Feature Request: Provide an offset for disassembly

[markcox]

When performing a disassembly if the start bytes are not code then the disassembly fails. Could you please add an option to either provide an offset to disassemble from or a way for the disassembly to ignore errors so any headers are skipped over.

[prb28]

This is for memory disassembly or file ?

[grahambates]

If you're disassembling from a symbol address you can apply an offset by writing it as an expression e.g. init+8 to disassemble starting from 8 bytes after the init label:

Hopefully this handles your use case.

@prb28 the help text could do with updating to document that expressions are supported. Also the ${symbol} syntax is still supported but not necessary. You can just use symbol. I'm happy to create a PR for this.

As far as having the disassembler ignore errors, we're really limited by Capstone, which does appear to just give up when it reaches invalid instructions.

[prb28]

@grahambates yes, I've missed that syntax change you've added. If you want you can add a pr of course, but I can do it too.

Capstone is a limitation here. I don't know if there is a better pure JavaScript choice.
At the time emoon, told me that it was the best disassembler (he did part of the m68k code) and it was a tricky game to reimplement it.

[grahambates]

Yeah I agree that writing a new disassembler in JS is not realistic and Capstone is the best option, especially now that WASM means we don't have a dependency on the native binary. I'm also not sure that Capstone's behaviour is necessarily wrong in this case.

[markcox]

Thanks for your comments. This is for disassembling a file.
I found a way to do the disassembly using capstone via radare2.
These are the commands I used to disassemble a boot block ...
I can set the start of the disassembly to 0xc using the 's' command and disassemble using the 'pd' commands.

$ radare2  -am68k decrypted_loader.bin
[0x00000000]> s 0xc
[0x0000000c]> pd
        ┌─< 0x0000000c      601a           bra.b 0x28
        │   0x0000000e      1902           move.b d2, -(a4)
        │   0x00000010      0100           btst.l d0, d0
        │   0x00000012      00e0           invalid
...
[0x0000000c]> s 0x28
[0x00000028]> pdR 5
            0x00000028      49f900dff000   lea.l 0xdff000.l, a4
            0x0000002e      397c7fff009a   move.w 0x7fff, 0x9a(a4)
            0x00000034      397c7fff0096   move.w 0x7fff, 0x96(a4)
            0x0000003a      41ec0180       lea.l 0x180(a4), a0
            0x0000003e      700f           moveq 0xf, d0

When I try to do the dissassembly in vscode...
I press F1 and choose
"amiga assembly: disassemble file"
I get this message:

[prb28]

Never tried to disassemble a boot block. And didn't know radare2 tool. I'll try it to see if it can be improved.