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0x05-libasm

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(376) 0x05. x86 Assembly - libASM

Specializations > System programming & Algorithm > Linux Programming

Project author

Alexandre Gautier

Assignment dates

02-01-2021 to 02-12-2021

Description

Introduction to x86 assembly: Intel vs AT&T, flag registers, stack frames, function and system calls.

Requirements

  • Allowed Functions and System Calls Unless specified otherwise, you are NOT allowed to do any call or make any system call. It means you’re not allowed to use either the call nor the syscall instructions.
  • ASM programs and functions expected to be compiled with NASM version 2.10.09 using the flags -f elf64

Provided file(s)

Mandatory Tasks

✅ 0. strlen

Write a copycat of the function strlen(3), in x86-64 Assembly

  • Prototype when used in C: size_t asm_strlen(const char *str);

File(s): 0-strlen.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 0-main.o 0-main.c
$ nasm -f elf64 -o 0-strlen.o 0-strlen.asm
$ gcc -o 0-strlen 0-main.o 0-strlen.o

✅ 1. strcmp

Write a copycat of the function strcmp(3), in x86-64 Assembly

  • Prototype when used in C: int asm_strcmp(const char *s1, const char *s2);

File(s): 1-strcmp.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 1-main.o 1-main.c
$ nasm -f elf64 -o 1-strcmp.o 1-strcmp.asm
$ gcc -o 1-strcmp 1-main.o 1-strcmp.o

✅ 2. strncmp

Write a copycat of the function strncmp(3), in x86-64 Assembly

  • Prototype when used in C: int asm_strncmp(const char *s1, const char *s2, size_t n);

File(s): 2-strncmp.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 2-main.o 2-main.c
$ nasm -f elf64 -o 2-strncmp.o 2-strncmp.asm
$ gcc -o 2-strncmp 2-main.o 2-strncmp.o

✅ 3. strchr

Write a copycat of the function strchr(3), in x86-64 Assembly

  • Prototype when used in C: char *asm_strchr(const char *s, int c);

File(s): 3-strchr.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 3-main.o 3-main.c
$ nasm -f elf64 -o 3-strchr.o 3-strchr.asm
$ gcc -o 3-strchr 3-main.o 3-strchr.o

✅ 4. strstr

Write a copycat of the function strstr(3), in x86-64 Assembly

  • Prototype when used in C: char *asm_strstr(const char *haystack, const char *needle);

File(s): 4-strstr.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 4-main.o 4-main.c
$ nasm -f elf64 -o 4-strstr.o 4-strstr.asm
$ gcc -o 4-strstr 4-main.o 4-strstr.o

✅ 5. memcpy

Write a copycat of the function memcpy(3), in x86-64 Assembly

  • Prototype when used in C: void *asm_memcpy(void *dest, const void *src, size_t n);

File(s): 5-memcpy.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 5-main.o 5-main.c
$ nasm -f elf64 -o 5-memcpy.o 5-memcpy.asm
$ gcc -o 5-memcpy 5-main.o 5-memcpy.o

✅ 6. putc

Write a function that prints a single character on the standard output, in x86-64 Assembly

  • Prototype when used in C: size_t asm_putc(int c);
  • Where c holds the character to be printed
  • Your function must return the total number of bytes written on the standard output
  • For this task, you are allowed to use the syscall instruction only once in your file

File(s): 6-putc.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 6-main.o 6-main.c
$ nasm -f elf64 -o 6-putc.o 6-putc.asm
$ gcc -o 6-putc 6-main.o 6-putc.o

✅ 7. puts

Write a function that prints a string of characters on the standard output, in x86-64 Assembly

  • Prototype when used in C: size_t asm_puts(const char *str);
  • Where str holds the string to be printed
  • Your function must return the total number of bytes written on the standard output
  • You are not allowed to use any sort of jump
  • Your file 0-strlen.asm will be compiled as well, you are allowed to call it once in your file
  • For this task, you are allowed to use the syscall instruction only once in your file

File(s): 7-puts.asm 0-strlen.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 7-main.o 7-main.c
$ nasm -f elf64 -o 7-puts.o 7-puts.asm
$ nasm -f elf64 -o 0-strlen.o 0-strlen.asm
$ gcc -o 7-puts 7-main.o 7-puts.o 0-strlen.o

✅ 8. strcasecmp

Write a copycat of the function strcasecmp(3), in x86-64 Assembly

  • Prototype when used in C: int asm_strcasecmp(const char *s1, const char *s2);

File(s): 8-strcasecmp.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 8-main.o 8-main.c
$ nasm -f elf64 -o 8-strcasecmp.o 8-strcasecmp.asm
$ gcc -o 8-strcasecmp 8-main.o 8-strcasecmp.o

✅ 9. strncasecmp

Write a copycat of the function strncasecmp(3), in x86-64 Assembly

  • Prototype when used in C: int asm_strncasecmp(const char *s1, const char *s2, size_t n);

File(s): 9-strncasecmp.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 9-main.o 9-main.c
$ nasm -f elf64 -o 9-strncasecmp.o 9-strncasecmp.asm
$ gcc -o 9-strncasecmp 9-main.o 9-strncasecmp.o

✅ 10. strspn

Write a copycat of the function strspn(3), in x86-64 Assembly

  • Prototype when used in C: size_t asm_strspn(const char *s, const char *accept);

File(s): 10-strspn.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 10-main.o 10-main.c
$ nasm -f elf64 -o 10-strspn.o 10-strspn.asm
$ gcc -o 10-strspn 10-main.o 10-strspn.o

✅ 11. strcspn

Write a copycat of the function strcspn(3), in x86-64 Assembly

  • Prototype when used in C: size_t asm_strcspn(const char *s, const char *reject);

File(s): 11-strcspn.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 11-main.o 11-main.c
$ nasm -f elf64 -o 11-strcspn.o 11-strcspn.asm
$ gcc -o 11-strcspn 11-main.o 11-strcspn.o

✅ 12. strpbrk

Write a copycat of the function strpbrk(3), in x86-64 Assembly

  • Prototype when used in C: char *asm_strpbrk(const char *s, const char *accept);

File(s): 12-strpbrk.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 12-main.o 12-main.c
$ nasm -f elf64 -o 12-strpbrk.o 12-strpbrk.asm
$ gcc -o 12-strpbrk 12-main.o 12-strpbrk.o

Advanced Tasks

✅ 13. puti

Write a function that prints a signed integer on the standard output, in x86-64 Assembly

  • Prototype when used in C: size_t asm_puti(int n);
  • Where n holds the integer to be printed
  • Your function must return the total number of bytes written on the standard output
  • Your file 6-putc.asm will be compiled as well
  • You are allowed to use the instruction call up to three times in your file

File(s): 100-puti.asm 6-putc.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 100-main.o 100-main.c
$ nasm -f elf64 -o 100-puti.o 100-puti.asm
$ nasm -f elf64 -o 6-putc.o 6-putc.asm
$ gcc -o 100-puti 100-main.o 100-puti.o 6-putc.o

✅ 14. puti_base

Write a function that prints a signed integer in a given base on the standard output, in x86-64 Assembly

  • Prototype when used in C: size_t asm_puti_base(int n, const char *base);
  • Where n holds the integer to be printed
  • And base points to a string representing the base used to print n
  • Your function must return the total number of bytes written on the standard output
  • Your files 6-putc.asm and 0-strlen.asm will be compiled as well
  • You are allowed to use the instruction call up to four times in your file

File(s): 101-puti_base.asm 6-putc.asm 0-strlen.asm
Compiled:

$ gcc -Wall -Wextra -Werror -pedantic -g3 -c -o 101-main.o 101-main.c
$ nasm -f elf64 -o 101-puti_base.o 101-puti_base.asm
$ nasm -f elf64 -o 6-putc.o 6-putc.asm
$ nasm -f elf64 -o 0-strlen.o 0-strlen.asm
$ gcc -o 101-puti_base 101-main.o 101-puti_base.o 6-putc.o 0-strlen.o

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