Strange LuaJIT segfault
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- Subject: Strange LuaJIT segfault
- From: Pierre Chapuis <catwell@...>
- Date: 2011年8月11日 19:49:52 +0200
Hello,
I have code that uses the FFI that segfaults when I run it in
LuaJIT-2.0.0-beta8 with hotfix #1 on Mac OS X. It is part of the code
that implements a bitset.
Here is a simplified version:
#!/usr/bin/env luajit -lluarocks.loader
local ffi = require "ffi"
local bmask_1,bmask_0 = ffi.new("uint8_t[8]"),ffi.new("uint8_t[8]")
local allones = bit.tobit(0xff)
for i=0,7 do
bmask_1[i] = bit.lshift(1,7-i)
bmask_0[i] = bit.bxor(allones,bmask_1[i])
end
local bit_set_0 = function(_bset,_byte,_bit)
io.stderr:write("A\n")
-- if _bit == 0 then end
local y = bmask_0[_bit]
io.stderr:write("B\n")
_bset[_byte] = bit.band(_bset[_byte],bmask_0[_bit])
end
local NBYTES = 30
local _bset = ffi.new("uint8_t[?]",NBYTES)
for i=1,2 do
local _byte,_bit = 0,-1
for j=1,NBYTES*8 do
_bit = _bit + 1
if _bit == 8 then _byte,_bit = _byte+1,0 end
io.stderr:write(_byte," ",_bit,"\n")
bit_set_0(_bset,_byte,_bit)
end
end
If I run this script, it segfaults at the beginning second iteration of
the loop (for i=1,2 do). The output is:
[...]
A
B
29 6
A
B
29 7
A
B
0 0
A
Segmentation fault
If I run it in GDB I get:
[...]
A
B
29 6
A
B
29 7
A
B
0 0
A
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000100085240
0x00000001390bfdea in ?? ()
It does NOT segfault for NBYTES < 22. It does NOT segfault if I
uncomment the line that has been commented out (if _bit == 0 then end).
It does NOT segfault if I do not require luarocks.loader.
Does anybody have an idea of why this happens or how I could help debug
it? Can anybody reproduce it?
Thanks for your help,
--
Pierre 'catwell' Chapuis