gdb 分析core文件 小记

测试环境twemproxy进程突然出core退出，记录一下gdb分析过程

解析 coredump文件

bt -- 打印crash时的堆栈

# gdb /root/proxy/bin/twemproxy /tmp/cordump.file

(gdb) bt
#0  0x00007f9f3b0d4337 in ssignal () from /lib64/libc.so.6
#1  0x00007f9f3b0d5a28 in abort () from /lib64/libc.so.6
#2  0x000000000041e27b in nc_assert (cond=cond@entry=0x44ea8a "pr->type == MSG_REQ_REDIS_DEL", file=file@entry=0x44ea18 "nc_redis.c",
    line=line@entry=2387, panic=panic@entry=1) at nc_util.c:353
#3  0x0000000000428065 in redis_pre_coalesce (r=0x22aaf30) at nc_redis.c:2387
#4  0x000000000041443b in rsp_forward (msg=0x22aaf30, s_conn=0x2b36690, ctx=0x1c33570) at nc_response.c:289
#5  rsp_recv_done (ctx=0x1c33570, conn=0x2b36690, msg=0x22aaf30, nmsg=<optimized out>) at nc_response.c:345
#6  0x0000000000410926 in msg_parsed (msg=0x22aaf30, conn=0x2b36690, ctx=0x1c33570) at nc_message.c:803
#7  msg_parse (msg=0x22aaf30, conn=0x2b36690, ctx=0x1c33570) at nc_message.c:841
#8  msg_recv_chain (msg=0x22aaf30, conn=0x2b36690, ctx=0x1c33570) at nc_message.c:896
#9  msg_recv (ctx=0x1c33570, conn=0x2b36690) at nc_message.c:973
#10 0x000000000040ba44 in core_recv (conn=0x2b36690, ctx=0x1c33570) at nc_core.c:247
#11 core_core (ctx=0x1c33570, conn=0x2b36690, events=1) at nc_core.c:385
#12 0x000000000040bcbc in core_loop (ctx=ctx@entry=0x1c33570) at nc_core.c:446
#13 0x0000000000402b48 in nc_run (nci=0x65a0e0 <nci>) at nc.c:709
#14 main (argc=<optimized out>, argv=0x7fff5f1ee568) at nc.c:763

可以看到异常的时2层，进入到它的上一层，然后打印层2 显示的变量pr

(gdb) frame 3
#3  0x0000000000428065 in redis_pre_coalesce (r=0x22aaf30) at nc_redis.c:2387
2387    nc_redis.c: No such file or directory.
(gdb) p *pr
$1 = {c_tqe = {tqe_next = 0x1fb14a0, tqe_prev = 0x25dde00, trace = {lastfile = 0x4472d0 "nc_request.c", lastline = 307,
      prevfile = 0x4472d0 "nc_request.c", prevline = 329}}, s_tqe = {tqe_next = 0x0, tqe_prev = 0x0, trace = {
      lastfile = 0x4472d0 "nc_request.c", lastline = 340, prevfile = 0x4472d0 "nc_request.c", prevline = 316}}, m_tqe = {
    tqe_next = 0x0, tqe_prev = 0x0, trace = {lastfile = 0x4463e8 "nc_message.c", lastline = 1065, prevfile = 0x4463e8 "nc_message.c",
      prevline = 1012}}, id = 2984568133, peer = 0x22aaf30, owner = 0x28cb430, tmo_rbe = {left = 0x0, right = 0x0, parent = 0x0,
    key = 0, data = 0x0, color = 0 '00'}, mhdr = {stqh_first = 0x0, stqh_last = 0x28f3868}, mlen = 4357, state = 0, depth = 0,
  pos = 0x0, token = 0x0, parser = 0x423030 <redis_parse_req>, result = MSG_PARSE_OK, fragment = 0x428270 <redis_fragment>,
  add_auth = 0x4284c0 <redis_add_auth>, failure = 0x427f20 <redis_failure>, reply = 0x428890 <redis_reply>,
  pre_coalesce = 0x427f60 <redis_pre_coalesce>, post_coalesce = 0x428340 <redis_post_coalesce>, mbuf_get = 0x40d960 <mbuf_get>,
  type = MSG_REQ_REDIS_MSET, keys = 0x1f9f450, vlen = 0, end = 0x0, narg_start = 0x0, narg_end = 0x0, narg = 12, rnarg = 0, rnargs = {
    0, 0, 0}, rlen = 0, integer = 0, frag_owner = 0x2834e10, nfrag = 0, frag_id = 134161, nfrag_done = 0, frag_seq = 0x0, err = 0,
  error = 0, ferror = 0, request = 1, quit = 0, noreply = 0, noforward = 0, done = 1, fdone = 0, swallow = 0, redis = 1, mseterr = 0,
  ticket = 0, concurrent = 0, param_err = 0, start_tv = {tv_sec = 0, tv_usec = 0}, send_server_tv = {tv_sec = 1599718440,
    tv_usec = 23785}, recv_server_tv = {tv_sec = 0, tv_usec = 0}, dump_len = 0,
  dump_data = "DEL spring:session:expirations:1599718440000 w_limit:loanDistribution call('pexpire', KEYS[1], ARGV[2]); else    return nil; end", forward_server = {len = 19, data = 0x1f46ce0 "127.0.0.1:10021:1"}}

可以根据dump_data得到当时解析到的命令，只保留128字节

然后结合着函数一起看

可以看到，打印出来的pr->type 为 MSG_REQ_REDIS_MSET，但是却走到了mget和del类型指令的预解析流程中

接下来就得具体看代码看上层逻辑为这么走到了这一层