ./main.go:10 main.main (0x10aea33) + User: ./main.go:10 main.main (0x10aea33) + Go: /usr/local/go/src/runtime/asm_amd64.s:258 runtime.rt0_go (0x1051643) + Start: /usr/local/go/src/runtime/proc.go:109 runtime.main (0x102bb90) +(dlv) goroutines +[4 goroutines] +* Goroutine 1 - User: ./main.go:10 main.main (0x10aea33) (thread 101686) + Goroutine 2 - User: /usr/local/go/src/runtime/proc.go:292 runtime.gopark (0x102c189) + Goroutine 3 - User: /usr/local/go/src/runtime/proc.go:292 runtime.gopark (0x102c189) + Goroutine 4 - User: /usr/local/go/src/runtime/proc.go:292 runtime.gopark (0x102c189) +(dlv) +``` + +最后完成调试工作后输入quit命令退出调试器。至此我们已经掌握了Delve调试器器的简单用法。 + +## 调试汇编程序 + +用Delve调试Go汇编程序的过程比调试Go语言程序更加简单。调试汇编程序时,我们需要时刻关注寄存器的状态,如果涉及函数调用或局部变量或参数还需要重点关注栈寄存器SP的状态。 + +为了编译演示,我们用汇编重新实现main函数,简单打印一个字符串: + +``` +#include "textflag.h" +#include "funcdata.h" + +// "Hello World!\n" +DATA text<>+0(SB)/8,$"Hello Wo" +DATA text<>+8(SB)/8,$"rld!\n" +GLOBL text<>(SB),NOPTR,$16 + +// func main() +TEXT ·main(SB), $16-0 + NO_LOCAL_POINTERS + MOVQ $text<>+0(SB), AX + MOVQ AX, (SP) + MOVQ $16, 8(SP) + CALL runtime·printstring(SB) + RET +``` + +然后依然用break命令在main函数设置断点,并且输入continue命令让调试器执行到断点位置停下: + +``` +(dlv) break main.main +Breakpoint 1 set at 0x105018f for main.main() ./main_amd64.s:10 +(dlv) continue +> main.main() ./main_amd64.s:10 (hits goroutine(1):1 total:1) (PC: 0x105018f) + 5: DATA text<>+0(SB)/8,$"Hello Wo" + 6: DATA text<>+8(SB)/8,$"rld!\n" + 7: GLOBL text<>(SB),NOPTR,$16 + 8: + 9: // func main() +=> 10: TEXT ·main(SB), $16-0 + 11: NO_LOCAL_POINTERS + 12: MOVQ $text<>+0(SB), AX + 13: MOVQ AX, (SP) + 14: MOVQ $16, 8(SP) + 15: CALL runtime·printstring(SB) +(dlv) +``` + +此时我们可以通过regs查看全部的寄存器状态: + +``` +(dlv) regs + rax = 0x0000000001050180 + rbx = 0x0000000000000000 + rcx = 0x000000c420000300 + rdx = 0x0000000001070bc0 + rdi = 0x000000c42007c020 + rsi = 0x0000000000000001 + rbp = 0x00007fffffe00000 + rsp = 0x000000c420049f80 + r8 = 0x7fffffffffffffff + r9 = 0xffffffffffffffff + r10 = 0x0000000000000100 + r11 = 0x0000000000000286 + r12 = 0x000000c41fffff7c + r13 = 0x0000000000000000 + r14 = 0x0000000000000178 + r15 = 0x0000000000000004 + rip = 0x000000000105018f + rflags = 0x0000000000000202 +... +(dlv) +``` + +因为AMD64的各种寄存器非常多,项目的信息中刻意省略了非通用的寄存器。如果再单步执行到13行时,可以发现AX寄存器值的变化。 + +``` +(dlv) regs + rax = 0x00000000010a4060 + rbx = 0x0000000000000000 + rcx = 0x000000c420000300 +... +(dlv) +``` + +因此我们可以推断汇编程序内部定义的`text<>`数据的地址为0x00000000010a4060。我们可以用过print命令来查看该内存内的数据: + +``` +(dlv) print *(*[5]byte)(uintptr(0x00000000010a4060)) +[5]uint8 [72,101,108,108,111] +(dlv) +``` + +我们可以发现输出的`[5]uint8 [72,101,108,108,111]`刚好是对应“Hello”字符串。通过类似的方法,我们可以通过查看SP对应的栈指针位置,然后查看栈中局部变量的值。 + +至此我们就掌握了Go汇编程序的简单调试技术。 diff --git a/ch3-asm/ch3-08-faq.md b/ch3-asm/ch3-09-faq.md similarity index 97% rename from ch3-asm/ch3-08-faq.md rename to ch3-asm/ch3-09-faq.md index 95551206..42866ef7 100644 --- a/ch3-asm/ch3-08-faq.md +++ b/ch3-asm/ch3-09-faq.md @@ -1,3 +1,3 @@ -# 3.8. 补充说明 +# 3.9. 补充说明 得益于Go语言的设计,Go汇编语言的优势也非常明显:跨操作系统、不同CPU之间的用法也非常相似、支持C语言预处理器、支持模块。同时Go汇编语言也存在很多不足:它不是一个独立的语言,底层需要依赖Go语言甚至操作系统;很多高级特性很难通过手工汇编完成。虽然Go语言官方尽量保持Go汇编语言简单,但是汇编语言是一个比较大的话题,大到足以写一本Go汇编语言的教程。本章的目的是让大家对Go汇编语言简单入门,在看到底层汇编代码的时候不会一头雾水,在某些遇到性能受限制的场合能够通过Go汇编突破限制。这只是一个开始,后续版本会继续完善。 diff --git a/vendor/gobook.examples/ch3-08-debug/hello-asm/main.go b/vendor/gobook.examples/ch3-08-debug/hello-asm/main.go new file mode 100644 index 00000000..9d143c04 --- /dev/null +++ b/vendor/gobook.examples/ch3-08-debug/hello-asm/main.go @@ -0,0 +1,7 @@ +// Copyright 2018 . All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package main + +func main() diff --git a/vendor/gobook.examples/ch3-08-debug/hello-asm/main_amd64.s b/vendor/gobook.examples/ch3-08-debug/hello-asm/main_amd64.s new file mode 100644 index 00000000..9fb90061 --- /dev/null +++ b/vendor/gobook.examples/ch3-08-debug/hello-asm/main_amd64.s @@ -0,0 +1,16 @@ +#include "textflag.h" +#include "funcdata.h" + +// "Hello World!\n" +DATA text<>+0(SB)/8,$"Hello Wo" +DATA text<>+8(SB)/8,$"rld!\n" +GLOBL text<>(SB),NOPTR,$16 + +// func main() +TEXT ·main(SB), $16-0 + NO_LOCAL_POINTERS + MOVQ $text<>+0(SB), AX + MOVQ AX, (SP) + MOVQ $16, 8(SP) + CALL runtime·printstring(SB) + RET diff --git a/vendor/gobook.examples/ch3-08-debug/hello/main.go b/vendor/gobook.examples/ch3-08-debug/hello/main.go new file mode 100644 index 00000000..1f9d5e89 --- /dev/null +++ b/vendor/gobook.examples/ch3-08-debug/hello/main.go @@ -0,0 +1,13 @@ +package main + +import ( + "fmt" +) + +func main() { + nums := make([]int, 5) + for i := 0; i < len(nums); i++ { + nums[i] = i * i + } + fmt.Println(nums) +}