Why is constant data declared in the .code section?

[Sergiu FUNIERU]

I'm talking about this:
\masm32\examples\exampl01\minimum

Why using:

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.code
start:
  jmp mylabel
     szDlgTitle db "Minimum MASM",0
     szMsg      db "  --- Assembler Pure and Simple ---  ",0
   mylabel:

   invoke MessageBox, 0, ADDR szMsg, ADDR szDlgTitle, MB_OK
   invoke ExitProcess, 0
end start

instead of:

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.data
szDlgTitle db "Minimum MASM", 0
szMsg      db "  --- Assembler Pure and Simple ---  ",0

.code
start:
invoke MessageBox, 0, ADDR szMsg, ADDR szDlgTitle, MB_OK
  invoke ExitProcess, 0
end start

In my opinion, the second version looks cleaner. What's the advantage of using jmp over the constant data instead of moving the constant data in the .data segment?

This might look like a trivial question, but, as many people suggested me on this forum, I need to form a style from the very beginning. I am tempted to think there are some reasons I don't understand now for people writing code that looks unnecessary complicated to me.

[hutch--]

Sergiu,

It was a trick long ago to write data in the code section so you did not add a data section, it used to save you 512 bytes. In a serious app you put data in the .DATA section and with UNICODE you can put string data in the resource section in a string table.

[lingo]

"In my opinion, the second version looks cleaner"
You can avoid jmp mylabel1 too...

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.code
szDlgTitle     db "Minimum MASM",0
szMsg         db "  --- Assembler Pure and Simple ---  ",0
start:
invoke MessageBox, 0, ADDR szMsg, ADDR szDlgTitle, MB_OK
invoke ExitProcess, 0
end start

[jj2007]

Adding to Lingo's example:

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include \masm32\include\masm32rt.inc

.code
AppName db "Masm32:", 0
HelloW db "Hello World", 0
SayWow db "A box, wow", 0
SayHi db "Hi", 0

ZeBox: MsgBox 0, offset SayWow, offset SayHi, MB_OK

start: MsgBox 0, offset HelloW, offset AppName, MB_OK
exit

end start ; use this one to see only the code after start:
; end ZeBox ; use this one to see the code after ZeBox:



The assembler starts executing at the label that matches end xxx. We routinely use start: here in the forum, but ZeBox or Main or main work, too. If you have only a few initialised data, you can use the space between .code and start: to insert them without creating an extra .data section. It saves a few bytes: with linker option /MERGE:.rdata=.text it assembles at 1024 bytes.

[dedndave]

the .CONST and .CODE segments are write-protected
any attempt to write to those areas will generate an access privilege exception
(this can be altered by using the VirtualProtect API function)

data is generally placed in one of these segments to prevent "accidental" modification

each segment added to the PE EXE adds 512 bytes to the size of the file
so, instead of creating a new .CONST segment, placing protected data in the .CODE segement saves 512 bytes

if you wanted to, you could place all the initialized data in the .CODE segment
then, during program initialization, use VirtualProtect to enable read-write access to the desired area

[qWord]

if you wanted to, you could place all the initialized data in the .CODE segment
then, during program initialization, use VirtualProtect to enable read-write access to the desired area

alternatively you can declare the code segement as writeable at top of file (before .model):

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_TEXT SEGMENT WRITE EXECUTE
_TEXT ENDS

[dedndave]

good one qWord
i didn't know the right way to do that   :P
i have just modified the PE header - lol

[qWord]

there is one flaw on using SEGMENT: an second empty code segment is generated (the linker also warn about that). This cause the EXE to grow about the size of PE's section alignment, which is mostly 512 Bytes.

[BlackVortex]

Like jj said, polink's merge is the best option in such case.

[qWord]

Like jj said, polink's merge is the best option in such case.

My notic was about making code section writable, not about section combining :bg

BTW: this can also be done with linker: '/SECTION:.text,EW'

[GregL]

512 bytes?  Who cares?  Do it the right way and put constant data in a .CONST segment.

[MichaelW]

512 bytes?  Who cares?  Do it the right way and put constant data in a .CONST segment.

I agree, 512 bytes is effectively nothing.

[jj2007]

Like jj said, polink's merge is the best option in such case.

/MERGE:.rdata=.text works wth MS link.exe, too - 1024 bytes. The practical value is limited, of course, but sometimes it's cute to take symbolic action against the bloat ;-)

[BlackVortex]

Screw practicality, I'm using xor eax,eax \ inc eax  instead of mov eax,1  !!!

[dedndave]

it would be much more fun to use AND EAX,1
that way, you get a random bug   :bg
sometimes it is 1
sometimes it is 0
we can call it "maybe logic"
maybe it is - eh - maybe it isn't