[M3devel] what does it mean to read a UINT8?
jay.krell at cornell.edu
Sun Sep 22 19:47:07 CEST 2013
UINT8 is [0..255] I think.
I tried "BITS 8 FOR" on it at some point but such things on that family of types (UINT16, UINT32, UINT64) caused compilation errors. (These are all via Ctypes.i3)
The pointer before subtraction is 64K-aligned.
I don't think the other types should matter.
I still have to compare with integrated backend or cm3cg.
> Date: Sun, 22 Sep 2013 12:17:18 -0500
> From: rodney_bates at lcwb.coop
> To: m3devel at elegosoft.com
> Subject: Re: [M3devel] what does it mean to read a UINT8?
> As in my other response, I think you are left entirely too much
> out in the wind by the language/compiler as to what your expectations
> should be. In this particular example, it would help to know the type
> UINT8, and those of 'used', 'info', 'RegionSize', and maybe 'b'. I
> could make some guesses, but that could turn out a snipe hunt.
> Do you mean it copies a full INTEGER into b, or just fetches
> an INTEGER, then extracts from it? What is the alignment of
> the actual address in the failing case?
> On 09/21/2013 10:58 PM, Jay K wrote:
> > It appears that this code:
> > b := LOOPHOLE(used + info.RegionSize - 1, UNTRACED REF UINT8)^;
> > generates a read of a full INTEGER, in this case 8 bytes.
> > Now, I know, I could change it to:
> > b := LOOPHOLE(used + info.RegionSize - BYTESIZE(INTEGER), UNTRACED REF INTEGER)^;
> > What were my expectations wrong in the first place?
> > This code was part of getting stack bounds and it'd read
> > the end of the stack to try to ensure it was correct.
> > I removed it.
> > 0:000> g
> > (15bc.116c): Access violation - code c0000005 (first chance)
> > First chance exceptions are reported before any exception handling.
> > This exception may be expected and handled.
> > *** WARNING: Unable to verify checksum for cm3.exe
> > cm3!ThreadWin32__GetStackBounds+0x1e8:
> > 00000001`3fdf1a78 488b48ff mov rcx,qword ptr [rax-1] ds:00000000`0028
> > ffff=????????????????
> > 0:000> r rax
> > rax=0000000000290000
> > 0:000> r rsp
> > rsp=000000000028fb60
> > 0:000> dv
> > start_L_275 = 0x00000000`00338de0
> > end_L_276 = 0x00000000`00338de8
> > L_501_L_502 = 0n48
> > used_L_272 = 0x00000000`0028f000
> > available_L_273 = 0x00000000`00190000 "--- memory read error at address 0x000000
> > 00`00190000 ---"
> > b_L_274 = 0x30 '0'
> > a_L_271 = 0n48
> > info_L_270 = struct TA669C7A1
> > _frame = struct ThreadWin32__GetStackBounds_Frame_t
> > 0:000> ?? info_L_270
> > struct TA669C7A1
> > +0x000 BaseAddress : 0x00000000`0028f000 "0???"
> > +0x008 AllocationBase : 0x00000000`00190000 "--- memory read error at addr
> > ess 0x00000000`00190000 ---"
> > +0x010 AllocationProtect : 4
> > +0x014 L_7 :  ""
> > +0x018 RegionSize : 0n4096
> > +0x020 State : 0x1000
> > +0x024 Protect : 4
> > +0x028 Type : 0x20000
> > +0x02c L_8 :  ""
> > 0:000> q
> > quit:
> > - Jay
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