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Index > Compiler Internals > [fixed in 1.69.11 BUG] CALL AX vs CALL EAX

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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Code:
 
call ax 
call eax 
    


Both instructions compile happily into very same code Confused

EDIT : fixed status


Last edited by DOS386 on 20 Dec 2009, 07:48; edited 1 time in total
Post 18 Dec 2009, 02:03
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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revolution
DOS386 wrote:
Both instructions compile happily into very same code Confused
True in 16bit mode.

In 32bit mode the prefix is properly added.
Post 18 Dec 2009, 02:08
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sinsi



Joined: 10 Aug 2007
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sinsi
EAX in 16-bit mode would need to be FFFF or less wouldn't it? So 'call eax' is really only 'call ax' anyway.
Post 18 Dec 2009, 02:17
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revolution
When all else fails, read the source


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revolution
sinsi wrote:
EAX in 16-bit mode would need to be FFFF or less wouldn't it? So 'call eax' is really only 'call ax' anyway.
No. The programmer might need a fault to be generated. Or the descriptors might not be set to default.
Post 18 Dec 2009, 04:00
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sinsi



Joined: 10 Aug 2007
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sinsi
>The programmer might need a fault to be generated.
OK, I can sort of see that.

>Or the descriptors might not be set to default.
But the code descriptor affects CS and IP in 16-bit, two registers you can't change directly even in 'unreal' mode. EAX into IP doesn't work.
Post 18 Dec 2009, 04:49
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17248
Location: In your JS exploiting you and your system
revolution
sinsi wrote:
But the code descriptor affects CS and IP in 16-bit, two registers you can't change directly even in 'unreal' mode. EAX into IP doesn't work.
Yes, you are right. This is something I always seem to get confused with. Thanks for the correction.
Post 18 Dec 2009, 04:55
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
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Tomasz Grysztar
Fixed in 1.69.11.
Post 19 Dec 2009, 18:50
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
Tomasz Grysztar wrote:
Fixed in 1.69.11.


Great Smile

- Fixed "CALL-EAX-BUG" (in X86_X64.INC Shocked)
- Fixed "PMOVMSKB-64-Bit-BUG"
- Fixed "GPF-beer-BUG" in the DOS IDE Smile

I haven't tested yet, just checked the source Neutral

The docs are same, could you please fix the (minor) docs bugs with the next release ?
Post 20 Dec 2009, 07:46
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