flat assembler
Message board for the users of flat assembler.

Index > Main > Silly or BUG: INC [EBX] vs INC [EBP] ???

Author
Thread Post new topic Reply to topic
DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Code:
INC DWORD [EBX]
    


2 Byte's

Code:
INC DWORD [EBP]
    


3 Byte's

No way to encode [EBP] with just 2 Byte's ???
Post 12 Jun 2010, 23:20
View user's profile Send private message Reply with quote
LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
DOS386 wrote:
Code:
INC DWORD [EBX]
    


2 Byte's

Code:
INC DWORD [EBP]
    


3 Byte's

No way to encode [EBP] with just 2 Byte's ???
Refer to "Table 2-2. 32-Bit Addressing Forms with the ModR/M Byte" in Intel's manual vol2A. As you'll see, "INC DWORD [EBP+$00]" is the shortest.
Post 12 Jun 2010, 23:56
View user's profile Send private message Reply with quote
score_under



Joined: 27 Aug 2009
Posts: 27
score_under
MOV EAX,[ESP+4] = 4 bytes.
MOV EAX,[EBP+4] = 3 bytes.

It's just one of those cases where there actually *is* a difference between registers on x86 Wink
Post 14 Jun 2010, 19:55
View user's profile Send private message Reply with quote
bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
Also note: DOS386's code assumes use32
Post 14 Jun 2010, 23:50
View user's profile Send private message Reply with quote
score_under



Joined: 27 Aug 2009
Posts: 27
score_under
bitshifter wrote:
Also note: DOS386's code assumes use32

Uhh... real men use64 or something? Razz
Post 20 Jun 2010, 19:37
View user's profile Send private message Reply with quote
baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
score_under,

16/64-bit inc [ebx] requires address-size prefix and can't be 2 bytes long. 32-bit can.
Post 20 Jun 2010, 20:57
View user's profile Send private message Reply with quote
DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Thanks.

> assumes use32

Right.
Post 27 Jun 2010, 11:00
View user's profile Send private message Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2020, Tomasz Grysztar. Also on GitHub, YouTube, Twitter.

Website powered by rwasa.