Re: [DynInst_API:] InstructionAPI segfault on archive files

[Bill Williams <bill@xxxxxxxxxxx>]

On 07/05/2015 02:22 PM, Alin Mîndroc wrote:
> Hi everyone,
>
> I am using DyninstAPI for a project involving disassembling files, and
> it worked perfectly until I had to use it on archive files (static
> libraries .a).
>
> When I try to get the assembly code for librt.a, a segfault is raised
> inside the "ia32_decode_prefixes" method. The strange thing is that it
> fails for a "call" instruction (hex code e8 00 00 00 00), which was
> already parsed successfully before in another function.
>
> Currently, my way of getting assembly code for a function is to
> instantiate a decoder:
> decoder(currentFunction->isrc()->getPtrToInstruction(crtaddr),
> InstructionDecoder::maxInstructionLength,
> currentFunction->isrc()->getArch());
> Where crtaddr is (last instruction address) + (last instruction size)
> Then, the segfault is thrown for the "call" instruction when I call the
> decode() method on this InstructionDecoder instance.
>
> Any hints on this? Is there any other way of getting assembly code for
> an archive file?
I'd valgrind this. It sounds to me like either your decode buffer has 
gone away somehow or you've overrun it; max instruction length could in 
fact hit a buffer overrun at the end of a mapped-in file.
If you're just doing a linear scan disassemble, you can create a decoder 
with the full size of the buffer and iteratively decode; that's a safer 
approach (assuming that your problem is in fact a buffer overrun).
> Thanks,
> Alin
>
>
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--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx