cleaned up comments

02/README.md

@@ -157,6 +157,9 @@ Numbers cannot appear at the end of a line (this made
 the compiler simpler to write), so I'm adding a `.` at the end of
 each one to avoid making that mistake.
 
+The code for `cmp rax, rbx` is now included in all conditional jump instructions
+(I kept forgetting to put `cm` before conditional jumps when writing this compiler).
+
 Anything after a command is treated as a comment;
 additionally `//` can be used for comments on their own lines.
 I decided to implement this as simply as possible:

02/in01

@@ -42,7 +42,7 @@ the segment we're loading in includes the ELF header at address 0x400000, so we
 ;im;01;00;00;00;00;00;00;00 write
 ;sy
 
--- read command (0x400174) --
+-- read a command (0x400174) --
 ;im;03;00;00;00;00;00;00;00 input file descriptor
 ;JA
 ;im;88;00;40;00;00;00;00;00 where to read to
@@ -184,7 +184,7 @@ okay we now have a digit in rbx
 ;AR
 ;<I;04
 ;+B
-;RA    store away in rbp
+;RA    store number away in rbp
 ;jm;38;ff;ff;ff  continue loop
 
 unused padding
@@ -316,7 +316,7 @@ convert bytes to an offset
 ;BA
 offset in rbx
 
-look in the label table
+read value from label table
 ;im;00;00;42;00;00;00;00;00
 ;+B
 ;BA
@@ -366,7 +366,7 @@ it's not a label or a number. let's look it up in the instruction table.
 ;im;d0;0a;40;00;00;00;00;00   start of instruction table
 ;+B
 ;BA
-;RA    store away address of command text in rbp
+;RA    store away pointer to command text in rbp
 ;zA;lb
 ;DA    number of bytes to write (used for syscall if command exists)
 ;BA
@@ -388,7 +388,7 @@ bad command!
 ;00;00;00;00;00;00;00;00;00;00;00;00;00;00;00;00
 
 this is a real command
-;BR   get address of command text back in rbx
+;BR   get pointer to command text back in rbx
 ;im;01;00;00;00;00;00;00;00 add 1 because we don't want to write the length 
 ;+B
 ;IA   address of data to write

03/in02

@@ -539,7 +539,7 @@ im
 ##43. ascii 'C'
 je
 :-<c  non-constant shift
-// write shl rax,
+// write shl rax, imm8 prefix
 im
 --<I
 IA
@@ -595,7 +595,7 @@ im
 ##43. ascii 'C'
 je
 :->c  non-constant shift
-// write shr rax,
+// write shr rax, imm8 prefix
 im
 -->I
 IA
@@ -651,7 +651,7 @@ im
 ##43. ascii 'C'
 je
 :-]c  non-constant shift
-// write sar rax,
+// write sar rax, imm8 prefix
 im
 --]I
 IA
@@ -803,7 +803,7 @@ im
 --r#
 cl
 DA
-// get index of first register
+// get index of second register
 im
 ##2.
 BA
@@ -884,7 +884,7 @@ im
 cl
 BA  put number in rbx
 im
---im  put immediate in rax
+--im  emit "mov rax, (immediate)"
 cl
 im
 --1A  transfer immediate to output
@@ -1000,7 +1000,7 @@ im
 cl    put rax in output
 jm
 :-rl
-// emit 'B = line[1]', i.e. deal with address of store instruction
+// set rbx to register referred to by line[1], i.e. deal with the address of a store instruction
 ::s@
 im
 ##1.
@@ -1173,7 +1173,7 @@ lb
 BA
 // note: for this we allow numerical operands, e.g. 'C+=d1'
 // we don't need this for ::B2 because it's only used for load instructions
-// (you don't normally need to dereference numerical literals)
+// (you don't normally need to dereference numbers)
 im
 ##41.  'A'
 je
@@ -1277,7 +1277,7 @@ BA
 zA
 jn     if on second pass,
 :-rl   ignore this (read next line)
-// first get current address
+// get current address
 im
 ##4. output fd
 JA
@@ -1303,7 +1303,7 @@ im
 --LI
 IA
 // copy from rsi to rdi until a newline is reached
-::lc  label copy
+::lc  label copy loop
 BI
 zA
 lb
@@ -1455,9 +1455,9 @@ im
 JA
 jm
 :-s= keep looping
-// emit "mov rax, immediate" -- with immediate in rbx
+// emit "mov rax, immediate" with immediate in rbx
 ::im
-// first, write prefix
+// first, emit the prefix
 im
 --IM
 IA
@@ -1574,7 +1574,8 @@ jm
 jm
 // conditional jump handling
 ::?j
-// note, we actually put the first operand in rbx and the second in rax. this is because A>0 is more familiar than 0<A
+// note, we actually put the first operand in rbx and the second in rax.
+// this is because A>0 is more familiar than 0<A
 im
 ##1. add 1 to line pointer to get pointer to 1st operand
 BA
@@ -2102,7 +2103,7 @@ BAs
 im
 ##41.
 je
-:-ca   call a
+:-ca   call A
 im
 ##5.  add 5 to line pointer to get pointer to label name
 BA
@@ -2889,7 +2890,7 @@ jm
 ~~
 ~~
 ~~
-::L$  end of current label list
+::L$  current end of label list
 --LB
 ::LB  labels
 ~~

04/in03

@@ -127,7 +127,7 @@ R=:line
 		!:read_line_loop_end
 :read_line_loop_end
 
-; remove whitespace (specifically, ' ' characters) at end of line
+; remove whitespace (specifically, space characters) at end of line
 I=R
 :remove_terminal_whitespace_loop
 	I-=d1

05/README.md

@@ -90,7 +90,9 @@ The C89 standard (in theory) defines which C programs are legal, and exactly wha
 A draft of it, which is about as good as the real thing, is [available here](http://port70.net/~nsz/c/c89/c89-draft.html).
 
 Since 1989, more features have been added to C, and so more C standards have been published.
-To keep things simple, our compiler only supports the features from C89 (with a few exceptions).
+To keep things simple, our compiler only supports the features from C89, except
+that declarations can appear after statements and `//` single-line comments are allowed
+(both of these were added in C99).
 
 
 ## compiler high-level details

README.md

@@ -149,6 +149,7 @@ ax  bx  cx  dx  sp  bp  si  di
 │ mov rbp, [rsp]       │ 48 8b 2c 24       │ load 8 bytes from rsp into rbp         │
 │ lea rax, [rbp+IMM32] │ 48 8d 85 IMM32    │ set rax to rbp+IMM32                   │
 │ lea rsp, [rbp+IMM32] │ 48 8d a5 IMM32    │ set rsp to rbp+IMM32                   │
+| int3                 | cc                | raise trap signal -useful for debugging|
 | movsq                | 48 a5             | copy 8 bytes from rsi to rdi           |
 | rep movsb            | f3 a4             | copy rcx bytes from rsi to rdi         |
 │ push rax             │ 50                │ push rax onto the stack                │
@@ -220,6 +221,7 @@ SYSCALLS
 Arguments are passed in
 	rdi, rsi, rdx, r10, r8, r9
 The return value is placed in rax.
+The values of rsp, rbp and rbx are preserved, but other registers might change.
 ```
 
 ## license