Strace Simple

strace_simple

#include <stdio.h>
#include <fcntl.h>

int main()
{
    int x = open("/tmp/test.txt", O_WRONLY);
    return 0;
}



[vagrant@localhost vagrant]$ strace ./a.out
execve("./a.out", ["./a.out"], [/* 25 vars */]) = 0

#why did we need to know where the data section ended, we did nothing with it.
brk(0)                                  = 0x1d90000  

#Demand zero in 1 page, what are we putting there? Dont see address being used
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb608fbc000  

#Try to find this file, not there. File containing list ELF shared libraries to be loaded before the program
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory) 


#open file containing directories of shared libraris
open("/etc/ld.so.cache", O_RDONLY)      = 3 
#Find out how big it is
fstat(3, {st_mode=S_IFREG|0644, st_size=15866, ...}) = 0 
#memory map the entire file in privately
mmap(NULL, 15866, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fb608fb8000  
#close the file
close(3)                                = 0 

#open file pointing to glibc
open("/lib64/libc.so.6", O_RDONLY)      = 3  
#Read 832 bytes into a buffer
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\356\1\0\0\0\0\0"..., 832) = 832  
#find out how big it is
fstat(3, {st_mode=S_IFREG|0755, st_size=1921096, ...}) = 0  
#memory map more than the entire file in privately?
mmap(NULL, 3750152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fb608a0a000
mprotect(0x7fb608b94000, 2097152, PROT_NONE) = 0
mmap(0x7fb608d94000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x18a000) = 0x7fb608d94000
mmap(0x7fb608d99000, 18696, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fb608d99000
close(3)                                = 0


#clear three page, demand zero page in
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb608fb7000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb608fb6000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fb608fb5000
arch_prctl(ARCH_SET_FS, 0x7fb608fb6700) = 0
mprotect(0x7fb608d94000, 16384, PROT_READ) = 0
mprotect(0x7fb608fbd000, 4096, PROT_READ) = 0
munmap(0x7fb608fb8000, 15866)           = 0

#Trie to open the file
open("/tmp/test.txt", O_WRONLY)         = 3
#Exit
exit_group(0)                           = ?