"__floatsidf" undefined warning when compiling kernel module - c

Question

I was writing a loadable kernel module and when trying to compile it, the linker fails with the following message:
*** Warning: "__floatsidf" [/testing/Something.ko] undefined!
I am NOT using floating point variables, so that's not it. What is the cause of such errors?
Note: I'm using Linux ubuntu kernel v. 3.5.0-23-generic

Answer 1

__floatsidf is a runtime routine to convert a 32-bit signed integer into a double precision floating point number. Somewhere in your project is a line that looks like:
double foo = bar;
Or something similar, where bar is a 32-bit integer. It could also be that you're calling one of the libm functions (or any other function, really) that expects a double with an integer parameter:
foo = pow(bar, baz);
where either bar or baz (or both) is an integer.
Without showing some code, there's not much more we can do to help.
To narrow it down, check the object files your compiler generates (before you link them) and look in the disassembly for a reference to that symbol - that should tell you what function it's happening in.
Here's an example of what I mean. First up - source code:
#include <math.h>
int function(int x, int y)
{
return pow(x, y);
}
Pretty straightforward, right? Now, I'm going to compile it for ARM and disassemble:
$ clang -arch arm -O2 -c -o example.o example.c
$ otool -tV example.o
example.o:
(__TEXT,__text) section
_function:
00000000 e92d40f0 push {r4, r5, r6, r7, lr}
00000004 e28d700c add r7, sp, #12
00000008 e1a04001 mov r4, r1
0000000c ebfffffb bl ___floatsidf
00000010 e1a05000 mov r5, r0
00000014 e1a00004 mov r0, r4
00000018 e1a06001 mov r6, r1
0000001c ebfffff7 bl ___floatsidf
00000020 e1a02000 mov r2, r0
00000024 e1a03001 mov r3, r1
00000028 e1a00005 mov r0, r5
0000002c e1a01006 mov r1, r6
00000030 ebfffff2 bl _pow
00000034 ebfffff1 bl ___fixdfsi
00000038 e8bd40f0 pop {r4, r5, r6, r7, lr}
0000003c e12fff1e bx lr
Look at that - two calls to __floatsidf and one to __fixdfsi, matching the two conversions of x and y to double and then the conversion of the return type back to int.

Answer 2

You are using floating point somewhere - your module includes a conversion from int to double. It might be as simple as calling a function that takes a double parameter and passing an int.
You could try searching your code for "double".
You could try compiling your module to assembly code and looking at that to find which function uses __floatsidf.
Remember that the use of double might be in a header file, possibly one written by someone else.