TJ version

Author: davidad

concurrency.asm

@@ -3,7 +3,7 @@
   ; Initialize constants.
   mov r12, 65537                 ; Exponent to modular-exponentiate with
   mov rbx, 235                   ; Modulus to modular-exponentiate with
-  mov r15, NPROCS                ; Number of processes to fork.
+  mov r15, NPROCS                ; Number of worker processes to fork.
   mov r14, (SIZE+1)*8            ; Size of shared memory; reserving first
                                  ; 64 bits for bookkeeping
 
@@ -13,50 +13,47 @@
 
 open_file:
   ; We have a file specified on the command line, so open() it.
-  mov rax, SYSCALL_OPEN
-  mov rdi, [rsp+2*8]
-  mov rsi, O_RDWR|O_CREAT        ; read/write mode; create if necessary
-  mov rdx, 0o660                 ; `chmod`-mode of file to create (octal)
-  syscall
+  mov rax, SYSCALL_OPEN          ; set up open()
+  mov rdi, [rsp+2*8]               ; filename from command line
+  mov rsi, O_RDWR|O_CREAT          ; read/write mode; create if necessary
+  mov rdx, 660o                    ; `chmod`-mode of file to create (octal)
+  syscall                        ; do open() system call
   mov r13, rax                   ; preserve file descriptor in r13
-  mov rax, SYSCALL_PWRITE        ; adjust file size by writing to "end"
-  mov rdi, r13
-  mov rsi, null_byte             ; write a null byte
-  mov rdx, 1                     ; just one byte
-  mov r10, r14                   ; at offset of our desired file size
-  dec r10                        ; minus one
-  syscall
+  mov rax, SYSCALL_FTRUNCATE     ; set up ftruncate() to adjust file size
+  mov rdi, r13                     ; file descriptor
+  mov rsi, r14                     ; desired file size
+  syscall                        ; do ftruncate() system call
   mov r8,  r13
   mov r10, MAP_SHARED
   jmp mmap
 
+  ; Ask the kernel for a shared memory mapping.
 map_anon:
-  mov r10, MAP_SHARED|MAP_ANON   ; MAP_ANON means not backed by a file
-  mov r8,  -1                    ; thus our file descriptor is -1
+  mov r10, MAP_SHARED|MAP_ANON     ; MAP_ANON means not backed by a file
+  mov r8,  -1                      ; thus our file descriptor is -1
 mmap:
-  mov r9,   0                    ; ...and there's no file offset in either case.
-  ; Ask the kernel for a shared memory mapping.
-  mov eax, SYSCALL_MMAP
-  mov rdx, PROT_READ|PROT_WRITE  ; We'd like a read/write mapping
-  mov rdi,  0                    ; at no pre-specified memory location.
-  mov rsi, r14                   ; Length of the mapping in bytes.
-  syscall                        ; Do system call.
+  mov r9,   0                      ; and there's no file offset in either case.
+  mov rax, SYSCALL_MMAP          ; set up mmap()
+  mov rdx, PROT_READ|PROT_WRITE    ; We'd like a read/write mapping
+  mov rdi,  0                      ; at no pre-specified memory location.
+  mov rsi, r14                     ; Length of the mapping in bytes.
+  syscall                        ; do mmap() system call.
   test rax, rax                  ; Return value will be in rax.
   js error                       ; If it's negative, that's trouble.
   mov rbp, rax                   ; Otherwise, we have our memory region [rbp].
 
-  lock add [rbp], r15            ; Initialize the first machine word to NPROCS.
+  lock add [rbp], r15            ; Add NPROCS to the file's first machine word.
                                  ; We'll use it to track the # of still-running
-                                 ; processes.
+                                 ; worker processes.
 
   ; Next, fork NPROCS processes.
 fork:
   mov eax, SYSCALL_FORK
   syscall
-%ifidn __OUTPUT_FORMAT__,elf64
+%ifidn __OUTPUT_FORMAT__,elf64     ; (This means we're running on Linux)
   test rax, rax                  ; We're a child iff return value of fork()==0.
   jz child
-%elifidn __OUTPUT_FORMAT__,macho64
+%elifidn __OUTPUT_FORMAT__,macho64 ; (This means we're running on OSX)
   test rdx, rdx                  ; Apple...you're not supposed to touch rdx here
   jnz child                      ; Apple, what
 %endif
@@ -66,7 +63,7 @@ fork:
 parent:
   pause
   cmp qword [rbp], 0
-  jnz parent                     ; Wait for [rbp] to be zero
+  jnz parent                     ; Wait for [rbp], the worker count, to be zero
 %ifndef NOPRINT
   mov rbx, rbp
   add rbx, r14                   ; rbx marks the end of the [rbp] region
@@ -84,7 +81,7 @@ print_loop:
   jne print_loop
 %endif
 
-success:
+exit_success:
   mov eax, SYSCALL_EXIT          ; Normal exit
   mov edi, 0
   syscall
@@ -102,17 +99,17 @@ find_work:                       ; and try to find a piece of work to claim
   jz found_work                  ; If successful, zero flag is set
 .moveon:
   add rdi, 8                     ; Otherwise, try a different piece.
-.next:
+find_work.next:
   cmp rdi, rsi                   ; Make sure we haven't hit the end.
   jne find_work
 
 child_exit:                      ; If we have hit the end, we're done.
   lock dec qword [rbp]           ; Atomic-decrement the # of active processes.
-  jmp success
+  jmp exit_success
 
 found_work:
-  mov r8, 8                      ; There are 8 tasks per piece.
-do_task:                       ; This part does the actual work of mod-exp.
+  mov r8, 8                      ; There are 8 pieces per task.
+do_piece:                       ; This part does the actual work of mod-exp.
   mov r13, r12                   ; Copy exponent to r13.
   mov rax, rdi                   ; The actual value to mod-exp should start
   sub eax, 0x7                   ; at 1 for the first byte after the bookkeeping
@@ -137,9 +134,9 @@ do_task:                       ; This part does the actual work of mod-exp.
   jnz .modexploop                ; If the exponent isn't zero, keep working
   mov byte [rbp+rdi], al         ; Else, store result byte.
   inc rdi                        ; Move forward
-  dec r8                         ; Decrement task counter
-  jnz do_task                    ; Do the next task if there is one.
-  jmp find_work.next             ; Else, find the next piece of work.
+  dec r8                         ; Decrement piece counter
+  jnz do_piece                   ; Do the next piece if there is one.
+  jmp find_work.next             ; Else, find the next task.
 
 error:
   mov rdi, rax                   ; In case of error, return code is -errno...
@@ -152,10 +149,4 @@ error:
   section .data
   unsigned_int:
     db `%u\n`
-  null_byte:
-    db 0
-%else
-  section .data
-  null_byte:
-    db 0
 %endif

os_dependent_stuff.asm

@@ -1,22 +1,24 @@
 ; syscalls
 %ifidn __OUTPUT_FORMAT__,elf64
 ; http://lxr.linux.no/linux+v3.13.5/arch/x86/syscalls/syscall_64.tbl
-  %define SYSCALL_OPEN    2
-  %define SYSCALL_WRITE   1
-  %define SYSCALL_MMAP    9
-  %define SYSCALL_PWRITE  18
-  %define SYSCALL_FORK    57
-  %define SYSCALL_WAITID  247
-  %define SYSCALL_EXIT    60
+  %define SYSCALL_OPEN      2
+  %define SYSCALL_WRITE     1
+  %define SYSCALL_MMAP      9
+  %define SYSCALL_FTRUNCATE 77
+  %define SYSCALL_PWRITE    18
+  %define SYSCALL_FORK      57
+  %define SYSCALL_WAITID    247
+  %define SYSCALL_EXIT      60
 %elifidn __OUTPUT_FORMAT__,macho64
 ; http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/bsd/kern/syscalls.master
-  %define SYSCALL_OPEN    0x2000005
-  %define SYSCALL_WRITE   0x2000004
-  %define SYSCALL_MMAP    0x20000C5
-  %define SYSCALL_PWRITE  0x200009A
-  %define SYSCALL_FORK    0x2000002
-  %define SYSCALL_WAITID  0x20000AD
-  %define SYSCALL_EXIT    0x2000001
+  %define SYSCALL_OPEN      0x2000005
+  %define SYSCALL_WRITE     0x2000004
+  %define SYSCALL_MMAP      0x20000C5
+  %define SYSCALL_FTRUNCATE 0x20000C9
+  %define SYSCALL_PWRITE    0x200009A
+  %define SYSCALL_FORK      0x2000002
+  %define SYSCALL_WAITID    0x20000AD
+  %define SYSCALL_EXIT      0x2000001
 %endif
 
 ; fcntls