misc: less useless comments; document utility functions; follow the AAPCS calling convention

.asm-lsp.toml

@@ -0,0 +1,7 @@
+[default_config]
+version = "0.10.0"
+instruction_set = "arm"
+assembler = "gas"
+
+[default_config.opts]
+compiler = "arm-linux-gnueabihf-gcc"

.gitignore

@@ -0,0 +1,2 @@
+*.out
+out

constants.S

@@ -0,0 +1,9 @@
+
+/* Linux standard file descriptors  */
+.equ STDIN,  0x0
+.equ STDOUT, 0x1
+.equ STDERR, 0x2
+
+.equ ENOENT,       0xFFFFFFFE
+.equ ENOTDIR,      0xFFFFFFEC
+

errors.S

@@ -1,4 +0,0 @@
-
-.equ ENOENT,       0xFFFFFFFE
-.equ ENOTDIR,      0xFFFFFFEC
-

main.S

@@ -1,18 +1,33 @@
 .include "syscalls.S"
-.include "errors.S"
+.include "constants.S"
+.include "string.S"
 
 .global _start
 
-exit: @ r0 should have the status code to exit with
+/*
-    mov r7, #SYS_EXIT @ Move the exit syscall number to r7 (which is the register svc reads to know which syscall to execute)
+    Exits the program with the provided exit code
-    svc 0 @ execute the syscall
 
-print: @ r1 => buffer to print. r2 => how many bytes to print. clobbers r0
+    @args:
-    @ print to stdout
+        r0 => exit code
-    mov r0, #1 @ Use STDOUT fd as the write fd
+*/
-    mov r7, #SYS_WRITE @ call write(2)
+exit:
+    mov r7, #SYS_EXIT
     svc 0
-    bx lr @ return to caller
+
+/*
+    print to stdout
+
+    @args:
+        r1 => pointer to buffer to print
+        r2 => how many bytes to print
+    @clobbers:
+        r0
+*/
+print:
+    mov r0, #STDOUT
+    mov r7, #SYS_WRITE
+    svc 0
+    bx lr
 
 open_fail:
     push {r0}
@@ -48,81 +63,12 @@ fd_not_found:
     mov r0, #1
     bl exit
 
-open_and_read_file:
-    @ open file
-    ldr r0, =FILE @ filepath
-    mov r1, #0 @ flags
-    mov r2, #0 @ mode_t
-    mov r7, #SYS_OPEN
-    svc 0
-
-    cmp r0, #0
-    blt open_fail
-
-    @ read the file contents
-    @ r0 needs the fd, which it should already be since the call to open() set r0 to the fd.
-    ldr r1, =buffer @ pointer to buffer to read into
-    mov r2, #50 @ how many bytes to read
-    mov r7, #SYS_READ
-    svc 0
-
-    @ print the contents of the buffer
-    ldr r1, =buffer
-    mov r2, #50 @ FIXME: hardcoded badness
-    bl print
-
-    ldr r1, =NEWLINE
-    mov r2, #1
-    bl print
-
-    mov r0, #0
-    bl exit
-
-strlen: @ r0 holds the string length. r1 should be a pointer to the start of the string.
-    mov r0, #0
-strlen_loop:
-    ldrb r2, [r1, r0]
-    cmp r2, #0
-    bxle lr
-
-    add r0, r0, #1
-    b strlen_loop
-
-direntry_loop:
-    cmp r4, r8
-    bxge lr
-
-    push {lr}
-
-    add r1, r5, #10 @ offset 10 bytes into the dirent struct to reach d_name.
-    bl strlen
-    mov r2, r0
-    bl print
-
-    ldr r1, =NEWLINE
-    mov r2, #1
-    bl print
-
-    pop {lr}
-
-    @ load the value (as 16-bits zero-extended as opposed to loading 32-bits and then extending that ourselves with UXTH)
-    @ in the memory address of r5 offset by 8 bytes to get us the d_reclen
-    ldrh r6, [r5, #8] 
-    add r5, r5, r6 @ skip to the next dirent
-
-    add r4, r4, r6 @ accumulate how many bytes we read
-
-    b direntry_loop
-
-@ TODO: alphabetically sort the directory entries before printing them.
 _start:
     ldr r0, [sp]
     cmp r0, #1
     ldrgt r0, [sp, #8]
     ldrle r0, =FALLBACK_DIR
 
-    @ open file
-    @ldr r0, =FALLBACK_DIR @ filepath
     mov r1, #0 @ flags
     mov r2, #0 @ mode_t
     mov r7, #SYS_OPEN
@@ -133,7 +79,6 @@ _start:
     cmp r0, #0
     blt open_fail
 
-    @ read the directory contents
     @ r0 needs the fd, which it should already be since the call to open() set r0 to the fd.
     ldr r1, =buffer @ pointer to linux_dirent structure
     @ TODO: we can allocate the required memory on the stack instead of in the bss section I think.
@@ -146,16 +91,36 @@ _start:
     cmp r0, #0
     blt dir_read_fail
 
-    mov r8, r0 @ store how many bytes the getdents syscall read, so we can use that to exit the direntry loop
     mov r4, #0 @ initialize r4 to 0
     ldr r5, =buffer
-    bl direntry_loop
+1:
+    push {r0}
+
+    add r1, r5, #10 @ offset 10 bytes into the dirent struct to reach d_name.
+    bl strlen
+    mov r2, r0
+    bl print
+
+    ldr r1, =NEWLINE
+    mov r2, #1
+    bl print
+
+    pop {r0}
+
+    @ load the value (as 16-bits zero-extended as opposed to loading 32-bits and then extending that ourselves with UXTH)
+    @ in the memory address of r5 offset by 8 bytes to get us the d_reclen
+    ldrh r6, [r5, #8] 
+    add r5, r5, r6 @ skip to the next dirent
+
+    add r4, r4, r6 @ accumulate how many bytes we read
+
+    cmp r4, r0
+    blt 1b
 
     mov r0, #0
     bl exit
 
 .data
-    FILE:           .asciz "/home/illusion/asm.txt"
     FALLBACK_DIR:   .asciz "."
     OPEN_FAIL:      .ascii "Failed to open file descriptor"
     DIR_READ_FAIL:  .ascii "Failed to read the directory\n"

string.S

@@ -0,0 +1,25 @@
+/*
+    Current implementation only counts the bytes instead of characters.
+
+    @args:
+        r1 => pointer to the string
+    @returns:
+        r0 => string length
+    @clobbers:
+        r2
+*/
+strlen:
+    mov r0, #0
+1:
+    ldrb r2, [r1, r0]
+    cmp r2, #0
+    bxle lr
+
+    add r0, r0, #1
+    b 1b
+
+/*
+    @input r1, r2 - pointers to the strings to compare
+    @return r0 - 0 if equal, -1 if a < b, 1 if a > b
+*/
+strcmp: @ TODO: implement