Ok, looking at 4030, which is this simple program:
main = do tid <- block $ forkIO $ let x = x in x
killThread tid
It segfaults in stg_BLACKHOLE_info when attempting to
dereference... something (I haven't quite figured out
what yet; what's usually stored in 0x4(%esi) on 32-bit x86
when entering _info blocks?)
0x822a6e0 <stg_CAF_BLACKHOLE_info>: jmp 0x822a620 <stg_BLACKHOLE_info>
0x822a620 <stg_BLACKHOLE_info>: mov 0x4(%esi),%eax
0x822a623 <stg_BLACKHOLE_info+3>: test $0x3,%eax
0x822a628 <stg_BLACKHOLE_info+8>: jne 0x822a663
<stg_BLACKHOLE_info+67>
0x822a62a <stg_BLACKHOLE_info+10>: mov (%eax),%ecx -- SEGFAULT!
Registers right at the segfault:
eax 0x0 0
ecx 0x28 40
edx 0xb7a7e008 -1213734904
ebx 0x8289acc 136878796
esp 0xbfffcd98 0xbfffcd98
ebp 0xb7a808f8 0xb7a808f8
esi 0xb7a7f108 -1213730552
edi 0xb7a7f10c -1213730548
eip 0x822a62a 0x822a62a <stg_BLACKHOLE_info+10>
I believe this is because the code generator didn't write
out the value to the heap, as seen comparing the correct and incorrect
C-- (irrelevant stack/heap overflow checks elided):
Correct:
Hp = Hp + 8;
if (Hp > I32[BaseReg + 92]) goto coY;
I32[Hp - 4] = stg_CAF_BLACKHOLE_info;
I32[Hp + 0] = I32[BaseReg + 96];
foreign "ccall"
newCAF((BaseReg, PtrHint), (R1, PtrHint))[_unsafe_call_];
I32[R1 + 4] = Hp - 4;
I32[R1] = stg_IND_STATIC_info;
I32[Sp - 8] = stg_bh_upd_frame_info;
I32[Sp - 4] = Hp - 4;
Incorrect:
_r7::I32 = R1;
Sp = Sp + 4;
Hp = Hp + 8;
// outOfLine should follow:
// allocDynClosure
I32[Hp - 4] = stg_CAF_BLACKHOLE_info;
_cpa::I32 = Hp - 4;
// XXX: I32[Hp + 0] is never written!!
I32[Sp - 16] = _cpa::I32;
foreign "ccall"
newCAF((BaseReg, PtrHint), (R1, PtrHint))[_unsafe_call_];
_cpa::I32 = I32[Sp - 16];
I32[R1 + 4] = _cpa::I32;
I32[R1] = stg_IND_STATIC_info;
_cpa::I32 = I32[Sp - 16]; // Hp - 4
I32[Sp - 8] = _cpa::I32;
I32[Sp - 12] = stg_upd_frame_info;
It's not clear to me where in the code generator to look to fix this though.
Any pointers?
Cheers,
Edward
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