@hackage risc3860.0.20210125

risc386 -- Restricted Instruction Set i386 simulator (C) 2013, Andreas Abel, Ludwig-Maximilians-University Munich

The main purpose of this simulator is to test i386 code generated by a compiler before register allocation. Therefore, it supports temporaries, an potentially infinite amount of extra registers t. (Of course, it can also be used to execute symbolic assembler after register allocation.)

The supported instruction set is very restricted but sufficient to write a compiler for MiniJava [Andrew Appel, Modern Compiler Implementation in Java].

I. System requirements:

You need a recent version of the Haskell Platform.

II. Installation:

1. Change to a temporary directory.

2. Unpack the tar ball

   tar xzf risc386-x.y.z.tar.gz

3. Change to the unpacked directory

   cd risc386-x.y.z

4. Install using Haskell's packet manager cabal

   cabal install

III. Running the simulator:

risc386 input-file.s

IV. Format of the input file:

The input file must be symbolic assembler in Intel format.

Here is a small example:

    .intel_syntax
    .global Lmain
    .type Lmain, @function

Lmain: #args enter 0, 0 L0: push 8 call L_halloc add %esp, 4 mov t1001, %eax push t1001 call LC$value add %esp, 4 mov t1002, %eax push t1002 call L_println_int add %esp, 4 L1: leave ret

    .global LC$value
    .type LC$value, @function

LC$value: #args LOC 0 enter 0, 0 L2: mov t1004, DWORD PTR [%ebp+8] mov DWORD PTR [t1004+4], 555 mov t1003, DWORD PTR [%ebp+8] mov %eax, DWORD PTR [t1003+4] L3: leave ret

Lexing rules: (If you want to be sure, read the .x file, the lexer specification.)

* White space is ignored (except as separator for alphanumeric tokens).

* Lines beginning with a dot '.' are skipped.
  These lines are pragmas for the symbolic assembler,
  which risc386 ignores.

* Lines beginning with a hash-symbol followed by a space '# '
  are comments, which are ignored as well.

* Lines beginning with a hash followed by a non-space character
  are risc386 pragmas and not ignored.

  Currently, risc386 only recognizes the pragma '#args'.

* Valid tokens are:

    #args LOC REG

    [ ] : , . + - *
    dword ptr                    DWORD PTR

    mov lea                      MOV LEA
    add sub imul                 ADD SUB IMUL
    idiv inc dec neg             IDIV INC DEC NEG
    shl shr sal sar              SHL SHR SAL SAR
    and or xor                   AND OR XOR
    not                          NOT
    cmp                          CMP
    je jne jl jle jge            JE JNE JL JLE JGE
    jmp call ret                 JMP CALL RET
    push pop enter leave         PUSH POP ENTER LEAVE
    nop                          NOP

    eax ebx ecx edx esi edi ebp esp
    %eax %ebx %ecx %edx %esi %edi %ebp %esp

    <number>    (given by reg.ex [0-9]+)
    t<number>   (denoting a temporary register)

    <ident>     (given by reg.ex. [a-zA-Z][a-zA-Z0-9_'$]*)

  Identifiers are used for labels.

Parsing rules: (If you want to know all of them, read the .y file)

1. The input file must be a sequence of procedures.

   There must be one procedure whose name ends in 'main'.
   This one is taken as the entry point.

2. Each procedure starts with a label and ends with a return
   instruction. Optionally, it can be preceded by a declaration
   of its arguments

              #args REG %eax, LOC 0, LOC 4
     Lmyproc:
              ...
              RET

   Lmyproc expects its first argument in register %eax,
   its second at [%esp+0] and its third at [%esp+4].
   The stack addresses are to be taken *before* the CALL
   is executed (which will put the return address on the stack
   and shift the relative location of the arguments by +4).

3. The body of each procedure is a list of i386 assembler
   instructions in Intel syntax.  The supported instructions
   are listed above.

   Each instruction my be preceded by a label.

   Conditional and unconditional jumps are only allowed to
   a label, and only to one defined in the same procedure.
   Cross-procedure jumps or jumps to a calculated address
   are not supported.

   CALLs are only defined to a procedure label.
   risc386 assumes the cdecl calling convention.

4. Restrictions for individual instructions:

   RET    does accept arguments
   ENTER  is only supported in the form ENTER <number>, 0

Runtime:

risc386 knows a number of predefined procedures.  They expect
their arguments on the stack (cdecl calling convention) and
return the result in %eax.

L_halloc
  1 Argument: number of bytes to allocate on the heap
  Result    : pointer to first allocated byte.

L_println_int
  1 Argument: signed 32bit integer value to print
  Result    : nothing

L_print_char
  1 Argument: unicode char (32bit) to print
  Result    : nothing

L_raise
  1 Argument: error code
  Result    : nothing, does not return, stops execution

Execution specialties:

risc386 supports 4 different types, all of size 32 bits:

  1. Signed integers.

  2. Heap addresses.

     Heap addresses consist of a base address which was obtained
     by L_halloc plus an offset.  The offset must be a multiple of 4.

  3. Stack addresses.

     %esp and %ebp may only be loaded with stack addresses.

  4. Return addresses.

     Get pushed onto the stack by a CALL.

     RET checks that a return address lies on top of the stack
     before returning.  The content of the return address is
     ignored, RET jumps back to the procedure where the matching
     CALL was issued.

CMP is the only command that sets flags.

CALL saves all temporary registers, RET restores them.