146 lines
3.9 KiB
Plaintext
146 lines
3.9 KiB
Plaintext
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include include/syscalls.i
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section .text,text
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; Frees the memory block pointed to by a0
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; free_w_size internal entry expecting size in d0
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; instead of 4 bytes before passed in address
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public free
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free:
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move.l -(a0), d0 ; Read the allocatuon size and get the true hole pointer
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free_w_size:
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move.l (free_list), a1 ; Get the head of the free list in a0
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cmpa.l #0, a1 ; Check if the free list is empty
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bne.b free_list_not_empty ; If not, find the right position and insert the hole
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move.l d0, (a0) ; Otherwise, set the free list to be the passed in hole and return
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move.l #0, ($4,a0)
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move.l a0, (free_list)
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rts
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free_list_not_empty:
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move.l a2, -(a7) ; Preserve a2 (callee saved)
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move.l #0, a1 ; a1 is the pointer to the previous hole in the list, starts out NULL
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move.l (free_list), a2 ; a2 is the pointer to the current hole in the list
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free_find_loop:
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cmpa.l #0, a2 ; If we have hit the end of the list, we have found the right position
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beq.b free_find_loop_done
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cmp.l a0, a2
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bgt.b free_find_loop_done
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move.l a2, a1 ; Go to the next item
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move.l ($4,a2), a2
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bra.b free_find_loop
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free_find_loop_done:
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; We have now found where to put the hole, that being between a1 (previous hole), and a2 (current hole)
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cmpa.l #0, a1 ; If there is no previous item, we cannot merge
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beq.b free_no_prev
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move.l (a1), d1 ; If size of prev hole + address of prev hole = address of hole to free, they are consecutive and can be merged
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add.l a1, d1
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cmp.l a0, d1
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bne.b free_no_prev_merge
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add.l d0, (a1) ; size of prev hole += size of hole to free
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move.l a1, a0 ; hole to free = prev hole
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move.l #0, a1 ; prev hole = NULL
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bra.b free_prev_merge_done
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free_no_prev_merge:
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move.l a2, ($4,a0) ; If we are not merging, hole to free next = current hole, prev hole next = hole to free
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move.l a0, ($4,a1)
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bra free_prev_merge_done
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free_no_prev:
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move.l (free_list), ($4,a0) ; If there is no previous hole, add it to the beginning of the free list
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move a0, (free_list)
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free_prev_merge_done:
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cmpa.l #0, a2 ; If there is no current hole, no merging must be done
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beq.b free_curr_merge_done
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move.l (a0), d1 ; If size of hole to free + address of hole to free = address of current hole, they are consecutive and can be merged
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add.l a0, d1
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cmp.l a2, d1
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bne.b free_curr_merge_done
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move.l ($4,a2), d1 ; hole to free next = current hole next
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move.l d1, ($4,a0)
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move.l (a0), d1 ; hole to free size += current hole size
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add.l (a2), d1
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move.l d1, (a0)
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free_curr_merge_done:
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move.l (a7)+, a2 ; Restore a2 (callee saved)
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rts
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; Allocates a memory block of size d0 and returns the address in a0
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public malloc
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malloc:
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; Return NULL if d0=0
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cmpi.l #0, d0
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bne .1
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move.l #0, a0
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rts
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.1:
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; d0=d0+4 rounded to next multiple of 4
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addi.l #4, d0
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move.l d0, d1
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andi.l #$2, d1
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beq.b .2
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move.l d0, d1
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andi.l #~$2, d1
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addi.l #8, d1
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move.l d1, d0
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.2:
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move.l (free_list), a0
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malloc_find_loop:
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cmpa.l #0, a0
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beq malloc_found_end
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move.l (a0), d1
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cmp.l d0, d1
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blt.b malloc_too_small
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beq.b malloc_block_exact_size
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sub.l d0, d1
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move.l d1, (a0)
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adda.l d1, a0
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move.l d0, (a0)+
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rts
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malloc_block_exact_size:
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adda.l #4, a0
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rts
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malloc_too_small:
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move.l ($8,a0), a0
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bra.b malloc_find_loop
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malloc_found_end:
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move.l d0, -(a7)
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move.l d0, d1
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andi.l #$fff, d1
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beq.b .1
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move.l d0, d1
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andi.l #~$fff, d1
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addi.l #$1000, d1
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move.l d1, d0
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.1:
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lsr.l #8, d0
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lsr.l #4, d0
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move.l d0, -(a7)
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jsr alloc_pages
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move.l (a7)+, d0
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lsl.l #8, d0
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lsl.l #4, d0
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move.l d0, d1
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move.l (a7)+, d0
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sub.l d0, d1
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move.l a0, a1
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adda.l d1, a1
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move.l d0, (a1)+
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move.l d1, d0
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move.l a1, -(a7)
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bsr.w free_w_size
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move.l (a7)+, a0
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rts
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; Allocate a block of memory d0 pages in length and returns the address in a0
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weak alloc_pages
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alloc_pages:
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move.l d2, -(a7)
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move.l #$2, d1
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jsr syscall_vmem_map_free
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alloc_pages_done:
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move.l (a7)+, d2
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rts
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section .bss,bss
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free_list:
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ds.b 4
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