Are uninitialized static kernel variables set to NULL / 0?

[Avernar]

I've tracked down a kernel bug and want to fix it right away in my own kernel. Basically a function is being called twice and it is resetting a pair of global variables, a pointer and a size, to NULL and 0 respectively.

It's the ipfw_init_obj_rewriter function in ip_fw_sockopt.c which is getting called a second time when I launch a vnet jail. This causes the ipfw list command to segfault as the kernel stops returning table names. It also causes a small memory leak and I don't know what other issues.

If those variables are initialized to NULL and 0 automatically then I can just remove the two lines initializing them later. They look like they are but I want to make sure.

This is in 11.0-RC2

 

[Avernar]

Fixed the bug by changing where the functions are called in ip_fw2.c but I'd still like to know the answer to my question.

 

[tobik@]

They should be initialized with NULL or 0, see the C99 standard, section 6.7.8:

If an object that has static storage duration is not initialized explicitly, then:
— if it has pointer type, it is initialized to a null pointer;
— if it has arithmetic type, it is initialized to (positive or unsigned) zero;
— if it is an aggregate, every member is initialized (recursively) according to these rules;
— if it is a union, the first named member is initialized (recursively) according to these rules

with static storage duration meaning (6.7.4):

An object whose identifier is declared with external or internal linkage, or with the
storage-class specifier static has static storage duration. Its lifetime is the entire
execution of the program and its stored value is initialized only once, prior to program
startup.

 

[Avernar]

I know the C standard. The C run time library does that initialization.

However, I've encountered many embeded systems that have a very small C RTL that do not do this. And operating system kernels do not use the compiler's C RTL. The have their own custom start up and library routines.

So my question rephrased is: Does the Freebsd kernel's startup code do the C99 section 6.7.8 initialization?

 

[Juha Nurmela]

Vaaaguely related sidenote, you can do stuff like

#include <sys/cdefs.h>

int main __section(".bss");

to force variables in strange places.

Juha

It does, don't worry