libkernaux

Auxiliary library for kernel development.

Topic on OSDev.org forum.

Table of contents

• Overview
• Table of contents
• API
  • Headers
  • Definitions
  • Global variables
• Configuration
  • Non-default options
  • Default options
• Tips
  • Installation
  • Development
  • Cross

API

Headers

We use semantic versioning for stable APIs. Stable APIs may only change when major version number is increased (or minor while major is zero). Work-in-progress APIs can change at any time.

• Basic features
  • Feature macros (work in progress)
  • Runtime environment (non-breaking since 0.7.0)
  • Macros (non-breaking since 0.6.0)
  • Stack trace (planned)
• Algorithms
  • Page Frame Allocator (work in progress)
• Data formats
  • MBR (work in progress)
• libc replacement (work in progress)
  • ctype.h
  • errno.h
  • inttypes.h
  • setjmp.h
  • stdlib.h
  • string.h
  • sys/types.h
• Architecture-specific code (work in progress)
  • Declarations
  • Functions

Definitions

#define the following C preprocessor macros before including <kernaux.h> and <kernaux/*.h> files. They have effect on your code, not the library code.

• KERNAUX_ACCESS_PRIVATE - disable access modifier "private". Don't do this!
• KERNAUX_ACCESS_PROTECTED - disable access modifier "protected". Only do this in a file where you implement an inherited type.
• KERNAUX_BITFIELDS - enable bitfields in packed structs. It doesn't follow the C standard and may be incompatible with some compilers.

Global variables

// in <kernaux/runtime.h>
void (*kernaux_assert_cb)(const char *file, int line, const char *msg)

Assertion callback. It's better to always set it to some function which always interrupts the execution, even when assertions are disabled. It may for example call abort() in hosted environment, raise an exception in Ruby, panic in Rust or power off the machine in freestanding environment. It may also log the error location and message.

Configuration

Because this library has no external dependencies, we use autoconf features to control behavior of the library, and packages to choose it's components. Configuration options also follow the semantic versioning scheme and are split into stable and work-in-progress ones. Here we cover only stable options.

Non-default options

Features

• --enable-checks - enable usual tests
• --enable-checks-all - enable all checks
• --enable-checks-cppcheck - enable cppcheck Jinja2
• --enable-pkg-config[=PATH] - install pkg-config files [PATH='${libdir}/pkgconfig']

Packages

• --with-libc - provides the replacement for some standard C functions. Useful in freestanding environment, where no libc is present.

Default options

Features

• --(enable|disable)-assert - assertions
• --(enable|disable)-float - floating-point arithmetic
• --(enable|disable)-werror - fail on warning (CFLAGS+='-Werror')

Packages

All packages are included by default. To exclude all packages except those explicitly included, use --without-all.

• --with[out]-arch-all - all architectures
• --with[out]-arch-i386 - architecture i386
• --with[out]-arch-riscv64 - architecture riscv64
• --with[out]-arch-x86-64 - architecture x86-64
• --with[out]-asm - kernel assembler helpers

Tips

Installation

./autogen.sh # if present
./configure
make
sudo make install
sudo ldconfig # on GNU/Linux

This is just a usual library. You can use most of it's APIs in hosted environment.

Development

./autogen.sh # if present
./configure --enable-checks # or --enable-checks-all, but see prerequisites
make

You can test with make check.

See also

• GitHub Actions for GNU/Linux build environment
• Cirrus CI for FreeBSD build environment
• sourcehut CI for OpenBSD build environment

Cross

Create configuration script with ./autogen.sh (if present).

Let's assume that your target triplet is i386-elf. Configure with cross-compiler in $PATH to make without it in $PATH:

./configure \
  --host='i386-elf' \
  --disable-shared \
  --enable-freestanding \
  --with-libc \
  CC="$(which i386-elf-gcc)"

The variables include AR, AS, CC, CCAS, LD, NM, OBJDUMP, RANLIB, STRIP. See the generated config.log for more information.

To install into specific directory use full path: DESTDIR="$(pwd)/dest" make install instead of DESTDIR=dest make install.

Check if compilation targets i386: objdump -d src/asm/i386.o. It should output something like this:

src/asm/i386.o:     file format elf32-i386


Disassembly of section .text:

00000000 <kernaux_asm_i386_read_cr0>:
   0:   0f 20 c0              mov    %cr0,%eax
   3:   c3                    ret

00000004 <kernaux_asm_i386_read_cr4>:
   4:   0f 20 e0              mov    %cr4,%eax
   7:   c3                    ret

00000008 <kernaux_asm_i386_write_cr0>:
   8:   8b 44 24 04           mov    0x4(%esp),%eax
   c:   0f 22 c0              mov    %eax,%cr0
   f:   c3                    ret

00000010 <kernaux_asm_i386_write_cr3>:
  10:   8b 44 24 04           mov    0x4(%esp),%eax
  14:   0f 22 d8              mov    %eax,%cr3
  17:   c3                    ret

00000018 <kernaux_asm_i386_write_cr4>:
  18:   8b 44 24 04           mov    0x4(%esp),%eax
  1c:   0f 22 e0              mov    %eax,%cr4
  1f:   c3                    ret