时间：2021-07-01 10:21:17 帮助过：6人阅读
package dlsym
// #cgo CFLAGS: -I.
// #include <stddef.h>
// #include "dlsym_wrapper.h"
import "C"
import "unsafe"
func Intercept(symbol string) {
ptr := unsafe.Pointer(&([]byte(symbol)[0]))
C.intercept((*C.char)(ptr), C.size_t(len(symbol)))
}#include <dlfcn.h>
#include <stddef.h>
#include <stdio.h>
void intercept(char *symbol, size_t symbol_len) {
symbol = NULL; // will cause SIGSEGV
printf("%s\n", symbol);
fflush(stdout);
}go test -c github.com/taowen/go-lib c/dlsym
# will produce executable dlsym.test这个是用于分析coredump的时候获得符号表使用的。
GOTRACEBACK=crash ./dlsym.test
# produced /tmp/core_dlsym.test.29937如果找不到coredump的位置，执行之前先设置好coredump的写出条件
echo ‘/tmp/core_%e.%p‘ | sudo tee /proc/sys/kernel/core_pattern
ulimit -c unlimited # coredump can be any largegdb dlsym.test /tmp/core_dlsym.test /tmp/core_dlsym.test.29937用 bt full 查看所有的frame
用 frame <number> 查看指定的frame
用 print <symbol> 查看指定的变量的值
通过cgo调用C语言库时会出现程序崩溃的情况，于是就希望能够生成core文件来查看程序崩溃时的堆栈信息。那么Golang程序如何在崩溃后生成core文件呢？答案就是GOTRACEBACK这个环境变量。
关于GOTRACEBACK环境变量的详细说明，可以参考官方文档在runtime一节的链接，这里仅列出文档中较为核心的说明如下（Golang版本为1.6）。根据文档的说明我们可以知道GOTRACEBACK的可选值为：none、single、all、system和crash，其中关于crash的说明就指出了在Unix系统上，程序崩溃会通过SIGABRT信号触发一次core dump。 GOTRACEBACK=none omits the goroutine stack traces entirely. GOTRACEBACK=single (the default) behaves as described above. GOTRACEBACK=all adds stack traces for all user-created goroutines. GOTRACEBACK=system is like “all” but adds stack frames for run-time functions and shows goroutines created internally by the run-time. GOTRACEBACK=crash is like “system” but crashes in an operating system-specific manner instead of exiting. For example, on Unix systems, the crash raises SIGABRT to trigger a core dump. 另外，虽然官方文档给出了GOTRACEBACK环境变量在不同选值下的行为说明，但看起来实在是有些不知所云，这里我们不妨通过一个简单的程序来验证一下，毕竟程序跑出来的效果才比较真实。以下是验证程序的代码，其功能非常简单，启动两个goroutine，一个正常跑10秒钟，一个睡5秒钟之后自行panic。 package main import ( "fmt" "time" ) func saferoutine(c chan bool) { for i := 0; i < 10; i++ { fmt.Println("Count:", i) time.Sleep(1 * time.Second) } c <- true } func panicgoroutine(c chan bool) { time.Sleep(5 * time.Second) panic("Panic, omg ...") c <- true } func main() { c := make(chan bool, 2) go saferoutine(c) go panicgoroutine(c) for i := 0; i < 2; i++ { <-c } } 编译以上验证程序，然后在GOTRACEBACK取值为none的情况下执行，其结果如下。由此可知在取值为none时，程序仅仅打印出panic消息，之后程序就退出了。 # go build testgotraceback.go # env GOTRACEBACK=none ./testgotraceback Count: 0 Count: 1 Count: 2 Count: 3 Count: 4 panic: Panic, omg ... 以下为GOTRACEBACK取值为single情况下的执行结果，此时还会打印出发生panic的goroutine（也就是main.panicgoroutine）的调用栈信息，而single也是GOTRACEBACK的默认值。 # env GOTRACEBACK=single ./testgotraceback Count: 0 Count: 1 Count: 2 Count: 3 Count: 4 panic: Panic, omg ... goroutine 6 [running]: panic(0x4b8e00, 0xc82000a310) /home/ubuntu/repository/oo/go/src/runtime/panic.go:464 +0x3e6 main.panicgoroutine(0xc82004e070) /home/ubuntu/go/src/testcode/testgotraceback.go:18 +0x78 created by main.main /home/ubuntu/go/src/testcode/testgotraceback.go:25 +0x79 以下为GOTRACEBACK取值为all情况下的执行结果，此时不仅发生panic的goroutine（也就是main.panicgoroutine）的调用栈信息会被打印出来，主进程（main.main）和正常goroutine（也就是main.saferoutine）的调用栈信息也都被打印出来了。 # env GOTRACEBACK=all ./testgotraceback Count: 0 Count: 1 Count: 2 Count: 3 Count: 4 panic: Panic, omg ... goroutine 6 [running]: panic(0x4b8e00, 0xc82000a300) /home/ubuntu/repository/oo/go/src/runtime/panic.go:464 +0x3e6 main.panicgoroutine(0xc82004e070) /home/ubuntu/go/src/testcode/testgotraceback.go:18 +0x78 created by main.main /home/ubuntu/go/src/testcode/testgotraceback.go:25 +0x79 goroutine 1 [chan receive]: main.main() /home/ubuntu/go/src/testcode/testgotraceback.go:27 +0xa9 goroutine 5 [sleep]: time.Sleep(0x3b9aca00) /home/ubuntu/repository/oo/go/src/runtime/time.go:59 +0xf9 main.saferoutine(0xc82004e070) /home/ubuntu/go/src/testcode/testgotraceback.go:11 +0x177 created by main.main /home/ubuntu/go/src/testcode/testgotraceback.go:24 +0x57 以下为GOTRACEBACK取值为system情况下的执行结果，此时除了我们明显知道的三个goroutine的调用栈信息会被打印出来以外，很多隐形存在的系统级goroutine的信息也被打印出来了。因为本博主还不太了解Golang运行期机制，这里就不对这些系统级的goroutine一一做介绍了，但最明显的是有用来做垃圾回收的相关协程。 # env GOTRACEBACK=system ./testgotraceback Count: 0 Count: 1 Count: 2 Count: 3 Count: 4 panic: Panic, omg ... goroutine 6 [running]: panic(0x4b8e00, 0xc820064090) /home/ubuntu/repository/oo/go/src/runtime/panic.go:464 +0x3e6 fp=0xc820028778 sp=0xc8200286f8 main.panicgoroutine(0xc820056070) /home/ubuntu/go/src/testcode/testgotraceback.go:18 +0x78 fp=0xc8200287b8 sp=0xc820028778 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc8200287c0 sp=0xc8200287b8 created by main.main /home/ubuntu/go/src/testcode/testgotraceback.go:25 +0x79 goroutine 1 [chan receive]: runtime.gopark(0x52b150, 0xc8200560c8, 0x5005c0, 0xc, 0x17, 0x3) /home/ubuntu/repository/oo/go/src/runtime/proc.go:262 +0x163 fp=0xc82003de30 sp=0xc82003de08 runtime.goparkunlock(0xc8200560c8, 0x5005c0, 0xc, 0x17, 0x3) /home/ubuntu/repository/oo/go/src/runtime/proc.go:268 +0x54 fp=0xc82003de68 sp=0xc82003de30 runtime.chanrecv(0x4b4780, 0xc820056070, 0x0, 0xc82003df01, 0x400000) /home/ubuntu/repository/oo/go/src/runtime/chan.go:470 +0x49f fp=0xc82003def0 sp=0xc82003de68 runtime.chanrecv1(0x4b4780, 0xc820056070, 0x0) /home/ubuntu/repository/oo/go/src/runtime/chan.go:355 +0x2b fp=0xc82003df20 sp=0xc82003def0 main.main() /home/ubuntu/go/src/testcode/testgotraceback.go:27 +0xa9 fp=0xc82003df50 sp=0xc82003df20 runtime.main() /home/ubuntu/repository/oo/go/src/runtime/proc.go:188 +0x2b0 fp=0xc82003dfa0 sp=0xc82003df50 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc82003dfa8 sp=0xc82003dfa0 goroutine 2 [force gc (idle)]: runtime.gopark(0x52b150, 0x585640, 0x500ce0, 0xf, 0x14, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:262 +0x163 fp=0xc820026758 sp=0xc820026730 runtime.goparkunlock(0x585640, 0x500ce0, 0xf, 0xc820000314, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:268 +0x54 fp=0xc820026790 sp=0xc820026758 runtime.forcegchelper() /home/ubuntu/repository/oo/go/src/runtime/proc.go:229 +0xb8 fp=0xc8200267c0 sp=0xc820026790 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc8200267c8 sp=0xc8200267c0 created by runtime.init.4 /home/ubuntu/repository/oo/go/src/runtime/proc.go:218 +0x2b goroutine 3 [GC sweep wait]: runtime.gopark(0x52b150, 0x585760, 0x4ff370, 0xd, 0x41bf14, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:262 +0x163 fp=0xc820026f48 sp=0xc820026f20 runtime.goparkunlock(0x585760, 0x4ff370, 0xd, 0x14, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:268 +0x54 fp=0xc820026f80 sp=0xc820026f48 runtime.bgsweep(0xc820056000) /home/ubuntu/repository/oo/go/src/runtime/mgcsweep.go:63 +0xb1 fp=0xc820026fb8 sp=0xc820026f80 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc820026fc0 sp=0xc820026fb8 created by runtime.gcenable /home/ubuntu/repository/oo/go/src/runtime/mgc.go:191 +0x53 goroutine 4 [finalizer wait]: runtime.gopark(0x52b150, 0x59fc00, 0x500a40, 0xe, 0x14, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:262 +0x163 fp=0xc820027718 sp=0xc8200276f0 runtime.goparkunlock(0x59fc00, 0x500a40, 0xe, 0x14, 0x1) /home/ubuntu/repository/oo/go/src/runtime/proc.go:268 +0x54 fp=0xc820027750 sp=0xc820027718 runtime.runfinq() /home/ubuntu/repository/oo/go/src/runtime/mfinal.go:158 +0xaa fp=0xc8200277c0 sp=0xc820027750 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc8200277c8 sp=0xc8200277c0 created by runtime.createfing /home/ubuntu/repository/oo/go/src/runtime/mfinal.go:139 +0x60 goroutine 5 [sleep]: runtime.gopark(0x52b150, 0x585780, 0x4fded0, 0x5, 0x643513, 0x2) /home/ubuntu/repository/oo/go/src/runtime/proc.go:262 +0x163 fp=0xc82003ee80 sp=0xc82003ee58 runtime.goparkunlock(0x585780, 0x4fded0, 0x5, 0x13, 0x2) /home/ubuntu/repository/oo/go/src/runtime/proc.go:268 +0x54 fp=0xc82003eeb8 sp=0xc82003ee80 time.Sleep(0x3b9aca00) /home/ubuntu/repository/oo/go/src/runtime/time.go:59 +0xf9 fp=0xc82003ef00 sp=0xc82003eeb8 main.saferoutine(0xc820056070) /home/ubuntu/go/src/testcode/testgotraceback.go:11 +0x177 fp=0xc82003efa8 sp=0xc82003ef00 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc82003efb0 sp=0xc82003efa8 created by main.main /home/ubuntu/go/src/testcode/testgotraceback.go:24 +0x57 goroutine 7 [syscall]: runtime.notetsleepg(0x585798, 0x682c29, 0x0) /home/ubuntu/repository/oo/go/src/runtime/lock_futex.go:205 +0x4e fp=0xc820028f38 sp=0xc820028f10 runtime.timerproc() /home/ubuntu/repository/oo/go/src/runtime/time.go:209 +0xde fp=0xc820028fc0 sp=0xc820028f38 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc820028fc8 sp=0xc820028fc0 created by runtime.addtimerLocked /home/ubuntu/repository/oo/go/src/runtime/time.go:116 +0x11f 以下为GOTRACEBACK取值为crash情况下的执行结果，当然在执行之前我们需要修改core文件大小为unlimited，此时打印出来的内容与system的情况下基本一样，除了最后那行代表core dump的提示。另外，在当前目录下，我们想要的core文件出现了！所以在Linux系统下，crash与system的区别就是，前者可以生成core文件。 # ulimit -c unlimited # env GOTRACEBACK=crash ./testgotraceback ... goroutine 21 [runnable]: runtime.notetsleepg(0x585798, 0x11b22e, 0x0) /home/ubuntu/repository/oo/go/src/runtime/lock_futex.go:205 +0x4e fp=0xc820024738 sp=0xc820024710 runtime.timerproc() /home/ubuntu/repository/oo/go/src/runtime/time.go:209 +0xde fp=0xc8200247c0 sp=0xc820024738 runtime.goexit() /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc8200247c8 sp=0xc8200247c0 created by runtime.addtimerLocked /home/ubuntu/repository/oo/go/src/runtime/time.go:116 +0x11f Aborted (core dumped) # ls -l total 5400 -rw------- 1 ubuntu ubuntu 1994752 Apr 20 18:11 core -rwxrwxr-x 1 ubuntu ubuntu 2295416 Apr 20 17:38 testgotraceback -rw-rw-r-- 1 ubuntu ubuntu 395 Apr 20 17:38 testgotraceback.go 通过gdb命令，我们可以看到程序发生崩溃时的具体位置，这样即使崩溃点发生在C语言库中，也可以快速定位问题，简直就是so nice！ # gdb ./testgotraceback core (gdb) bt #0 runtime.raise () at /home/ubuntu/repository/oo/go/src/runtime/sys_linux_amd64.s:110 #1 0x0000000000438588 in runtime.dieFromSignal (sig=6) at /home/ubuntu/repository/oo/go/src/runtime/signal1_unix.go:192 #2 0x00000000004386af in runtime.crash () at /home/ubuntu/repository/oo/go/src/runtime/signal1_unix.go:247 #3 0x000000000042886e in runtime.dopanic_m (gp=0xc820001380, pc=4357542, sp=859530495736) at /home/ubuntu/repository/oo/go/src/runtime/panic.go:642 #4 0x000000000044ad72 in runtime.dopanic.func1 () at /home/ubuntu/repository/oo/go/src/runtime/panic.go:517 #5 0x0000000000453569 in runtime.systemstack () at /home/ubuntu/repository/oo/go/src/runtime/asm_amd64.s:291 #6 0x000000000042c6b0 in runtime.startTheWorldWithSema () at /home/ubuntu/repository/oo/go/src/runtime/proc.go:983 #7 0x000000c82001f500 in ?? () #8 0x0000000000000000 in ?? () 参考链接：http://dave.cheney.net/2015/11/29/a-whirlwind-tour-of-gos-runtime-environment-variablesGo -- 通过GOTRACEBACK生成程序崩溃后core文件的方法(gcore gdb)
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