#5230: Segfault in cgrun064
----------------------------------+-----------------------------------------
Reporter: daniel.is.fischer | Owner: tibbe
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: x86 | Failure: None/Unknown
----------------------------------+-----------------------------------------
Changes (by tibbe):
* os: Linux => Unknown/Multiple
Comment:
I've stared at the assembly for `GHC.PrimopWrappers.copyArray#` (as
reported by GDB's disassemble command) but I can't figure out what's going
on. Here's the (partially annotated) assembly:
{{{
ghczmprim_GHCziPrimopWrappers_copyArrayzh_info:
mov 0x0(%ebp),%eax ; eax = src
mov 0x4(%ebp),%ecx ; ecx = src_off
mov 0x8(%ebp),%edx ; edx = dst
mov %eax,0x40(%esp) ; save src on the stack
mov 0xc(%ebp),%eax ; eax = dst_off
mov %eax,0x4c(%esp) ; save dst_off on the stack
mov 0x10(%ebp),%eax ; eax = n
mov %eax,0x58(%esp) ; save n on the stack
mov 0x2430e0,%eax ; set header
mov %eax,(%edx) ; set header cont.
sub $0x4,%esp
mov 0x5c(%esp),%eax ; eax = n
shl $0x2,%eax ; eax = BYTES(n)
push %eax ; 3rd memcpy arg = BYTES(n)
shl $0x2,%ecx ; ecx = BYTES(src_off)
mov 0x48(%esp),%eax ; eax = src
add $0xc,%eax ; eax = src + 12
add %ecx,%eax ; eax = src + 12 + BYTES(src_off)
push %eax ; 2nd memcpy arg = src + 12 +
BYTES(src_off)
mov 0x58(%esp),%eax ; eax = dst_off
mov %eax,%ecx ; ecx = dst_off
shl $0x2,%ecx ; ecx = BYTES(dst_off)
lea 0xc(%edx),%eax ; eax = dst + 12
add %ecx,%eax ; eax = dst + 12 + BYTES(dst_off)
push %eax ; 1st memcpy arg = dst + 12 +
BYTES(dst_off)
mov %edx,0x74(%esp) ; save edx
call 0x2426da <dyld_stub_memcpy> ; caller-saves: eax, ecx, edx
add $0x10,%esp ; stack clean-up
mov 0x4c(%esp),%eax ; eax = n
mov %eax,%ecx ; ecx = n
shr $0x7,%ecx ; ecx = n >> 7
sub $0x7,%esp ; ??? Why subtract 7?
mov $0x1,%edx ; edx = 1
sub %ecx,%edx ; edx = 1 - (n >> 7)
mov %ecx,0x74(%esp) ; save edx
mov 0x5c(%esp),%ecx
add %ecx,%eax
shr $0x7,%eax
add %edx,%eax
push %eax
push $0x1
mov 0x70(%esp),%eax
mov 0x4(%eax),%ecx ; crash here
shl $0x2,%ecx
mov 0x7c(%esp),%edx
add %edx,%ecx
add $0xc,%eax
add %ecx,%eax
push %eax
call 0x2426e6 <dyld_stub_memset>
add $0x10,%esp
add $0x14,%ebp
jmp *0x0(%ebp)
sbb %al,(%eax)
add %al,(%eax)
xchg %ax,%ax
}}}
I recommend reading it side-by-side with `emitCopyArray` from
`compiler/codeGen/CgPrimOp.hs`.
The assembly makes sense to me up to the point where 7 is subtracted from
the stack pointer.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5230#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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