Kernel symbols missing from /proc/kallsyms (kernel 3.4.88)

ManishSharma · 08-01-2014, 05:17 AM

/proc/kallsyms does not contain symbols like formats, sys_call_table, ia32_sys_call_table, tasklist_lock etc in Kernel 3.4.88.
In accordance, kallsyms_lookup_name() returns NULL addresses for such symbols.

Any suggestions on what could be the reason and how to work around this? Is there any particular Kernel Config responsible for this?

unSpawn · 08-02-2014, 01:43 AM

Quote:

Originally Posted by ManishSharma

/proc/kallsyms does not contain symbols like formats, sys_call_table, (..) in Kernel 3.4.88.

It does that since kernel 2.6.18 or thereabout IIRC.

Quote:

Originally Posted by ManishSharma

Any suggestions on what could be the reason

This was Linus' chosen method for flushing out any applications that think they legitimately need to access (let alone modify) it.

Quote:

Originally Posted by ManishSharma

Is there any particular Kernel Config responsible for this?

IIRC not.

Quote:

Originally Posted by ManishSharma

and how to work around this?

The above means you shouldn't be concerned with or interested in the syscall table. If you are then you have a particular reason (that might well violate Linus' decree or clash with legality otherwise) and you know kernel structs already so you should simply get it yourself. There's examples abound on the 'net anyway.

ManishSharma · 08-05-2014, 03:44 AM

Thanks unSpawn for your reply. Few more queries in case you can help..
I am able to see these symbols in 3.4.43 /proc.kallsyms! So I am wondering if some particular kernel config does this "selective" symbol hiding in 3.4.88?
And, infact kallsyms_lookup_name() is able to return address for tasklist_lock when the same is not available in 3.4.88 /proc/kallsyms!!
Also, any idea if it is OK to assume that addresses from /proc/kallsyms on a booted kernel would always be same as its System.map?