about summary refs log blame commit diff stats
path: root/053new-segment.subx
blob: 51f321fdadc909ca630d47928d7f02f4e5830932 (plain) (tree)
1
2
3
4
5
6
7
8
9
10
11
12











                                                                               

       


                                                                                                                                                 
 
                      
                                                           

                          
                                                                                                                                                                       
                             
                   
               
                         
              
                               
                      







                                                                                                                                                                        
                         
 
                                                               
                

                                                                                                                                                                       
                      

               
                                        

                                                                                                                                                                                          
                             

                                           
                         







                                                                                                                                                                             
                 
                         

                 
                

                                                                                                                                                                       
             

       
 
                                                                                             
                                          
          
           
                      
         
           
                      
                                     
                   
                                             
        
                                                
            
                                               
 
                            
# Create a new segment (pool of memory for allocating chunks from) in the form
# of an *allocation descriptor* that can be passed to the memory allocator
# (defined in a later layer).
#
# Currently an allocation descriptor consists of just the bounds of the pool of
# available memory:
#
#   curr : address
#   end : address
#
# This isn't enough information to reclaim individual allocations. We can't
# support arbitrary reclamation yet.

== code
#   instruction                     effective address                                                   register    displacement    immediate
# . op          subop               mod             rm32          base        index         scale       r32
# . 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes

Entry:   # manual test
    # var ad/ecx : (address allocation-descriptor) = {0, 0}
    68/push  0/imm32/limit
    68/push  0/imm32/curr
    89/copy                         3/mod/direct    1/rm32/ecx    .           .             .           4/r32/esp   .               .                 # copy esp to ecx
    # new-segment(0x1000, ad)
    # . . push args
    51/push-ecx
    68/push  0x1000/imm32
    # . . call
    e8/call  new-segment/disp32
    # . . discard args
    81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
    # eax = ad->curr
    8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/eax   .               .                 # copy *ecx to eax
    # write to *eax to check that we have access to the newly-allocated segment
    c7          0/subop/copy        0/mod/direct    0/rm32/eax    .           .             .           .           .               0x34/imm32        # copy to *eax
    # syscall(exit, eax)
    89/copy                         3/mod/direct    3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to ebx
    b8/copy-to-eax  1/imm32/exit
    cd/syscall  0x80/imm8

new-segment:  # len : int, ad : (address allocation-descriptor)
    # . prologue
    55/push-ebp
    89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
    # . save registers
    50/push-eax
    53/push-ebx
    # copy len to _mmap-new-segment->len
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # copy *(ebp+8) to eax
    89/copy                         0/mod/indirect  5/rm32/.disp32            .             .           0/r32/eax   _mmap-new-segment:len/disp32      # copy eax to *_mmap-new-segment:len
    # mmap(_mmap-new-segment)
    bb/copy-to-ebx  _mmap-new-segment/imm32
    b8/copy-to-eax  0x5a/imm32/mmap
    cd/syscall  0x80/imm8
    # copy {eax, eax+len} to *ad
    # . ebx = ad
    8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .             .           3/r32/ebx   0xc/disp8       .                 # copy *(ebp+12) to ebx
    # . *ebx = eax
    89/copy                         0/mod/indirect  3/rm32/ebx    .           .             .           0/r32/eax   .               .                 # copy eax to *ebx
    # . *(ebx+4) = eax+len
    03/add                          1/mod/*+disp8   5/rm32/ebp    .           .             .           0/r32/eax   8/disp8         .                 # add *(ebp+8) to eax
    89/copy                         1/mod/*+disp8   3/rm32/ebx    .           .             .           0/r32/eax   4/disp8         .                 # copy eax to *(ebx+4)
$new-segment:end:
    # . restore registers
    5b/pop-to-ebx
    58/pop-to-eax
    # . epilogue
    89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
    5d/pop-to-ebp
    c3/return

== data

# various constants used here were found in the Linux sources (search for file mman-common.h)
_mmap-new-segment:  # type mmap_arg_struct
    # addr
    0/imm32
_mmap-new-segment:len:
    # len
    0/imm32
    # protection flags
    3/imm32  # PROT_READ | PROT_WRITE
    # sharing flags
    0x22/imm32  # MAP_PRIVATE | MAP_ANONYMOUS
    # fd
    -1/imm32  # since MAP_ANONYMOUS is specified
    # offset
    0/imm32  # since MAP_ANONYMOUS is specified

# . . vim:nowrap:textwidth=0