Re: please help

["Peter Teoh" <htmldeveloper at gmail dot com>]

first to use systemtap, u need to roughly know which kernel APIs u
want to trace.   to do that, u can use "strace" to trace the userspace
execution of the program, and from the system call output, (usually
:-)) add the sys_xxx to derive the kernel API version, eg, for
execve() it is sys_execve():

The following is your program:

/root>strace ./a.out
execve("./a.out", ["./a.out"], [/* 28 vars */]) = 0
brk(0)                                  = 0x804a000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb7ef5000
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=54870, ...}) = 0
mmap2(NULL, 54870, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7ee7000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/tls/i686/cmov/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\0\0`\1\000"...,
512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=1307104, ...}) = 0
mmap2(NULL, 1312164, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE,
3, 0) = 0xb7da6000
mmap2(0xb7ee1000, 12288, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x13b) = 0xb7ee1000
mmap2(0xb7ee4000, 9636, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7ee4000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb7da5000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb7da56c0,
limit:1048575, seg_32bit:1, contents:0, read_exec_only:0,
limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb7ee1000, 4096, PROT_READ)   = 0
munmap(0xb7ee7000, 54870)               = 0
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb7ef4000
write(1, "Test kernel", 11Test kernel)             = 11
exit_group(11)                          = ?

And sys_execve() in arch/x86/kernel/process_32.c is your start (mine
kernel is 2.6.20).   Well, it will be a long long path towards full
understanding even of this simple program.   Alternatively, pick a
topic of interest, and understand in greater depth about it.   Eg,
tracing the filesystem VFS APIs etc.

On Sat, Oct 11, 2008 at 10:12 PM, siddharam suresh
<siddharam.s.t@gmail.com> wrote:
> i want visualize what all the stuffs happening inside the Linux kernel
> when this program is executed
>
>
> #include<stdio.h>
> void main()
> {
> printf("Test kernel");  <-- here i want know what are all the system
> calls and the kernel data structure kernel is used by the kernel. Is
> it possible to put break points here and can we see what are the
> things happening inside the kernel when printf is executed
>
> }
>
>
> is it possible to put break points in side the my program using the
> system tap i want to visualize what are system calls and kernel data
> structure used by particular statement.
>
> as above stated test.c program i what see what is happening inside the
> kernel when printf("Test Kernel"); is executed .This because when the
> my program become large it will show so many information which may not
> be use full to me and very difficult to get the particular
> information.Is there any facilities like step in and step out in
> system tap
>
>
>
> thank you in advance
> waiting great response
>



-- 
Regards,
Peter Teoh