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Index > Compiler Internals > [bug]SWAPGS bug and inconsistent error reporting with 64bit

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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Inconsistent error reporting with new 64bit instructions
Code:

use64

;the following should be valid in 64bit mode

swapgs                  ;<-- error: illegal instruction.

use32

;the following two should not be valid outside 64bit mode

syscall                 ;<-- no error!
sysret                  ;<-- no error!

;the following two should generate "illegal instruction"

cmpxchg16b dqword[0]    ;<-- error: invalid size of operand.
movsxd rax,eax          ;<-- error: invalid size of operand.

;these others are okay

cdqe                    ;<-- error: illegal instruction.
cmpsq                   ;<-- error: illegal instruction.
lodsq                   ;<-- error: illegal instruction.
movsq                   ;<-- error: illegal instruction.
stosq                   ;<-- error: illegal instruction.    
Post 20 Apr 2006, 09:39
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Hmm, Intel and AMD cannot agree on the syscall/sysenter/sysexit/sysret validity.

Intel says syscall/sysret are only valid in 64bit modes
Amd says syscall/sysret are valid in all modes

Intel says sysenter/sysexit are valid in all modes
Amd says sysenter/sysexit are only valid in 32bit modes
Post 20 Apr 2006, 11:13
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Tomasz Grysztar
Assembly Artist


Joined: 16 Jun 2003
Posts: 7724
Location: Kraków, Poland
Tomasz Grysztar
Fixed what had to be fixed.
Post 20 Apr 2006, 20:18
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Thanks for the fixes, much appreciated. Especially swapgs, I was using "db 15,1,0f8h" to get around the problem.

Do you think it is a good idea to make swapgs invalid in 32 bit code?
Post 24 Apr 2006, 12:14
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