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Unaligned R/W

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This commit is contained in:
Firebolt 2021-10-20 19:19:09 -04:00
parent 07489fe8cf
commit 5ebc409cc7
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GPG Key ID: 4219518A61A50458
1 changed files with 38 additions and 20 deletions
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54
runtime/luau.lua
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@ -38,6 +38,17 @@ local function rip_u64(x) return math.floor(x / 0x100000000), x % 0x100000000 en
local function merge_u64(hi, lo) return hi * 0x100000000 + lo end local function merge_u64(hi, lo) return hi * 0x100000000 + lo end
local function load_byte(memory, addr)
local offset = addr % 4
return bit32.rshift(memory.data[(addr - offset) / 4] or 0, 8 * offset)
end
local function store_byte(memory, addr, value)
local offset = addr % 4;
local base = (addr - offset) / 4;
memory.data[base] = bit32.bor(memory.data[base] or 0, bit32.lshift(value, 8 * offset));
end
-- Runtime functions -- Runtime functions
local function grow_page_num(memory, num) local function grow_page_num(memory, num)
local old = memory.min local old = memory.min
@ -97,9 +108,18 @@ extend.i32_u64 = no_op
function wrap.i64_i32(i) return i % 2 ^ 32 end function wrap.i64_i32(i) return i % 2 ^ 32 end
function load.i32(memory, addr) function load.i32(memory, addr)
if addr % 4 ~= 0 then error('unaligned read') end if addr % 4 == 0 then
-- aligned read
return memory.data[addr / 4] or 0 return memory.data[addr / 4] or 0
else
-- unaligned read
return bit32.bor(
load_byte(memory, addr),
bit32.lshift(load_byte(memory, addr + 1), 8),
bit32.lshift(load_byte(memory, addr + 2), 16),
bit32.lshift(load_byte(memory, addr + 3), 24)
)
end
end end
function load.i32_u8(memory, addr) function load.i32_u8(memory, addr)
@ -109,36 +129,34 @@ function load.i32_u8(memory, addr)
end end
function load.i64(memory, addr) function load.i64(memory, addr)
if addr % 4 ~= 0 then error('unaligned read') end local hi = load.i32(memory, addr)
local lo = load.i32(memory, addr + 4)
local hi = memory.data[addr / 4 + 1] or 0
local lo = memory.data[addr / 4] or 0
return merge_u64(hi, lo) return merge_u64(hi, lo)
end end
function store.i32(memory, addr, value) function store.i32(memory, addr, value)
if addr % 4 ~= 0 then error('unaligned write') end if addr % 4 == 0 then
-- aligned write
memory.data[addr / 4] = value memory.data[addr / 4] = value
else
-- unaligned write
store_byte(memory, addr, value)
store_byte(memory, addr + 1, bit32.rshift(value, 8))
store_byte(memory, addr + 2, bit32.rshift(value, 16))
store_byte(memory, addr + 3, bit32.rshift(value, 24))
end
end end
function store.i32_n8(memory, addr, value) function store.i32_n8(memory, addr, value)
if addr % 4 ~= 0 then error('unaligned write') end store.i32(memory, addr, bit32.band(value, 0xFF))
local old = bit32.band(memory.data[addr / 4] or 0, 0xFFFFFF00)
local new = bit32.band(value, 0xFF)
memory.data[addr / 4] = bit32.bor(old, new)
end end
function store.i64(memory, addr, value) function store.i64(memory, addr, value)
if addr % 4 ~= 0 then error('unaligned write') end
local hi, lo = rip_u64(value) local hi, lo = rip_u64(value)
memory.data[addr / 4] = lo store.i32(memory, addr, lo)
memory.data[addr / 4 + 1] = hi store.i32(memory, addr + 4, hi)
end end
return { return {