In that case, the __builtin_return_address(level) level > 1 is not possible either ? what if the kernel uses this ?
Xin
On Wed, Jul 30, 2014 at 8:00 PM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote:
On Thu, Jul 31, 2014 at 12:59 AM, Xin Tong <trent.tong@xxxxxxxxx> wrote:
why can not __builtin_return_address() be made *never* inline and use current level+1 to get the return address of the function of interest. For any stack introspection, having 1 more level will not hurt functionality.Actually, the answer for your remark is "impossible" - in the case when the kernel is compiled without frame pointer. (CONFIG_FRAME_POINTER=n) which is true for certain variant of RHEL / CentOS. Without the availability of EBP on the stack, there is no way to know when to stop reading the stack to retrieve the previous stackframe. Of course u can statically walk the disassembly of the function and see how much stack space the particular function has allocated. But that requires implementing a disassembler in the kernel.
given its explanation below— Built-in Function: void * __builtin_return_address (unsigned int level)
This function returns the return address of the current function, or of one of its callers. The level argument is number of frames to scan up the call stack. A value of
0yields the return address of the current function, a value of1yields the return address of the caller of the current function, and so forth. When inlining the expected behavior is that the function returns the address of the function that is returned to. To work around this behavior use thenoinlinefunction attribute.
--
Regards,
Peter Teoh
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
