frostbyte v2.4.1

Release notes for frostbyte v2.4.1:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Bug fixes

• Security fix: Hitting enter on shell prompt after pushing stopped process waiting for key input to background dumps entire system key buffer on the console
• Signals causing spurious syscall wake-ups resulting in unexpected program behavior
• Stopped process waiting on keyboard input takes premature control of key buffer
• Error (-1) returned by waitpid syscall not handled by shell
• Job control commands fg, bg cause fatal system exception (ESR value: 0x96000004) on raspberry pi 4
• Stopping a process with Ctrl-Z prints garbage characters after process name in console on raspberry pi 4

Improvements

• Optimize process scheduler list traversal algorithm, improving performance
• Issue key combination (Ctrl-C, Ctrl-Z) generated signals from parent shell rather than current process
• Remove redundant code and optimize kernel system call implementations
• Makefile improvements and comment corrections

Open Issues

#2

Full Changelog: v2.4.0...v2.4.1

frostbyte v2.4.0

Release notes for frostbyte v2.4.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Board support for raspberry pi 4
• New make variable BOARD and segregation of output artifacts based on selected target
• Boot time kernel logs and updated welcome banner
• New option of machine hardware in uname command

Improvements

• Generic FAT16 disk image under boot, modifications made under build preventing changes to disk image on every build
• Reduce memory writes to improve performance
• Copy only required segments of a binary instead of whole page while forking to improve performance
• Optimize stack and heap size to improve performance and memory usage
• Improve shutdown logs
• Improve comments in code
• Prune readme to make it more concise and less pompous

Open Issues

#2

Full Changelog: v2.3.0...v2.4.0

frostbyte v2.3.0

Release notes for frostbyte v2.3.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Process environment with variable name and value pairs, exportable to child processes
• Shell commands (export, env and unset) to monitor and manage process environment
• Enable echo command to evaluate environment variables when preceded by $
• Capability of evaluating nested environment variables in echo, export and unset commands
• Login processes sets universal USER environment variable for shell and its children to identify current user
• Segregation and fixed quota for process stack and heap from the total allocated memory for the process
• Extended userspace virtual address space mapping for process environment
• Implementation of hash map data structure and function algorithms in the kernel

API updates

• Added find() library function to find the index of first occurrence of a character in a given string
• Added POSIX compliant setenv() system call to set an environment variable with given value for the current process and its children
• Added POSIX compliant getenv() system call to get the value of an environment variable by its name
• Added POSIX compliant unsetenv() system call to remove a variable from the current process environment
• Added switchpenv() system call to switch to the parent environment

Caution: This system call serves special purpose within implementation of shell commands like echo and export and should be avoided in regular applications because it irreversibly switches to parent process environment

• Added getfullenv() system call to get a list of all environment variables for current process

Improvements

• Shell deduces current user for its prompt using the USER environment variable instead of -u option used earlier
• Usage of USER environment variable enables propagation of current user to child shell instances instead of having placeholder string "user" for all shell instance prompts spawned from the main shell
• Improve structure and error handling of userspace virtual memory setup and copy kernel functions
• Save process arguments to heap instead of the stack to prevent encroachment of stack space
• Accommodate process page table, kernel stack and heap within the same 2M page for efficiency
• Process table slot cleared before reallocation to prevent corruption due to residual data
• Rectify usage notation for mandatory options/arguments

Bug fixes

• Kernel macros (container_of and offset_of) inaccessible when used with standard headers with missing definitions
• printf() function crashes when string pointer is NULL for %s format specifier
• printf() function gives erratic output when supplied empty string against %s format specifier

frostbyte v2.2.1

Release notes for frostbyte v2.2.1:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Bug fixes

• Pressing Ctrl+C does not provide feedback on shell and takes effect only after pressing Enter key
• Pressing Ctrl+C consecutively kills the shell, logs out in case of main shell (PID 2)
• Ctrl+C does not abort currently typed command and does not renew the prompt

frostbyte v2.2.0

Release notes for frostbyte v2.2.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Job monitoring and control with jobs, fg and bg commands
• Stop and resume processes with SIGTSTP, SIGSTOP and SIGCONT signals
• Ctrl+Z to stop foreground process on shell and create a job

API updates

• Added to_lower() library function to convert a character to lowercase
• Added sort() library function to sort an array of integers in ascending order
• get_proc_data() system call uses an additional argument to fetch job specification of a given process
• Added setjobctl() system call to set job control request for a given job specification
• Added getjpid() system call to get PID of a job specification only if it belongs to current shell session

Improvements

• Optimize key buffer management and notifications for long key sequences and special characters
• Improvements to kernel kill functionality with addition of process parameter
• Improved and optimized process control kernel methods for wait, exit and parent switching
• Process mode checked on waking up as a background process waiting for keyboard input
• Prevent dumping of residual characters from previous foreground process by flushing key buffer
• Additional methods for finding and getting the last element in a linked list
• Set up build system for debug and release build types

Bug fixes

• Key buffer pointer gets corrupted on resuming a stopped process
• PID of stopped process not returned by the wait system call
• Shell used PID returned by fork() instead of return value from wait() to check status of process being waited for
• Zombies hijacked by init during exit even when parent waiting for them
• Termination and suspension signal handlers do not remove a process from waitlist
• SIGKILL handler does not kill children
• SIGKILL handler does not unblock the parent if it is waiting

frostbyte v2.1.0

Release notes for frostbyte v2.1.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Cursor movement on shell with arrow keys
• Character insertion and deletion by moving cursor to edit typed commands and arguments
• Raw input processing for scanf() and login password prompt for all key sequences
• Session and system wide process information with ps command

API updates

• sleep() system call renamed to msleep() to reflect it's nature of sleeping at millisecond intervals than seconds and prevent prototype declaration conflict of sleep() function in C standard header files
• get_active_procs() system call uses an additional argument to determine process snapshot request type

Improvements

• Improved command line option parsing logic making command arguments sequence and position agnostic
• Command arguments can be stitched together with a single -. For example, ps -e -f and ps -ef are both valid and identical
• Improved usage output format on typing <command> -h for applicable commands

Bug fixes

• Zombies not cleaned up on user log out, persist in next user session
• Background processes spawned from the shell with & turn into zombies after normal exit
• Process exit status not tracked on delivering a SIGKILL

frostbyte v2.0.1

Release notes for frostbyte v2.0.1:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Updates

• LICENSE update to GPL v3
• LICENSE present in source tree and notice attached to all source files

Bug fixes

• Issue #1 fixed - Serial console unresponsive on pressing arrow keys
• Login accepted if only the starting slice of the username entered matched with the name entry in passwd file

Open issues

frostbyte v2.0.0

Release notes for frostbyte v2.0.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Login shell/prompt backed by passwd file on FAT16 disk
• Standard passwd file format with password-less configuration
• Full format ps output with command line arguments for every process using the -f option
• Enable init process (PID 1) to wait for own children and processes orphaned by exiting parents
• Respawn login shell on exit of main shell
• POSIX compliant exit and echo commands

API updates

• wait() system call can query child exit status using standard macros in sys/wait.h by passing the returned status
• waitpid() system call can wait for multiple children with -1 as value of pid argument and provide options to configure wait execution
• exit() system call accepts status argument and also passes the return value from main() to the kernel as exit status
• kill() system call accepts pid argument as 0 for sending signals to group and -1 for system wide signalling as per POSIX standard
• get_proc_data() system call has new argument to accept process command line arguments. Used by the ps full format command
• Added POSIX compliant waitpid() system call
• Added get_pstatus() system call to enable a process to query the parent processes current status

Improvements

• Shutdown logs printed in correct sequence as and when they are terminated rather than when the signal is delivered
• Enable wait() function to process all child processes
• Update shutdown message to make it useful than entertaining
• Restructure Makefile to supply toolchain include paths to kernel and userspace programs

Bug fixes

• Nested shell executions corrupt keyboard buffer read position pointers
• Signal handler gets reset to default with SIG_IGN argument to signal() system call
• Default handler not set for SIGABRT
• Zombies not cleaned on exiting from nested shell
• exit command not fetching last command's status when executed without options
• tail pointer and list termination not handled correctly

Open issues

#1

frostbyte v1.0.0

Release notes for frostbyte v1.0.0:

Note: Release notes for current version are created as a delta against previous version's release notes i.e. features, improvements and bug fixes from previous releases will be present in the current release by default unless mentioned otherwise

Features

• Kernel at EL1 and user programs at EL0
• Synchronous and asynchronous exception handling
• Interrupt handling and interrupt vector table
• Timer interrupt based FIFO scheduling
• Paging and virtual memory management
• FAT16 filesystem support and VFS
• Interactive shell on serial console
• POSIX compliant system calls and commands
• POSIX signal handling framework
• Custom standard library functions
• Custom programs with command-line arguments and user input
• Foreground and background process management

Improvements

Bug fixes

Open issues

#1