ltrace能夠跟蹤進程的庫函數調用,它會顯現出哪個庫函數被調用,而strace則是跟蹤程序的每個系統調用.
下面是一個ltrace與strace的對比
1)系統調用的輸出對比
我們用輸出hello world的程序做如下測試:
#include <stdio.h>
int
main ()
{
printf("Hello world!\n");
return 0;
}
gcc hello.c -o hello
用ltrace跟蹤hello程序,如下:
ltrace ./hello
__libc_start_main(0x8048354, 1, 0xbf869aa4, 0x8048390, 0x8048380 <unfinished ...>
puts("Hello world!"Hello world!
) = 13
+++ exited (status 0) +++
注:我們看到程序調用了puts();庫函數做了輸出.
用strace跟蹤hello程序,如下:
strace ./hello
execve("./hello", ["./hello"], [/* 30 vars */]) = 0
brk(0) = 0x83d4000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f8a000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=80846, ...}) = 0
mmap2(NULL, 80846, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7f76000
close(3) = 0
open("/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0000?\270"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1576952, ...}) = 0
mmap2(0xb6e000, 1295780, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb6e000
mmap2(0xca5000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x137) = 0xca5000
mmap2(0xca8000, 9636, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xca8000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f75000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7f756c0, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xca5000, 8192, PROT_READ) = 0
mprotect(0xb6a000, 4096, PROT_READ) = 0
munmap(0xb7f76000, 80846) = 0
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f89000
write(1, "Hello world!\n", 13Hello world!
) = 13
exit_group(0) = ?
Process 2874 detached
注:我們看到程序調用write()系統調用做了輸出,同時strace還把hello程序運行時所做的系統調用都打印出來了.
同樣的ltrace也可以把系統調用都打印出來,如下:
ltrace -S ./hello
SYS_execve(NULL, NULL, NULL) = 0xffffffda
SYS_brk(NULL) = -38
SYS_mmap2(0, 4096, 3, 34, -1) = -38
SYS_access(0xb6798f, 4, 0xb6afc0, 0, 0xb6b6b4) = -38
SYS_open("/etc/ld.so.cache", 0, 00) = -38
SYS_fstat64(3, 0xbfba5414, 0xb6afc0, -1, 3) = -38
SYS_mmap2(0, 80846, 1, 2, 3) = -38
SYS_close(3) = -38
SYS_open("/lib/libc.so.6", 0, 027756452364???, 512) = -38
SYS_read(3, ) = -38
SYS_fstat64(3, 0xbfba5478, 0xb6afc0, 4, 1) = -38
SYS_mmap2(0xb6e000, 0x13c5a4, 5, 2050, 3) = -38
SYS_mmap2(0xca5000, 12288, 3, 2066, 3) = -38
SYS_mmap2(0xca8000, 9636, 3, 50, -1) = -38
SYS_close(3) = -38
SYS_mmap2(0, 4096, 3, 34, -1) = -38
SYS_set_thread_area(0xbfba5960, 0xb7f5e6c0, 243, 0xb6afc0, 0) = -38
SYS_mprotect(0xca5000, 8192, 1, 7676, 0xca6e74) = -38
SYS_mprotect(0xb6a000, 4096, 1, 896, 0) = -38
SYS_munmap(0xb7f5f000, 80846 <unfinished ...>
__libc_start_main(0x8048354, 1, 0xbfba5dd4, 0x8048390, 0x8048380 <unfinished ...>
puts("Hello world!" <unfinished ...>
SYS_fstat64(1, 0xbfba5c20, 0xca6ff4, 0xca74c0, 0xca74c0) = 0
SYS_mmap2(0, 4096, 3, 34, -1) = 0xb7f72000
SYS_write(1, "Hello world!\n", 13Hello world!
) = 13
<... puts resumed> ) = 13
SYS_exit_group(0 <no return ...>
+++ exited (status 0) +++
注:我們看到它實際是用SYS_write系統調用來做打印輸出,其實write()函數是SYS_write的封裝,SYS_write是真正的系統調用.
二)ltrace/strace的耗時
ltrace -c dd if=/dev/urandom of=/dev/null count=1000
1000+0 records in
1000+0 records out
512000 bytes (512 kB) copied, 2.31346 seconds, 221 kB/s
% time seconds usecs/call calls function
------ ----------- ----------- --------- --------------------
84.88 4.942763 4942 1000 read
9.41 0.548195 548 1000 write
5.06 0.294716 294 1001 memcpy
0.11 0.006365 2121 3 __fprintf_chk
0.09 0.004969 4969 1 dcgettext
0.08 0.004850 808 6 strlen
0.05 0.002667 2667 1 setlocale
0.04 0.002579 644 4 sigaction
0.03 0.001869 467 4 close
0.03 0.001825 912 2 open64
0.03 0.001519 759 2 malloc
0.02 0.001187 593 2 __sprintf_chk
0.02 0.001176 588 2 clock_gettime
0.02 0.001169 389 3 __errno_location
0.02 0.001012 506 2 dcngettext
0.01 0.000814 814 1 lseek64
0.01 0.000757 757 1 getopt_long
0.01 0.000744 744 1 textdomain
0.01 0.000742 247 3 strchr
0.01 0.000634 634 1 __strtoull_internal
0.01 0.000602 602 1 getpagesize
0.01 0.000542 271 2 localeconv
0.01 0.000340 340 1 fclose
0.01 0.000300 300 1 memmove
0.00 0.000228 114 2 sigismember
0.00 0.000184 184 1 getenv
0.00 0.000170 85 2 sigaddset
0.00 0.000148 74 2 free
0.00 0.000093 93 1 bindtextdomain
0.00 0.000090 90 1 sigemptyset
0.00 0.000090 90 1 __cxa_atexit
0.00 0.000088 88 1 __ctype_b_loc
0.00 0.000074 74 1 __fpending
------ ----------- ----------- --------- --------------------
100.00 5.823501 3057 total
注:
使用-c選項,ltrace輸出由進程創建的庫調用,輸出結果以調用過程的時間為准進行排序,因為是從urandom設備上讀,這是一種產生隨機數的設備,完成后,寫入null設備.
所以讀過程花費了較多的時間.
使用ltrace去捕獲運行時函數,就好像在進程上系上了一個調試工具,它占據了ltrace大量的時間,這里ltrace一共消耗了5.8秒
我們再來看一下strace所花費的時間,如下:
strace -c dd if=/dev/urandom of=/dev/null count=1000
1000+0 records in
1000+0 records out
512000 bytes (512 kB) copied, 0.894482 seconds, 572 kB/s
Process 3049 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
82.85 0.159393 159 1005 read
15.07 0.028995 29 1003 write
0.78 0.001494 1494 1 execve
0.42 0.000814 136 6 rt_sigaction
0.23 0.000446 41 11 1 close
0.23 0.000435 73 6 fstat64
0.21 0.000412 32 13 mmap2
0.21 0.000408 29 14 6 open
0.00 0.000000 0 1 1 access
0.00 0.000000 0 3 brk
0.00 0.000000 0 2 munmap
0.00 0.000000 0 1 uname
0.00 0.000000 0 4 mprotect
0.00 0.000000 0 1 _llseek
0.00 0.000000 0 1 rt_sigprocmask
0.00 0.000000 0 1 getrlimit
0.00 0.000000 0 1 set_thread_area
0.00 0.000000 0 1 set_tid_address
0.00 0.000000 0 2 clock_gettime
0.00 0.000000 0 1 set_robust_list
------ ----------- ----------- --------- --------- ----------------
100.00 0.192397 2078 8 total
注:
strace一共消耗了0.19秒,strace把性能提升了30倍,這主要是strace在跟蹤系統調用的時候不需要動態庫,而ltrace是根據動態庫來分析程序運行的.
所以ltrace也只能跟蹤動態庫,不能跟蹤靜態庫.
事實上我們用ltrace和strace都可以發現程序在哪個系統調用時發生了性能瓶徑.
ltrace用-T,而strace也用-T.
三)ltrace與strace的相同點
ltrace與strace都可以指定PID,即對運行中的程序進行跟蹤.
ltrace -p PID與strace -p PID
ltrace與strace都可以跟蹤程序fork或clone子進程.
ltrace是用-f參數,而strace是用-f(fork/clone)和-F(vfork).