stack/intro: Lab 8 - Stiva

chapters/stack/intro/drills/tasks/gcd/README.md

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+# GCD - Greatest Common Divisor
+
+Open `gcd.asm` and run the program.
+The code calculates the greatest common divisor (GCD) of two numbers given as parameters using the `eax` and `edx` registers, and then stores the calculated value back in the `eax` register.
+
+1. Make the necessary modifications so that the error message - `Segmentation fault (core dumped)` - no longer appears.
+1. Within the `print` label, display the result in the following format:
+
+```c
+gcd(49,28)=7
+```
+
+If you're having difficulties solving this exercise, go through [this](../../../reading/README.md) reading material

chapters/stack/intro/drills/tasks/gcd/solution/.gitignore

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+gcd

chapters/stack/intro/drills/tasks/gcd/solution/Makefile

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+../support/Makefile

chapters/stack/intro/drills/tasks/gcd/solution/gcd.asm

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+;  SPDX-License-Identifier: BSD-3-Clause
+
+%include "../utils/printf32.asm"
+
+section .text
+
+extern printf
+global main
+main:
+    ; Input values (eax, edx) : the 2 numbers to compute the gcd for.
+    mov eax, 49
+    mov edx, 28
+
+    push eax
+    push edx
+
+gcd:
+    neg eax
+    je gcd_end
+
+swap_values:
+    neg eax
+    push eax
+    push edx
+    pop eax
+    pop edx
+
+subtract_values:
+    sub eax,edx
+    jg subtract_values
+    jne swap_values
+
+gcd_end:
+    add eax,edx
+    jne print
+    inc eax
+
+print:
+    pop edx
+    pop ebx
+
+    PRINTF32 `gcd(%d, %d) = %d\n\x0`, ebx, edx, eax  ; eax = greatest common divisor
+
+    xor eax, eax
+    ret

chapters/stack/intro/drills/tasks/gcd/support/.gitignore

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+gcd

chapters/stack/intro/drills/tasks/gcd/support/Makefile

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+AS = nasm
+CC = gcc
+RM = rm
+
+SRCS := $(shell find . -name "*.asm")
+OBJS := $(SRCS:.asm=.o)
+
+UTILSDIR := ../utils/
+
+ASFLAGS ?= -f elf32 -F dwarf -I "$(UTILSDIR)"
+CFLAGS ?= -Wall
+LDFLAGS ?= -m32 -no-pie
+
+TARGET_EXEC = gcd
+
+$(TARGET_EXEC): $(OBJS)
+	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
+
+$(OBJS): $(SRCS)
+	$(AS) $(ASFLAGS) $< -o $@
+
+.PHONY: clean
+
+clean:
+	$(RM) -r *.o $(TARGET_EXEC)

chapters/stack/intro/drills/tasks/gcd/support/gcd.asm

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+%include "printf32.asm"
+
+section .text
+
+extern printf
+global main
+main:
+    ; input values (eax, edx): the 2 numbers to compute the gcd for
+    mov eax, 49
+    mov edx, 28
+
+    push eax
+    push edx
+
+gcd:
+    neg eax
+    je gcd_end
+
+swap_values:
+    neg eax
+    push eax
+    push edx
+    pop eax
+    pop edx
+
+subtract_values:
+    sub eax,edx
+    jg subtract_values
+    jne swap_values
+
+gcd_end:
+    add eax,edx
+    jne print
+    inc eax
+
+print:
+
+    ; TODO 1: solve the 'Segmentation fault!' error
+
+    ; TODO 2: print the result in the form of: "gdc(eax, edx)=7" with PRINTF32 macro
+    ; output value in eax
+
+    xor eax, eax
+    ret

chapters/stack/intro/drills/tasks/gcd/utils/printf32.asm

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+; SPDX-License-Identifier: BSD-3-Clause
+
+;;; macro to use printf with 32bit parameters:
+;;; - 1st parameter MUST be an immediate in backquotes `EAX=%d ECX=%x \n\x0`
+;;;     escape \n and \x0 only work with backquotes
+;;; - rest of parameters MUST be 32bit
+;;; - gen purpose and flags are preserved
+;;; - stack is cleaned
+%macro PRINTF32 1-*
+    pushf
+    pushad
+    jmp     %%endstr
+%%str:       db      %1
+%%endstr:
+%rep  %0 - 1
+%rotate -1
+    push    dword %1
+%endrep
+    push %%str
+    call printf
+    add esp, 4*%0
+    popad
+    popf
+%endmacro

chapters/stack/intro/drills/tasks/local-var/README.md

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+# Local Var
+
+The program `local-var.asm` in the laboratory archive combines two sorted arrays (`array_1` and `array_2`) by placing the resulting array in `array_output` defined in the `.data` section.
+
+Modify the program so that `array_1`, `array_2`, and `array_output` are allocated on the stack.
+The array allocation is done using the `sub` instruction.
+For the copies of arrays `array_1` and `array_2`, you will need to copy their elements from the `.data` section to the stack before using them.
+
+If you're having difficulties solving this exercise, go through [this](../../../reading/README.md) reading material

chapters/stack/intro/drills/tasks/local-var/solution/.gitignore

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+local-var

chapters/stack/intro/drills/tasks/local-var/solution/Makefile

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+../support/Makefile

chapters/stack/intro/drills/tasks/local-var/solution/local-var.asm

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+%include "../utils/printf32.asm"
+
+section .data
+
+%define ARRAY_1_LEN 5
+%define ARRAY_2_LEN 7
+%define ARRAY_OUTPUT_LEN 12
+
+section .data
+array_1 dd 27, 46, 55, 83, 84
+array_2 dd 1, 4, 21, 26, 59, 92, 105
+
+section .text
+
+extern printf
+global main
+
+main:
+    mov ebp, esp
+    sub esp, 4 * ARRAY_1_LEN
+    mov eax, esp
+    mov edx, 0
+array_1_on_stack:
+    mov ecx, [array_1 + 4 * edx]
+    mov [eax], ecx
+    inc edx
+    add eax, 4
+    cmp edx, ARRAY_1_LEN
+    jl array_1_on_stack
+    mov eax, esp
+
+    sub esp, 4 * ARRAY_2_LEN
+    mov ebx, esp
+    mov edx, 0
+array_2_on_stack:
+    mov ecx, [array_2 + 4 * edx]
+    mov [ebx], ecx
+    inc edx
+    add ebx, 4
+    cmp edx, ARRAY_2_LEN
+    jl array_2_on_stack
+    mov ebx, esp
+    sub esp, 4 * ARRAY_OUTPUT_LEN
+    mov ecx, esp
+
+merge_arrays:
+    mov edx, [eax]
+    cmp edx, [ebx]
+    jg array_2_lower
+array_1_lower:
+    mov [ecx], edx  ; The element from array_1 is lower
+    add eax, 4
+    add ecx, 4
+    jmp verify_array_end
+array_2_lower:
+    mov edx, [ebx]
+    mov [ecx], edx  ; The elements of the array_2 is lower
+    add ebx, 4
+    add ecx, 4
+
+verify_array_end:
+    mov edx, ebp
+    cmp eax, edx
+    jge copy_array_2
+    sub edx, 4 * ARRAY_1_LEN
+    cmp ebx, ebp
+    jge copy_array_1
+    jmp merge_arrays
+
+copy_array_1:
+    xor edx, edx
+    mov eax, [eax]
+    mov [ecx], edx
+    add ecx, 4
+    add eax, 4
+    cmp eax, ebp
+    jb copy_array_1
+    jmp print_array
+copy_array_2:
+    xor edx, edx
+    mov edx, [ebx]
+    mov [ecx], edx
+    add ecx, 4
+    add ebx, 4
+    mov edx, ebp
+    sub edx, 4 * ARRAY_1_LEN
+    cmp ebx, edx
+    jb copy_array_2
+
+print_array:
+    PRINTF32 `Array merged:\n\x0`
+    xor eax, eax
+    xor ecx, ecx
+
+print:
+    mov eax, [esp]
+    PRINTF32 `%d \x0`, eax
+    add esp, 4
+    inc ecx
+    cmp ecx, ARRAY_OUTPUT_LEN
+    jb print
+
+    PRINTF32 `\n\x0`
+    xor eax, eax
+    mov esp, ebp
+    ret

chapters/stack/intro/drills/tasks/local-var/support/.gitignore

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+local-var

chapters/stack/intro/drills/tasks/local-var/support/Makefile

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+AS = nasm
+CC = gcc
+RM = rm
+
+SRCS := $(shell find . -name "*.asm")
+OBJS := $(SRCS:.asm=.o)
+
+UTILSDIR := ../utils/
+
+ASFLAGS ?= -f elf32 -F dwarf -I "$(UTILSDIR)"
+CFLAGS ?= -Wall
+LDFLAGS ?= -m32 -no-pie
+
+TARGET_EXEC = local-var
+
+$(TARGET_EXEC): $(OBJS)
+	$(CC) $(CFLAGS) $(LDFLAGS) $< -o $@
+
+$(OBJS): $(SRCS)
+	$(AS) $(ASFLAGS) $< -o $@
+
+.PHONY: clean
+
+clean:
+	$(RM) -r *.o $(TARGET_EXEC)

chapters/stack/intro/drills/tasks/local-var/support/local-var.asm

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+%include "printf32.asm"
+
+%define ARRAY_1_LEN 5
+%define ARRAY_2_LEN 7
+%define ARRAY_OUTPUT_LEN 12
+
+section .data
+
+array_1 dd 27, 46, 55, 83, 84
+array_2 dd 1, 4, 21, 26, 59, 92, 105
+array_output times 12 dd 0
+
+
+section .text
+
+extern printf
+global main
+main:
+    mov eax, 0 ; counter used for array_1
+    mov ebx, 0 ; counter used for array_2
+    mov ecx, 0 ; counter used for the output array
+
+merge_arrays:
+    mov edx, [array_1 + 4 * eax]
+    cmp edx, [array_2 + 4 * ebx]
+    jg array_2_lower
+array_1_lower:
+    mov [array_output + 4 * ecx], edx
+    inc eax
+    inc ecx
+    jmp verify_array_end
+array_2_lower:
+    mov edx, [array_2 + 4 * ebx]
+    mov [array_output + 4 * ecx], edx
+    inc ecx
+    inc ebx
+
+verify_array_end:
+    cmp eax, ARRAY_1_LEN
+    jge copy_array_2
+    cmp ebx, ARRAY_2_LEN
+    jge copy_array_1
+    jmp merge_arrays
+
+copy_array_1:
+    mov edx, [array_1 + 4 * eax]
+    mov [array_output + 4 * ecx], edx
+    inc ecx
+    inc eax
+    cmp eax, ARRAY_1_LEN
+    jb copy_array_1
+    jmp print_array
+copy_array_2:
+    mov edx, [array_2 + 4 * ebx]
+    mov [array_output + 4 * ecx], edx
+    inc ecx
+    inc ebx
+    cmp ebx, ARRAY_2_LEN
+    jb copy_array_2
+
+print_array:
+    PRINTF32 `Array merged:\n\x0`
+    mov ecx, 0
+print:
+    mov eax, [array_output + 4 * ecx]
+    PRINTF32 `%d \x0`, eax
+    inc ecx
+    cmp ecx, ARRAY_OUTPUT_LEN
+    jb print
+
+    PRINTF32 `\n\x0`
+    xor eax, eax
+    ret