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Index > Windows > x64 SEH Jump to label from exception handler

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pro3carp3



Joined: 16 Jun 2019
Posts: 2
Location: Iowa
pro3carp3
I'm adding some exception handling using the example here: https://board.flatassembler.net/topic.php?t=11266.

The example transfers control back to the procedure by setting context.Rip to the point immediately past the errant code:

Code:
buggy_instruction:
   div     ebx
sizeof_buggy_instruction =       $ - buggy_instruction
...
add     [context.Rip],sizeof_buggy_instruction 
    


Rather than jump to the code following the error, however, I want to jump to a particular label to handle the exception, similar to a finally block.

I'm getting a value out of range error when attempting this:
Code:
mov [context.Rip], finally_label
    


How do I adjust the context.Rip to jump to the finally label upon exiting the exception handler?

Thanks.
Post 25 May 2022, 04:08
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ProMiNick



Joined: 24 Mar 2012
Posts: 688
Location: Russian Federation, Sochi
ProMiNick
finally_label - is 64 bit immediate value.
only instruction that accept 64 IMM is "mov REG, IMM64" so
mov RAX, finally_label
mov [context.Rip], RAX
will work.
Post 25 May 2022, 05:03
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sinsi



Joined: 10 Aug 2007
Posts: 751
Location: Adelaide
sinsi
Isn't it better for 64-bit code to use LEA rather than MOV? I thought MOV would give a 64-bit address but LEA would use RIP-relative (and no relocation).
Post 25 May 2022, 09:04
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Furs



Joined: 04 Mar 2016
Posts: 1888
Furs
Code:
add [context.Rip], finally_label - buggy_instruction    
Post 25 May 2022, 13:24
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pro3carp3



Joined: 16 Jun 2019
Posts: 2
Location: Iowa
pro3carp3
I should have realized that. Thank you.
Post 26 May 2022, 02:42
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