ABI stability in Kernel

Motivation

We would like to guarantee the KBI stability between minor version.

To achieve this, the first step is to having a tool so that we can check if the ABI of two binary are different.

Tool: CTFDiff

Differential: D48199

A tool that input two binary and compare their .SUNW_ctf section to check if their ABI is different.

Usage

In Base

Since all components in based is compiled with CTF, we can use the following command to check if two binary have different ABI

ctfdiff /boot/kernel/kernel /boot/kernel.old/kernel

Other

To use ctfdiff outside the base, we have to generate the .SUNW_ctf section manually:

First, compile your code with -g -c to generate dwarf information:

Notice that ctfconvert only support in single compile unit (e.g. relocatable file). So -c is needed

Here are two example code you can try:

# a.c

int var_a_have;

int var_both_same;

int var_both_diff;

int func_a_have() {
        return (0);
}

int func_both_diff() {
        return (0);
}

int func_both_same(int a, int b) {
        return (0);
}

int func_const_diff(int a) {
        return (0);
}

# b.c

int var_b_have;

int var_both_same;

double var_both_diff;


int func_b_have() {
        return (0);
}

int func_both_diff(int val) {
        return (0);
}

int func_both_same(int a, int b) {
        return (0);
}

int func_const_diff(const int a) {
        return (0);
}

clang -g -c a.c -o a.o
clang -g -c b.c -o b.o

Second, conver the dwarf to ctf with ctfconvert.

You have to provide a label name for the abi.

ctfconvert -l abi -o a a.o
ctfconvert -l abi -o b b.o

Last, Use ctfdiff to compare two files

ctfdiff a b

An example output is as following:

< means this symbol is from file at left hand side, > means this symbol is from file at right hand side.

< [0] func_a_have
> [0] func_b_have
< [1] func_both_diff
> [1] func_both_diff
< [3] func_const_diff
> [3] func_const_diff
< [0] var_a_have
> [0] var_b_have
< [2] var_both_diff
> [2] var_both_diff

Reasons:

< [0] func_a_have # Only lhs has this symbol
> [0] func_b_have # Only rhs has this symbol
< [1] func_both_diff # Both have this symbol but symbol signature is different
> [1] func_both_diff # same as previous
< [3] func_const_diff # Both have this symbol but symbol signature is different
> [3] func_const_diff # Same as previous
< [0] var_a_have # Only lhs has this symbol
> [0] var_b_have # Only rhs has this symbol
< [2] var_both_diff # Both have this symbol but symbol signature is different
> [2] var_both_diff # Same as previous