Just a few things...

[alksentrs]

Hello to all!

Just a few questions that have been bothering me for a while now:

• How do you change which register MASM uses for the ADDR statement (it always uses EAX) ?
• What's the syntax to differentiate between relative, absolute and indirect jumps & calls ? (neither the opcodes reference nor the assembler reference tells you the syntax for instructions in enough detail...)

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; This code is NOT valid, but shows the effect of jmp (call has a push EIP in front)
; Note: these are all near jumps

add EIP,xxx   ; relative    (xxx is the displacement relative to the next instruction)
lea EIP,[xxx] ; absolute    (xxx is the memory address to jump to)
mov EIP,[xxx] ; indirect    (xxx is the memory address of the memory address to jump to)


• Where is the proper place where all the downloads (most recent MASM, windows.inc, etc) are located?
• Are there MSVCRT.INC and MSVCRT.LIB files available? I don't seem to have them in my MASM directory.

[hutch--]

MASM32 has MSVCRT support. Conditional jumps are NEAR in win32 with a 32k range and SHORT if you use the form that has signed byte range. Unconditional jumps "JMP" have DWORD range.

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Jxx SHORT label   ; signed BYTE range (128 byte)
Jxx NEAR label    ; signed WORD range (32k)
JMP label         ; DWORD range (4 gig)


[alksentrs]

Fast reply!

What I meant was: there are all these different versions of jump and call instructions, yet there doesn't seem to be a way to specify which to use.
E.g.:

Code Select Expand


jmp [eax]


How do you choose between jumping to the memory address in EAX ("absolute"), and jumping to the memory address stored in the pointer that EAX points to ("absolute indirect")?

I had to copy the libmsvcrt.a file out of my C/C++ compiler's lib folder into the MASM lib folder (and rename it to msvcrt.lib), and manually write an .inc file, because they weren't there.

Is my version of MASM outdated ? ... after typing ML at the command line it came up with v. 6.14.8444 ... so that's probably a yes...

[Randall Hyde]

MASM32 has MSVCRT support. Conditional jumps are NEAR in win32 with a 32k range and SHORT if you use the form that has signed byte range. Unconditional jumps "JMP" have DWORD range.

Code Select Expand


Jxx SHORT label   ; signed BYTE range (128 byte)
Jxx NEAR label    ; signed WORD range (32k)
JMP label         ; DWORD range (4 gig)


Actually, NEAR jumps are 32 bits in 32-bit mode (win32).  I used to make that mistake until Frank Kotler caught me on it.
Cheers,
Randy Hyde

[gabor]

Hello!


I quickly created a small test for the absolute and absolute indirect calls/jumps. Here is what I've got:

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     dumyPTR  dd offset dumy
...
     dumy     PROC
              ret
     dumy     ENDP
...
     mov      eax,offset dumy
     call     DWORD PTR eax     ; absolute jump using a register
     call     eax               ;the DWORD PTR can be leaved off

     mov      eax,offset dumyPtr
     call     DWORD PTR [eax]   ; indirect jump using a register
                                ; the size specifier is needed and the square brackets are necessary!


I hope I didn't mess up anything :)
About the size of jumps I didn't really bother so far, I think I use 32bit absolute jump/calls in about 80% of the cases.

Greets, Gábor