wrong opcode?

wrong opcode?

[kieft_brian]

I curious as to why the code generated for these two move.w commands is
completely different. In the first assembly I used two variables (one equal to 0
and the other equal to 8). I tried doing a move using the variables added
together as my offset to register A1 and managed to get 33B9 0000 0000 0170 0000
0008. When I simply put an 8 in instead of the variables, I got the correct
code. 3379 0000 0000 0008. Any ideas??????

I'm using gnu as on a pc-cygwin system with a m68k target. 


3901 034a 0000 0008         .DC.L   C_WCP1_MSG_PARM
 3902 034e 0000 0000        .DC.L   HWPN_PARM_OFS
 3903 0352 33B9 0000 MOVE.W SYS_SYS_VERS_W,C_WCP_MSG_PARM+HWPN_PARM_OFS(%A1)
 3903      0000 0170 
 3903      0000 0008 
  
  
 
 3901 034a 0000 0008        .DC.L   C_WCP1_MSG_PARM
 3902 034e 0000 0000        .DC.L   HWPN_PARM_OFS
 3904                       
 3905 0352 3379 0000        MOVE.W  M_SYS_SYS_VERS_W,8(%A1)
 3905      0000 0008 
 3906      




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Re: wrong opcode?

[Peter Barada]

>I curious as to why the code generated for these two move.w commands
>is completely different. In the first assembly I used two variables
>(one equal to 0 and the other equal to 8). I tried doing a move using
>the variables added together as my offset to register A1 and managed
>to get 33B9 0000 0000 0170 0000 0008. When I simply put an 8 in
>instead of the variables, I got the correct code. 3379 0000 0000
>0008. Any ideas?????? 
>
>I'm using gnu as on a pc-cygwin system with a m68k target. 
>
>
>3901 034a 0000 0008         .DC.L   C_WCP1_MSG_PARM
> 3902 034e 0000 0000        .DC.L   HWPN_PARM_OFS
> 3903 0352 33B9 0000 MOVE.W SYS_SYS_VERS_W,C_WCP_MSG_PARM+HWPN_PARM_OFS(%A1)
> 3903      0000 0170 
> 3903      0000 0008 
>  
>  
> 
> 3901 034a 0000 0008        .DC.L   C_WCP1_MSG_PARM
> 3902 034e 0000 0000        .DC.L   HWPN_PARM_OFS
> 3904                       
> 3905 0352 3379 0000        MOVE.W  M_SYS_SYS_VERS_W,8(%A1)
> 3905      0000 0008 
> 3906      

From what I see, in the case of 0x33b9, its using mode 6 for the
destination which with the extension word of 0x0170 that
decodes(look at page 2-2 of the MC68000 Family Programmer's Reference
Manual) into a full extension word format where:

D/A = 0
REG = 0
W/L = 0
SCALE = 0
BS = 0
IS = 1
BDSIZE = 3
I/IS = 0

Which means that the index register is suppressed, the base register
is not suppressed, the base displacement size is 32 bits, I/S
indicates that no memory indirection is done(so its not pre-indexed or
post-indexed), so this is equivilent to addressing mode 5 but with a
32 bit displacement instead of the 16 bits that mode 5 supports.

I think that this addressing mode is being picked since the assembler
sees the expression C_WCP_MSG_PARM+HWPN_PARM_OFS and determines that
the resulting expression contains 32 bits of significance(including
all possible relocation) and hence can't stuff it into addressing mode 5.

Check how C_WCP_MSG_PARM and HWPN_PARM_OFS are being declared.  is it
with .equ, or is one of them a label(which requires 32 bits of
significance to allow its relocation anywhere in the 4GB address space)?

Hope this helps...

-- 
Peter Barada                                   Peter.Barada@motorola.com
Wizard                                         781-852-2768 (direct)
WaveMark Solutions(wholly owned by Motorola)   781-270-0193 (fax)

Re: wrong opcode?

[Andreas Schwab]

<kieft_brian@si.com> writes:

|> I curious as to why the code generated for these two move.w commands is
|> completely different. In the first assembly I used two variables (one equal to 0
|> and the other equal to 8). I tried doing a move using the variables added
|> together as my offset to register A1 and managed to get 33B9 0000 0000 0170 0000
|> 0008. When I simply put an 8 in instead of the variables, I got the correct
|> code. 3379 0000 0000 0008. Any ideas??????
|> 
|> I'm using gnu as on a pc-cygwin system with a m68k target. 
|> 
|> 
|> 3901 034a 0000 0008         .DC.L   C_WCP1_MSG_PARM
|>  3902 034e 0000 0000        .DC.L   HWPN_PARM_OFS
|>  3903 0352 33B9 0000 MOVE.W SYS_SYS_VERS_W,C_WCP_MSG_PARM+HWPN_PARM_OFS(%A1)
|>  3903      0000 0170 
|>  3903      0000 0008 

The other opcode is not wrong, it just uses the 32bit offset form.  How
are C_WCP_MSG_PARM and HWPN_PARM_OFS defined?  Please provide a complete,
self-contained test case.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."
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