Soul of a tiny new machine. More thorough tests → More comprehensible and rewrite-friendly software → More resilient society.
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# A function which pushes n zeros on the stack.
# Really only intended to be called from code generated by mu.subx (for array
# vars on the stack).
== code
#? Entry:
#? # . prologue
#? 89/<- %ebp 4/r32/esp
#? #
#? 68/push 0xfcfdfeff/imm32
#? b8/copy-to-eax 0x34353637/imm32
#? $dump-stack0:
#? (push-n-zero-bytes 4)
#? 68/push 0x20/imm32
#? $dump-stack9:
#? b8/copy-to-eax 1/imm32/exit
#? cd/syscall 0x80/imm8
# This is not a regular function, so it won't be idiomatic.
# Registers must be properly restored.
# Registers can be spilled, but that modifies the stack and needs to be
# cleaned up.
# Overhead:
# 62 + n*6 instructions to push n bytes.
# If we just emitted code to push n zeroes, it would be:
# 5 bytes for 4 zero bytes, so 1.25 bytes per zero. And that's not even
# instructions.
# But on the other hand it would destroy the instruction cache, where this
# approach requires 15 instructions, fixed.
# n must be positive
push-n-zero-bytes: # n: int
$push-n-zero-bytes:prologue:
89/<- *Push-n-zero-bytes-ebp 5/r32/ebp # spill ebp without affecting stack
89/<- %ebp 4/r32/esp
$push-n-zero-bytes:copy-ra:
# -- esp = ebp
89/<- *Push-n-zero-bytes-eax 0/r32/eax
8b/-> *esp 0/r32/eax
2b/subtract *(ebp+4) 4/r32/esp
# -- esp+n = ebp
89/<- *esp 0/r32/eax
8b/-> *Push-n-zero-bytes-eax 0/r32/eax
$push-n-zero-bytes:bulk-cleaning:
89/<- *Push-n-zero-bytes-esp 4/r32/esp
81 0/subop/add *Push-n-zero-bytes-esp 4/imm32
81 0/subop/add *(ebp+4) 4/imm32
(zero-out *Push-n-zero-bytes-esp *(ebp+4)) # n+4
$push-n-zero-bytes:epilogue:
8b/-> *Push-n-zero-bytes-ebp 5/r32/ebp # restore spill
c3/return
== data
Push-n-zero-bytes-ebp: # (addr int)
0/imm32
Push-n-zero-bytes-esp: # (addr int)
0/imm32
Push-n-zero-bytes-eax:
0/imm32