assignments: Introduce mini-libc assignment

Mini-libc is a minimalistic standard C library (libc) implementation. It
is meant to be used as a complete replacement for the system libc (glibc
in Linux). This is why test programs are built with `-nostinc`,
`-nostlib`, `-fno-builtin` options.

The actual library source code is part of the `libc/` directory. It is
to be compiled as a static library in the `libc.a` file.

A set of sample use cases, as C source files, are stored in the
`samples/` directory.

Tests are in the `tests/` directory, both as source code and shell
scripts.

The aim is to have a minimally functional libc with features such as:

- string management
- very basic memory support
- POSIX file I/O (i.e. `open()`, `read()`, `write()`)
- basic printing (`puts()`)
- sleep functions

Signed-off-by: Razvan Deaconescu <razvan.deaconescu@upb.ro>
Signed-off-by: Ruxandra Grigorie <ruxi.grigorie@gmail.com>
Signed-off-by: Teodor Dutu <teodor.dutu@gmail.com>
Signed-off-by: Adrian Șendroiu <molecula2788@gmail.com>
Signed-off-by: Gabriel Mocanu <gabi.mocanu98@gmail.com>
Signed-off-by: Alexandru Apostolescu <alexx.apostolescu@gmail.com>
Signed-off-by: Alex-Costin Puflene <alexpufi22@yahoo.com>
Signed-off-by: Vlad Tiftilov <vlad.tiftilov@yahoo.com>
Signed-off-by: Laurențiu Ursu <laurentiu.ursu2001@gmail.com>
Signed-off-by: Iulia-Silvia Plăiașu <isplaiasu@gmail.com>

content/assignments/mini-libc/README.md

@@ -1 +1,281 @@
-# Mini Libc
+# Mini-libc
+
+## Objectives
+
+- Learn about the structure and functionalities provided by the standard C library
+- Accommodate with the syscall interface in Linux
+- Gain a better understanding of strings and memory management functions
+- Learn how the standard C library provides support for low-level input/output operations
+
+## Statement
+
+Build a **minimalistic** [**standard C library**](https://en.wikipedia.org/wiki/C_standard_library) implementation for Linux systems (named **mini-libc**), that can be used as a replacement for the **system libc** ([glibc](https://www.gnu.org/software/libc/) in Linux).
+The goal is to have a minimally functional libc with features such as string management, basic memory support and POSIX file I/O.
+
+The implementation of mini-libc will be **freestanding**, i.e. it will not use any outside library calls.
+It will be implemented on top of the system call interface provided by Linux on an `x86_64` architecture.
+Any function you require, that is typically part of libc, you will have to implement.
+You can reuse functions that you implement in other parts of the mini-libc.
+
+In case you are using a macOS device with ARM64 / Aarch64, you will have to install an `x86_64` virtual machine.
+
+## Support Code
+
+The support code consists of three directories:
+
+- `libc/` is the skeleton mini-libc implementation.
+  You will have to implement missing parts marked as `TODO` items.
+
+- `samples/` stores use cases and tests of mini-libc.
+
+- `tests/` are states used to validate (and grade) the assignment.
+
+System call invocation is done via the `syscall()` function defined in `libc/syscall.c`.
+That itself makes a call to the architecture-specific call in `libc/internal/arch/x86_64/syscall_arch.h`;
+hence the dependency on the `x86_64` architecture.
+
+### API and Implementation Tasks
+
+The application programming interface (API) of the C standard library is declared in a number of header files.
+Each header file contains one or more function declarations, data type definitions and macros.
+For your minimal implementation, the following header files are of interest:
+
+- `<string.h>`: defines string-handling functions
+
+  For this assignment, you will have to implement the following functions: `strcpy()`, `strcat()`, `strlen()`, `strncpy()`, `strncat()`, `strcmp()`, `strncmp()`, `strstr()`, `strrstr()`, `memcpy()`, `memset()`, `memmove()`, `memcmp()`.
+
+- `<stdio.h>`: defines printing and I/O functions
+
+  For this assignment, you will have to implement `puts()`.
+
+- `<unistd.h>`, `<sys/fcntl.h>` and `<sys/stat.h>`: define I/O primitives
+
+  For this assignment, you will have to implement the following functions: `open()`, `close()`, `lseek()`, `stat()`, `fstat()`, `truncate()`, `ftruncate()`.
+
+  You will also have to implement the `nanosleep()` and `sleep()` functions.
+
+- `<stdlib.h`> and `<sys/mman.h>` define memory allocation functions
+
+  For this assignment, you will have to implement the following functions: `malloc()`, `free()`, `calloc()`, `realloc()`, `realloc_array()`, `mmap()`, `mremap()`, `munmap()`.
+
+  For managing memory areas, a basic list structure is provided in `include/internal/mm/mem_list.h` and `mm/mem_list.c`.
+
+- `<errno.h>` and `errno.c`: declare and define the integer variable `errno`, which is set by system calls and some library functions in the event of an error to indicate what went wrong.
+
+Some tests do not build.
+This is intentional.
+You will have to add the missing features to make those tests compile, that is
+
+- the `time.h` header
+- the declaration and the implementation of `puts()`
+- the declaration and the implementation of `nanosleep()` and `sleep()`
+- the update of the libc `Makefile` to build the source code files implementing `puts()`, `nanosleep()` and `sleep()`
+
+  :exclamation::exclamation: **Pay attention** to which functions have to modify the `errno` variable.
+
+### Building mini-libc
+
+To build mini-libc, run `make` in the `libc/` directory:
+
+```console
+student@so:~/.../content/assignments/mini-libc$ cd libc/
+
+student@so:~/.../assignments/mini-libc/libc$ make
+```
+
+To build samples, enter the `samples` directory and run `make`:
+
+```console
+student@so:~/.../content/assignments/mini-libc$ cd samples/
+
+student@so:~/.../assignments/mini-libc/samples$ make
+```
+
+## Testing and Grading
+
+The testing is automated.
+Tests are located in the `tests/` directory.
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ ls -F
+graded_test.c       memory/             test_io.c                      test_malloc_free.sh*        test_mmap_munmap.sh*      test_multiple_malloc_free.sh*  test_sleep.sh*
+graded_test.h       process/            test_io_file_create.sh*        test_malloc_perm_notok.sh*  test_mmap_perm_none.sh*   test_multiple_malloc.sh*       test_stat.sh*
+graded_test.inc.sh  run_all_tests.sh*   test_io_file_delete.sh*        test_malloc_perm_ok.sh*     test_mmap_perm_notok.sh*  test_nanosleep.sh*             test_string.c
+io/                 test_fstat.sh*      test_lseek.sh*                 test_malloc.sh*             test_mmap_perm_ok.sh*     test_open_close.sh*            test_truncate.sh*
+Makefile            test_ftruncate.sh*  test_malloc_free_sequence.sh*  test_memory.c               test_mmap.sh*             test_puts.sh*
+```
+
+To run the checker and everything else required, use the `make check` command in the `tests/` directory:
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ make check
+make[1]: Entering directory '...'
+rm -f *~
+[...]
+test_mmap_perm_ok                ........................ failed ...  0
+test_mmap_perm_notok             ........................ failed ...  0
+test_mmap_perm_none              ........................ failed ...  0
+
+Grade                            .................................. 0.06
+```
+
+For starters, tests will fail.
+Some tests don't fail because the missing implementation equates to the bad behavior being tested not happening.
+That's why you get the `0.06` grade.
+
+Each test is worth a number of points.
+The total number of points is `900`.
+The maximum grade is obtained by dividing the number of points to `100`, for a maximum grade of `9.00`.
+
+A successful run will show the output:
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ make check
+[...]
+test_strcpy                      ........................ passed ...   9
+test_strcpy_append               ........................ passed ...   9
+test_strncpy                     ........................ passed ...   9
+test_strncpy_cut                 ........................ passed ...   9
+test_strcat                      ........................ passed ...   9
+test_strcat_from_zero            ........................ passed ...   9
+test_strcat_multiple             ........................ passed ...   9
+test_strncat                     ........................ passed ...   9
+test_strncat_cut                 ........................ passed ...   9
+test_strcmp_equal                ........................ passed ...   9
+test_strcmp_same_size_less       ........................ passed ...   1
+test_strcmp_same_size_greater    ........................ passed ...   9
+test_strcmp_diff_size_less       ........................ passed ...   1
+test_strcmp_diff_size_greater    ........................ passed ...   9
+test_strncmp_equal_size_equal    ........................ passed ...   9
+test_strncmp_diff_contents_equal ........................ passed ...   9
+test_strncmp_diff_size_equal     ........................ passed ...   9
+test_strchr_exists               ........................ passed ...  11
+test_strchr_exists_twice         ........................ passed ...   9
+test_strchr_not_exists           ........................ passed ...   1
+test_strrchr_exists              ........................ passed ...  11
+test_strrchr_exists_twice        ........................ passed ...   9
+test_strrchr_not_exists          ........................ passed ...   1
+test_strstr_exists               ........................ passed ...  11
+test_strstr_exists_twice         ........................ passed ...   9
+test_strstr_not_exists           ........................ passed ...   1
+test_strrstr_exists              ........................ passed ...  11
+test_strrstr_exists_twice        ........................ passed ...   9
+test_strrstr_not_exists          ........................ passed ...   1
+test_memcpy                      ........................ passed ...  11
+test_memcpy_part                 ........................ passed ...   9
+test_memcmp_equal_size_equal     ........................ passed ...   9
+test_memcmp_diff_contents_equal  ........................ passed ...   9
+test_memcmp_diff_size_equal      ........................ passed ...   9
+test_memset                      ........................ passed ...   9
+test_memset_part                 ........................ passed ...   9
+test_memmove_apart               ........................ passed ...   9
+test_memmove_src_before_dst      ........................ passed ...   9
+test_memmove_src_after_dst       ........................ passed ...   9
+test_open_non_existent_file      ........................ passed ...   8
+test_open_invalid_access_mode    ........................ passed ...   8
+test_open_file_as_directory      ........................ passed ...   8
+test_open_directory_for_writing  ........................ passed ...   8
+test_open_force_invalid_creation ........................ passed ...   8
+test_open_close_existent_file    ........................ passed ...   8
+test_open_close_create_file      ........................ passed ...   8
+test_open_read_write_only_mode   ........................ passed ...   8
+test_open_write_read_only_mode   ........................ passed ...   8
+test_lseek_invalid_fd            ........................ passed ...   8
+test_lseek_invalid_whence        ........................ passed ...   8
+test_lseek_invalid_offset        ........................ passed ...   8
+test_lseek_set                   ........................ passed ...   8
+test_lseek_cur                   ........................ passed ...   8
+test_lseek_end                   ........................ passed ...   8
+test_lseek_combined              ........................ passed ...   8
+test_truncate_read_only_file     ........................ passed ...   8
+test_truncate_invalid_size       ........................ passed ...   8
+test_truncate_directory          ........................ passed ...   8
+test_truncate_non_existent_file  ........................ passed ...   8
+test_truncate_file               ........................ passed ...   8
+test_ftruncate_read_only_file    ........................ passed ...   8
+test_ftruncate_invalid_size      ........................ passed ...   8
+test_ftruncate_directory         ........................ passed ...   8
+test_ftruncate_bad_fd            ........................ passed ...   8
+test_ftruncate_file              ........................ passed ...   8
+test_stat_non_existent_file      ........................ passed ...   8
+test_stat_regular_file           ........................ passed ...   8
+test_fstat_bad_fd                ........................ passed ...   8
+test_fstat_regular_file          ........................ passed ...   8
+test_puts                        ........................ passed ...  15
+test_open_close_create_file      ........................ passed ...  10
+test_open_close_read_byte        ........................ passed ...  10
+test_ftruncate                   ........................ passed ...  10
+test_truncate                    ........................ passed ...  10
+test_fstat                       ........................ passed ...  10
+test_stat                        ........................ passed ...  10
+test_sleep                       ........................ passed ...  20
+test_nanosleep                   ........................ passed ...  20
+test_mmap                        ........................ passed ...   8
+test_mmap_bad_fd                 ........................ passed ...   8
+test_mmap_bad_flags              ........................ passed ...   8
+test_mremap                      ........................ passed ...   8
+test_malloc                      ........................ passed ...   8
+test_malloc_two                  ........................ passed ...   8
+test_malloc_access               ........................ passed ...   8
+test_malloc_memset               ........................ passed ...   8
+test_malloc_memcpy               ........................ passed ...   8
+test_calloc                      ........................ passed ...   8
+test_realloc                     ........................ passed ...   8
+test_realloc_access              ........................ passed ...   8
+test_realloc_memset              ........................ passed ...   8
+test_realloc_array               ........................ passed ...   8
+test_malloc                      ........................ passed ...  10
+test_multiple_malloc             ........................ passed ...  10
+test_malloc_free                 ........................ passed ...  10
+test_multiple_malloc_free        ........................ passed ...  10
+test_malloc_free_sequence        ........................ passed ...  10
+test_malloc_perm_ok              ........................ passed ...  10
+test_malloc_perm_notok           ........................ passed ...  10
+test_mmap                        ........................ passed ...  10
+test_mmap_munmap                 ........................ passed ...  10
+test_mmap_perm_ok                ........................ passed ...  10
+test_mmap_perm_notok             ........................ passed ...  10
+test_mmap_perm_none              ........................ passed ...  10
+
+Total                            .................................. 9.00
+```
+
+### Behind the Scenes
+
+For a fine grained approach, build tests and ignore errors (due to missing source code and header files) by using:
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ make -i
+```
+
+Then run the tests, either individually via executable files and scripts:
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ ./test_lseek.sh
+test_lseek                       ........................ passed ...  10
+
+student@so:~/.../assignments/mini-libc/tests$ ./test_memory
+test_mmap                        ........................ passed ...   8
+test_mmap_bad_fd                 ........................ passed ...   8
+[...]
+```
+
+Or run them all via the `run_all_tests.sh` script:
+
+```console
+student@so:~/.../assignments/mini-libc/tests$ ./run_all_tests.sh
+test_strcpy                      ........................ passed ...   9
+test_strcpy_append               ........................ passed ...   9
+test_strncpy                     ........................ passed ...   9
+[...]
+```
+
+## Resources
+
+- [GNU libc manual](https://www.gnu.org/software/libc/manual/html_mono/libc.html)
+
+- [musl implementation of the standard C library for Linux-based systems](https://elixir.bootlin.com/musl/latest/source)
+
+- Syscall interface in Linux - [Linux man pages online](https://man7.org/linux/man-pages/index.html)
+
+- [glibc implementation of the standard C library for Linux-based systems](https://elixir.bootlin.com/glibc/latest/source)

content/assignments/mini-libc/libc/Makefile

@@ -0,0 +1,36 @@
+NASM = nasm
+CPPFLAGS = -nostdinc -Iinclude
+CFLAGS = -Wall -Wextra -fno-PIC -fno-stack-protector -fno-builtin
+# Remove the line below to disable debugging support.
+CFLAGS += -g -O0
+
+.PHONY: all clean
+
+SRCS = syscall.c \
+       process/exit.c \
+       mm/malloc.c mm/mmap.c mm/mem_list.c \
+       string/string.c \
+       stat/fstatat.c stat/fstat.c stat/stat.c \
+       io/open.c io/close.c io/read_write.c \
+       io/lseek.c io/truncate.c io/ftruncate.c \
+       errno.c \
+       crt/__libc_start_main.c
+
+# TODO: Add sleep.c and puts.c dependency.
+
+OBJS = $(patsubst %.c,%.o,$(SRCS))
+
+all: libc.a
+
+libc.a: $(OBJS) crt/start.o
+	$(AR) -rc $@ $^
+
+$(OBJS): %.o:%.c
+
+crt/start.o: crt/start.asm
+	$(NASM) -f elf64 -o $@ $<
+
+clean:
+	-rm -f *~
+	-rm -f $(OBJS) crt/start.o
+	-rm -f libc.a

content/assignments/mini-libc/libc/crt/__libc_start_main.c

@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include <internal/types.h>
+#include <internal/mm/mem_list.h>
+
+static void init(void)
+{
+	mem_list_init();
+}
+
+static void cleanup(void)
+{
+	mem_list_cleanup();
+}
+
+int __libc_start_main(int (*main_fn)(void))
+{
+	int exit_code;
+
+	init();
+	exit_code = main_fn();
+	cleanup();
+
+	return exit_code;
+}

content/assignments/mini-libc/libc/crt/start.asm

@@ -0,0 +1,16 @@
+extern main
+extern exit
+extern __libc_start_main
+
+section .text
+
+global _start
+
+_start:
+    mov rdi, main
+    call __libc_start_main
+
+    mov rdi, rax
+    call exit
+
+    hlt

content/assignments/mini-libc/libc/errno.c

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include <errno.h>
+
+int errno;