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 can only change when major version number is increased (or minor while major is zero). Work-in-progress APIs can change at any time.

• Runtime environment
  • Feature macros (work in progress)
  • Assertions (non-breaking since 0.4.0)
    • Assert
    • Panic
  • Stack trace (planned)
  • Input/output (work in progress)
  • Architecture-specific code (work in progress)
    • Declarations
    • Functions
• Device drivers (for debugging only)
  • Serial console (work in progress)
  • Framebuffer (planned)
  • USB (planned)
• Algorithms
  • Simple command line parser (non-breaking since 0.2.0)
    • Example
  • Page Frame Allocator (work in progress)
    • Example
• Data formats
  • ELF (work in progress)
  • Master Boot Record (work in progress)
  • Multiboot 2 (GRUB 2) (work in progress)
  • Stivale 2 (Limine) (planned)
• Utilities
  • Measurement units utils (work in progress)
    • To human
  • Memory map (non-breaking since 0.4.0)
    • Example
  • printf format parser (work in progress)
    • Code from https://github.com/mpaland/printf. Thank you!
    • Example
• Usual functions
  • itoa/ftoa replacement (non-breaking since 0.4.0)
    • Example
  • printf replacement (non-breaking since 0.4.0)
    • Code from https://github.com/mpaland/printf. Thank you!
    • fprintf
    • vfprintf
    • snprintf
    • vsnprintf
• libc replacement (work in progress)
  • ctype.h
  • inttypes.h
  • setjmp.h
  • stdlib.h
  • string.h
  • sys/types.h

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_DEBUG - enable assertions

Global variables

// in <kernaux/assert.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 debugging is 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-tests - enable usual tests and examples
• --enable-tests-all - enable all tests
• --enable-tests-python - enable tests that require Python 3 with YAML and Jinja2

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)-debug - debugging
• --(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]-cmdline - command line parser
• --with[out]-io - input/output
• --with[out]-memmap - memory map
• --with[out]-ntoa - itoa/ftoa
• --with[out]-printf - printf

Tips

Installation

./autogen.sh # if present
./configure
make
sudo make install

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

Development

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

You can test with make check.

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' \
  --enable-freestanding \
  --with-libc \
  AR="$(which i386-elf-ar)" \
  CC="$(which i386-elf-gcc)" \
  RANLIB="$(which i386-elf-ranlib)"

You can see the following messages. It's a bug in autoconf, just ignore it.

checking for _Bool... no
checking stdarg.h usability... no
checking stdarg.h presence... yes
configure: WARNING: stdarg.h: present but cannot be compiled
configure: WARNING: stdarg.h:     check for missing prerequisite headers?
configure: WARNING: stdarg.h: see the Autoconf documentation
configure: WARNING: stdarg.h:     section "Present But Cannot Be Compiled"
configure: WARNING: stdarg.h: proceeding with the compiler's result
configure: WARNING:     ## ---------------------------------------------------------- ##
configure: WARNING:     ## Report this to https://github.com/tailix/libkernaux/issues ##
configure: WARNING:     ## ---------------------------------------------------------- ##
checking for stdarg.h... no
checking stddef.h usability... no
checking stddef.h presence... yes
configure: WARNING: stddef.h: present but cannot be compiled
configure: WARNING: stddef.h:     check for missing prerequisite headers?
configure: WARNING: stddef.h: see the Autoconf documentation
configure: WARNING: stddef.h:     section "Present But Cannot Be Compiled"
configure: WARNING: stddef.h: proceeding with the compiler's result
configure: WARNING:     ## ---------------------------------------------------------- ##
configure: WARNING:     ## Report this to https://github.com/tailix/libkernaux/issues ##
configure: WARNING:     ## ---------------------------------------------------------- ##
checking for stddef.h... no

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