more work

.gitignore

@@ -2,3 +2,4 @@
 *.pdb
 *.obj
 *sublime-workspace
+*.exe

README.md

@@ -0,0 +1,8 @@
+This repo is me working through the book The Art of 64 Bit Assembly. 
+To build listings in the `src/` folder simply call the `build.bat`
+script with the listing number:
+
+```batch
+build 1_8 //  don't add .asm extension
+
+```

src/1_3.asm

@@ -0,0 +1,13 @@
+    .CODE
+
+    option casemap:none     ; make all symbols case sensitive (like C)
+
+    public asm_func         ; make this visible outside of this source
+
+asm_func PROC ; start procedure
+    
+    ret
+
+asm_func ENDP ; end procedure
+        
+    END

src/1_4.asm

@@ -0,0 +1,15 @@
+; a user defined proc
+
+    .code 
+
+asm_proc proc
+    ret             ; return from the procedure
+asm_proc endp
+
+main proc           ; the main procedure
+    call asm_proc   ; call our proc
+    ret
+main endp
+    end
+
+

src/1_5.asm

@@ -0,0 +1,21 @@
+    option casemap:none
+
+    .data
+
+fmt_str byte 'Hello World!', 10, 0 ; here 10 is the newline feed
+
+    .code
+
+    externdef printf:proc
+
+    public asm_func
+
+asm_func proc
+    sub rsp, 56
+    lea rcx, fmt_str ; load the format string into the RCX register to be used by the printf
+    call printf
+    add rsp, 56
+    ret
+asm_func endp
+    
+    end

src/1_8.asm

@@ -1,61 +1,61 @@
-; assembly that shows how to return values to a
-; a C function
-
     option casemap:none
 
 ; constants
-nl      =       10
-maxlen  =       256
+nl      =   10  ; newline
+maxlen  =   256 ; max len of the string
 
     .data
 
-title_str   byte        "Listing 1-8", 0
-prompt      byte        "Enter a string: ", 0
-fmt_string  byte        "User entered: '%s'", nl, 0
-
-; make `maxlen` copies/duplicates of size byte, each uinitialized
-input       byte maxlen dup (?)
+title_string    byte    'Listing 1_8', 0
+prompt_string   byte    'Enter a string: ', 0
+format_string   byte    'User entered: "%s" ', nl, 0
 
+input   byte    maxlen dup (?) ; make maxlen copies of byte, each uninitialized
 
     .code
 
     externdef printf:proc
     externdef readline:proc
 
-    public get_title
 
-; procedure loads the address of the title_str into the RAX
-; register, this is the register where C expects to find 
-; the return of this proc. (WINDOWS ABI)
+;; get_title procedure -------------------------
+;; get_title moves the address of the byte containing the string "Listing 1_8", 0
+;; into the RAX register, it does this usig the LEA instruction
+    public get_title
 get_title proc
     
-    lea rax, title_str  ; load address of title string in RAX register
-    ret
+    lea rax, title_string   ; load address of title_string into rax
+    ret 
 
 get_title endp
 
-; ASM Main function
     public asm_main
-asm_main proc 
+asm_main proc
 
-    sub     rsp, 56
-    
-    lea     rcx, prompt     ; load prompt string address into RCX register
-    call    printf          ; this is the reigster where ABI tells us to place arguments
+    sub rsp, 56
 
-    mov     input, 0        ; ensure the input string is terminated with 0
+    ;; first we want to print a prompt, to do this we use the stdio function printf, 
+    ;; we need to make the arguments for printf avaialble by loading the address of the
+    ;; byte prompt_string into RCX
+    lea rcx, prompt_string
+    call printf
 
-    lea     rcx, input      ; load input address to rcx register
-    mov     rdx, maxlen     ; move maxlen into rdx register
-    call    readline        ; use rcx and rdx as arguments to call readline
+    mov input, 0 ;; clear the input
 
-    lea     rcx, fmt_string
-    lea     rdx, input
-    call    printf
+    ; read user input by calling readline from out cpp program. We load the required 
+    ; arguments into the registers RCX, and RDX and then call readline
+    lea rcx, input
+    mov rdx, maxlen
+    call readline
 
-    add     rsp, 56
+    ; load RCX and RDX with arugments to printf, to print back to the user
+    lea rcx, format_string
+    lea rdx, input
+    call printf
+
+    add rsp, 56
     ret
 
 asm_main endp
 
-    end
+    end

src/build.bat

@@ -1,4 +1,9 @@
 @echo off
 echo ~~~~ starting build ~~~~
+
+REM /nolog is dont show MS info at run
+REM /c is compile dont link
+REM /Zi is debug info
+REM /Cp is preserve cases
 ml64 /nologo /c /Zi /Cp %1.asm
 cl /nologo /O2 /Zi /utf-8 /EHa /Fe%1.exe c.cpp %1.obj

src/c.cpp

@@ -8,7 +8,7 @@ extern "C"
 {
     void asm_main(void);
 
-
+    // function is defined in the asm file
     char *get_title(void);
 
     int readline(char* dest, int maxlen);

src/listing_1_9.cpp

@@ -0,0 +1 @@
+listing_1_9.cpp

src/main.cpp

@@ -2,12 +2,15 @@
 
 extern "C" 
 {
-    void asm_func(void);
-};
+    // Function written in ASM
+    void asm_func(void);    
+}
 
-int main(void) 
+int main() 
 {
-    printf("calling asm main\n");
+    printf("calling asm function\n");
     asm_func();
-    printf("return from asm main\n");
+    printf("returned from asm function\n");
+
+    return(0);
 }