[M3devel] what does it mean to read a UINT8?

[Jay K]

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              : [4]  ""
   +0x018 RegionSize       : 0n4096
   +0x020 State            : 0x1000
   +0x024 Protect          : 4
   +0x028 Type             : 0x20000
   +0x02c L_8              : [4]  ""
0:000> q
quit:


 - Jay
 		 	   		  
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