Disassembling issue

Hi everyone,

I’m trying to have lldb being able to debug my architecture. It does it well after loading my elf. But then I run it, stop it in middle, try to disassemble and at that point it seems that I lost some information about my architecture. lldb tries to disassemble it for x86, which in not possible with my toolchain.

Here is a log of what I am doing:

(lldb) file test
Current executable set to ‘test’ (dpu).
(lldb) dis -s 0x80000000
test`__bootstrap:
test[0x80000000] <+0>: jnz id, 0x80000020
test[0x80000008] <+8>: move r0, 0xff
test[0x80000010] <+16>: release r0, 0x0, nz, 0x80000018
test[0x80000018] <+24>: sub r0, r0, 0x1, pl, 0x80000010
(lldb) r
Process 21312 launched: ‘/home/rjodin/work/dpu_tools/llvm/lldb/test/test’ (dpu)
Process 21312 stopped

  • thread #1, name = ‘DPUthread0’, stop reason = Thread stopped
    frame #0: 0x0000000080000090
    (lldb) dis -s 0x80000000
    error: Unable to find Disassembler plug-in for the ‘x86_64’ architecture.
    (lldb)

Any ideas of what I am missing in my implementation?
Thanks,

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The error is coming from source/Commands/CommandObjectDisassemble.cpp . It’s not able to create the disassembler for your architecture. The call to Disassembler::FindPlugin fails.

My guess is something in the call to MCDisasmInstance::Create in source/Plugins/Disassembler/llvm/DisassemblerLLVMC.cpp is failing. Step through that and make sure everything there is working.

Ted

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Hi Ted,

Thank you for the answer.
I’m not sure I understand you well. It seems to me that my program call “Disassembler::FindPlugin” with the “m_options.arch” set to “x86_64”. But my toolchain does not contain a LLVM supporting x86_64, so it feels normal to me that it is not able to create this disassembler. What is weird is that the first time I’m executing it, it managed to do so.

I also have kind of the same issue with breakpoint. It’s like if I’m missing the debug information after I do the “run” command:

(lldb) file test
Current executable set to ‘test’ (dpu).
(lldb) b main
Breakpoint 1: where = test`main + 24 at test.c:8, address = 0x80000078
(lldb) r
Process 21312 launched: ‘/home/rjodin/work/dpu_tools/llvm/lldb/test/test’ (dpu)
Process 21312 stopped

  • thread #1, name = ‘DPUthread0’, stop reason = Thread finished
    frame #0: 0x00000000800000c0
    (lldb) b main
    Breakpoint 2: no locations (pending).
    WARNING: Unable to resolve breakpoint to any actual locations.

When I’m doing the disassembly, I can manage to disassemble if I add the option with my architecture to the command line, but as you can see below, I also do not have the debug information that I had at the first disassembly:

(lldb) file test
Current executable set to ‘test’ (dpu).
(lldb) dis -s 0x80000000
test`__bootstrap:
test[0x80000000] <+0>: jnz id, 0x80000020
test[0x80000008] <+8>: move r0, 0xff
test[0x80000010] <+16>: release r0, 0x0, nz, 0x80000018
test[0x80000018] <+24>: sub r0, r0, 0x1, pl, 0x80000010
(lldb) r
Process 21312 launched: ‘/home/rjodin/work/dpu_tools/llvm/lldb/test/test’ (dpu)
Process 21312 stopped

  • thread #1, name = ‘DPUthread0’, stop reason = Thread finished
    frame #0: 0x00000000800000a0
    (lldb) dis -s 0x80000000
    error: Unable to find Disassembler plug-in for the ‘x86_64’ architecture.
    (lldb) dis -s 0x80000000 -A dpu
    0x80000000: jnz id, 0x80000020
    0x80000008: move r0, 0xff
    0x80000010: release r0, 0x0, nz, 0x80000018
    0x80000018: sub r0, r0, 0x1, pl, 0x80000010

Any ideas about it?Thanks,
Romaric

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Hi Romaric,

The call to Disassembler::FindPlugin should have arch set to your triple. If m_options.arch is not set on the disassembly command line, it will get it from the target:

if (!m_options.arch.IsValid())

m_options.arch = target->GetArchitecture();

That leads me to wonder if your triple is set correctly after you do the run. What is the output from these commands, when you’re stopped?:

target list

platform status

My guess is you’re connected to a remote gdb-server on a simulator for dpu, and it’s telling lldb that the triple is x86_64.x.x.

If target list says the arch is dpu before the run, and x86_64 after the run, we should look at the RSP log. Before the run, type

log enable -f gdb-remote packets

Attach the file to your next message.

Ted

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Hi Ted,

Indeed, my lldb-server was returning the x86 triple.
I have managed to return the good triple by “hacking” the function “GDBRemoteCommunicationServerCommon::Handle_qHostInfo” to return my “ArchSpec” instead of going through the “HostInfo::GetArchitecture()” function.

I think my problem is more about how I added my architecture into lldb. I will start a new thread about it.

Thank you Ted for the answers, it was very helpful.
Romaric

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