Kernel linker and undefined references in KLD

[Kostik Belousov]

On Thu, Jul 15, 2010 at 10:13:54PM +0400, Dmitry Krivenok wrote:
> Unfortunately, one can easily miss such problems during build of the module.
> I'm working on a system which consists of lots of user-space programs
> and kernel modules and
> uses it's own complicated build system.
> gcc option -Werror is not used by the build system (I believe it
> should), that's why we just missed
> a compiler warning when called undeclared function (actually declared
> as static deep in kernel source).
> 
> Then we got kernel panic and started investigating it.
> I disassembled seltdinit function and found that it takes pointer to
> thread from %eax register and global kernel
> functions (e.g. kern_select) calling seltdinit copy the pointer to
> %eax just before "call" instruction.
> 
> Then I disassembled my own function calling seltdinit and found that
> it passes the pointer via stack and
> doesn't do anything with %eax register.
> 
> I'm not OS/compilers/ASM expert, but I guess that gcc is free to
> optimize passing of parameters to static functions
> because it has all the information about callers of these static
> functions (all stuff is inside one translation unit).
> So kernel functions call static functions in a right way, but modules
> compiled separately may use wrong calling
> convention.
Your message does not contain the question, but right answer is that
you should not call static functions.

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