Re: problem with System call!!

["Randy.Dunlap" <rddunlap@osdl.org>]

On Tue, 2 Apr 2002, Pavan Kumar Achanta wrote:

|    I was tring to implement the standard pedagogictime system
| call from 'nutt'.. It got compiled but got an error :

Hm, Apr-02.  Not a joke, right?

|    Error while loading shared libraries : libc.80.6   Cannot
| stat shared object: Error 14  /sbin/mingetty

Probably a syscall error due to a mangled syscall table...

|  when I restart with the new kernel image
|   And this is what I did .....

Was this from a diff/patch file, and it wouldn't apply cleanly?
(hint, hint)

| ********* step1 *******************
| /usr/src/linux/arch/i386/kernel/entry.S
|
| .data
| ENTRY(sys_call_table)
|     .long SYMBOL_NAME(sys_ni_syscall)   /* 0  -  old "setup()"
| system call*/
|     .long SYMBOL_NAME(sys_exit)
|     .long SYMBOL_NAME(sys_fork)
|     .long SYMBOL_NAME(sys_read)
|     .long SYMBOL_NAME(sys_write)
|     .long SYMBOL_NAME(sys_open)     /* 5 */
|
| 	..................
|
|     .long SYMBOL_NAME(sys_ni_syscall)       /* streams1 */
|     .long SYMBOL_NAME(sys_ni_syscall)       /* streams2 */
|     .long SYMBOL_NAME(sys_vfork)            /* 190 */
|
|     .long SYMBOL_NAME(sys_pedagogictime)    /* 191 */

This could have been correct when there were only 190 defined
syscalls.  When there are 221 syscalls, you should make
sys_pedagogictime be number 222, and larger if there are more
syscalls already defined.  I.e., don't stomp on current
syscalls.

|     .rept NR_syscalls-191  //change number -190 to -191
|         .long SYMBOL_NAME(sys_ni_syscall)
|     .endr
|
| it was NR_syscalls-221 and changed it to NR_syscalls-191

and this made syscalls 191-221 invalid ("ni" == not implemented).

| //********* step2 *******************
| And  one more line to file /usr/src/linux/include/asm/unistd.h
|
| #define __NR_sigaltstack    186
| #define __NR_sendfile       187
| #define __NR_getpmsg        188 /* some people actually want
| streams */
| #define __NR_putpmsg        189 /* some people actually want
| streams */
| #define __NR_vfork      190
| #define __NR_pedagogictime  191 /*Bill add this line for lab4 */

Use next available number, don't stomp on existing syscalls.

| Here I didnt know what to do about the already existing
| #define __NR_mmap  191  so I just kept it as it is..
|   Can somebody tell me what the line
|
|   .rept NR_syscalls-191  //change number -190 to -191
|         .long SYMBOL_NAME(sys_ni_syscall)
|     .endr

This just fills up the syscalls table with pointers to
"sys_ni_syscall", so that syscall numbers 191 thru NR_syscalls
will call the ni_syscall and return an error value to the caller.

|   means and how the whole thing works!!! and what is the right
| way to add a system call ....

Yeah, there should be a simple writeup on that somewhere.
Did you search for one?

I think that I've given you enough ammunition to take the next
step(s), without actually doing the work for you.

-- 
~Randy

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