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shapr / sandsieve

webapp for uploading and collating output of https://github.com/xoreaxeaxeax/sandsifter
BSD 3-Clause "New" or "Revised" License
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Undefined opcodes #1

Open mahmoodn opened 5 years ago

mahmoodn commented 5 years ago

Chris, Regarding your method to find undocumented instructions, I would like to know how did you catch undefined opcodes? I have written a single line of assembly code in C which is __asm__(".byte 0x00"); . GDB then shows 

   0x00000000004004ed <+0>:     55      push   %rbp
   0x00000000004004ee <+1>:     48 89 e5        mov    %rsp,%rbp
   0x00000000004004f1 <+4>:     00 5d c3        add    %bl,-0x3d(%rbp)

As you can see the compiler combines 00 with other things and create an instruction. Therefore, I get segmentation fault.

shapr commented 5 years ago

Hey Mahmood, I think you found a nearby repository, but not the one you wanted.

I think you wanted this one: https://github.com/xoreaxeaxeax/sandsifter

And the info you requested is in https://github.com/xoreaxeaxeax/sandsifter/blob/master/references/domas_breaking_the_x86_isa_wp.pdf