c++ - Wierd behaviour with mixed ASM and C++
- KarL (36/36) Aug 06 2002 charset="iso-8859-1"
- Roland (6/15) Aug 07 2002 you are loading the offset of m_cC in al !
- KarL (80/80) Aug 07 2002 charset="iso-8859-1"
- Jan Knepper (3/5) Aug 07 2002 Are you sure it's not just reserving an 'int' somewhere?
- Walter (23/23) Aug 07 2002 charset="iso-8859-1"
charset="iso-8859-1"
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Source:
class someobj { unsigned char m_cC;public: void =
somebuggyfunction(); void somefunction();}
somepublicfunction(){ __asm mov dx, 0x300 __asm mov al, m_cC =
__asm out dx,al}
void someobj::somebuggyfunction(){ __asm mov dx, 0x300 __asm =
mov al, m_cC __asm out dx,al}
void someobj::somefunction(){ m_cC =3D 0x56;}
Obj2ASM output:
_TEXT segment dword use32 public 'CODE' ;size is 28_TEXT =
ends_DATA segment dword use32 public 'DATA' ;size is 0_DATA =
endsCONST segment dword use32 public 'CONST' ;size is 0CONST =
ends_BSS segment dword use32 public 'BSS' ;size is 0_BSS =
endsFLAT groupincludelib SNN.lib
public ?somepublicfunction YA?AVsomeobj XZ public =
?somebuggyfunction someobj QAEXXZ public =
?somefunction someobj QAEXXZ_TEXT segment assume =
CS:_TEXT?somepublicfunction YA?AVsomeobj XZ: mov =
DX,0300h mov AL,0 out DX,AL =
ret?somebuggyfunction someobj QAEXXZ: enter =
4,0 mov -4[EBP],ECX mov DX,0300h =
mov AL,0 out DX,AL =
leave ret?somefunction someobj QAEXXZ: =
mov byte ptr [ECX],056h ret_TEXT ends_DATA =
segment_DATA endsCONST segmentCONST ends_BSS segment_BSS =
ends end
My Comments:
The "somepublicfunction" did not report the error on using m_cC in the =
inline assembly - since
m_cC is not declared as a global variable.
The same thing with someobj::somepublicfunction which failed to generate =
the someobj::m_cC
reference.
someobj::somefunction appears to be OK.
Aug 06 2002
KarL a écrit :
Source:
.
.
somepublicfunction()
{
__asm mov dx, 0x300
__asm mov al, m_cC
__asm out dx,al
}
you are loading the offset of m_cC in al !
you have to do like this:
asm mov eax,this
asm mov al,[eax].m_cC
roland
Aug 07 2002
charset="iso-8859-1"
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Roland <rv ronetech.com> wrote in message =
news:3D50F00A.EBF0567 ronetech.com...
=20
KarL a =E9crit :=20
Source:=20
.=20
.=20
somepublicfunction()
{
__asm mov dx, 0x300
__asm mov al, m_cC
__asm out dx,al
}
you are loading the offset of m_cC in al !=20
you have to do like this:=20
asm mov eax,this=20
asm mov al,[eax].m_cC=20
roland=20
NO. It shouldn't even compile at all!
somepublicfunction() is a global function and is unable to even see =
m_cC!
Borland's compilers both returns the following messages:
C:\tmp\bugtest>bcc32 -S bug.cppBorland C++ 5.0 for Win32 Copyright (c) =
1993, 1996 Borland Internationalbug.cpp:Error bug.cpp 9: Type 'someobj' =
may not be defined hereWarning bug.cpp 13: Function should return a =
value in function somepublicfunction()Error bug.cpp 18: Expression =
syntax in function someobj::somebuggyfunction()*** 2 errors in Compile =
***
C:\tmp\bugtest>bcc -S bug.cppBorland C++ 5.0 Copyright (c) 1987, 1996 =
Borland Internationalbug.cpp:Error bug.cpp 9: Type 'someobj' may not be =
defined hereWarning bug.cpp 13: Function should return a value in =
function somepublicfunction()Error bug.cpp 18: Expression syntax in =
function someobj::somebuggyfunction()*** 2 errors in Compile ***
What was missed in the defination of the class someobj is at the end of =
the class
defination, there was NO ';' at the end of the '}' after the defination =
of someobj.
What I change it to this:
class someobj { unsigned char m_cC; // This is private to someobj =
onlypublic: void somebuggyfunction(); void somefunction();}; // =
NOTICE THE ';' now...
somepublicfunction() // This is a global function{ __asm mov dx, =
0x300 __asm mov al, m_cC // trying to access non global variable =
__asm out dx,al}
void someobj::somebuggyfunction(){ __asm mov dx, 0x300 __asm =
mov al, m_cC // Question, 16-bit and 32-bit compatible??? __asm =
out dx,al}
void someobj::somefunction(){ m_cC =3D 0x56;}
Borland compilers now says:
C:\tmp\bugtest>bcc -S bug.cppBorland C++ 5.0 Copyright (c) 1987, 1996 =
Borland Internationalbug.cpp:Warning bug.cpp 13: Function should return =
a value in function somepublicfunction()Error bug.cpp 18: Expression =
syntax in function someobj::somebuggyfunction()*** 1 errors in Compile =
***
C:\tmp\bugtest>bcc32 -S bug.cppBorland C++ 5.0 for Win32 Copyright (c) =
1993, 1996 Borland Internationalbug.cpp:Warning bug.cpp 13: Function =
should return a value in function somepublicfunction()Error bug.cpp 18: =
Expression syntax in function someobj::somebuggyfunction()*** 1 errors =
in Compile ***
It now correctly informed me that I can't use that expression for =
accessing the class member m_cC but
also failed to tell me that someglobalfunction cannot see m_cC.
If I change the someglobalfunction()'s accessing of m_cC into something =
else, DM will tell me this:
C:\tmp\bugtest>sc -C bug.cpp __asm mov al, =
ThisIsABogusVariable =
^bug.cpp(11) : Warning 13: Illegal type/size of operands for the mov =
instruction}^bug.cpp(13) : Error: undefined label =
'ThisIsABogusVariable'--- errorlevel 1
This is what should have been expected.
To make both DM and BC compilers happy, and also 16-bit and 32-bit =
source level compatible,
this is the fix:
void someobj::somebuggyfunction(){ unsigned char uc =3D m_cC; // =
Use the stack to get member variable __asm mov dx, 0x300 __asm =
mov al, uc // Now both 16-bit and 32-bit is OK... (I think) =
__asm out dx,al}
Have a nice day Walter. ;-)
Aug 07 2002
Jan Knepper <jan smartsoft.cc> KarL wrote:NO. It shouldn't even compile at all! somepublicfunction() is a global function and is unable to even see m_cC!Are you sure it's not just reserving an 'int' somewhere? Jan
Aug 07 2002
charset="iso-8859-1"
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Lookup rules in inline asm are a little different. All struct members =
are included in the search, regardless of protection attributes, =
scoping, etc. This sounds a little wierd, but is intentional. It's =
fallout from trying to emulate MASM syntax, and MASM has little concept =
of structs, scoping, etc. Secondly, all struct members resolve to simply =
an integer representing the offset of that member from the start of the =
struct. This is so that it can be used as an offset to whatever 'this' =
value is in the index register:
mov EAX, foo[ECX]
I hope this clears up the confusion.
-Walter
"KarL" <someone somewhere.org> wrote in message =
news:aiq0sh$d69$1 digitaldaemon.com...
Source:
The "somepublicfunction" did not report the error on using m_cC in the =
inline assembly - since
m_cC is not declared as a global variable.
The same thing with someobj::somepublicfunction which failed to =
generate the someobj::m_cC
reference.
someobj::somefunction appears to be OK.
Aug 07 2002
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Walter <walter digitalmars.com> wrote in message =
news:aisitv$29es$1 digitaldaemon.com...
Lookup rules in inline asm are a little different. All struct members =
are included in the search, regardless of protection attributes, =
scoping, etc. This sounds a little wierd, but is intentional. It's =
fallout from trying to=20
Heh heh heh, I did say the word "Wierd" in the subject of this post.
emulate MASM syntax, and MASM has little concept of structs, scoping, =
etc. Secondly, all struct members resolve to simply an integer =
representing the offset of that member from the start of the struct. =
This is so that it can be used as an offset to whatever 'this' value is =
in the index register:
=20
mov EAX, foo[ECX]
=20
I hope this clears up the confusion.
=20
-Walter
I did figured it out (see the other post). Basically maintaining =
"source level compatibility"
across compilers and cpu target is never easy the moment inline =
assemblies are used.
Aug 07 2002
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You're right. That is why in the D language, the inline assembler is =
specified.
"KarL" <someone somewhere.org> wrote in message =
news:aisl3m$2bqa$1 digitaldaemon.com...
I did figured it out (see the other post). Basically maintaining =
"source level compatibility"
across compilers and cpu target is never easy the moment inline =
assemblies are used.
Aug 07 2002
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Lastly, if I recompile using Borland compiler:
C:\tmp\bugtest>bcc -c bug.cppBorland C++ 5.0 Copyright (c) 1987, 1996 =
Borland Internationalbug.cpp:Error bug.cpp 11: Undefined symbol 'm_cC' =
in function somepublicfunction()Warning bug.cpp 13: Function should =
return a value in function somepublicfunction()*** 1 errors in Compile =
***
Borland did pick up the error! So this is not only the assembly syntax =
compatibilities.
Walter <walter digitalmars.com> wrote in message =
news:aisitv$29es$1 digitaldaemon.com...
Lookup rules in inline asm are a little different. All struct members =
are included in the search, regardless of protection attributes, =
scoping, etc. This sounds a little wierd, but is intentional. It's =
fallout from trying to emulate MASM syntax, and MASM has little concept =
of structs, scoping, etc. Secondly, all struct members resolve to simply =
an integer representing the offset of that member from the start of the =
struct. This is so that it can be used as an offset to whatever 'this' =
value is in the index register:
=20
mov EAX, foo[ECX]
=20
I hope this clears up the confusion.
=20
-Walter
Aug 07 2002