How to skip instructions by setting PC? PANDA script not working

[TheSilentDawn]

I'm trying to use PANDA to skip over certain instructions in a program, but I'm running into issues.

Here’s the relevant C code:

int check_value = 1;
check_value++;
check_value++;  // <-- I want to start skipping from here
check_value++;  

myowntestfunc();

check_value++;
check_value++; // <-- and jump directly to here

printf("%d\n", check_value);

The goal is to skip one or more check_value++ operations and function call, and resume execution from a later point.

I tried the following PANDA Python script:

panda.enable_precise_pc()

@panda.cb_insn_translate
def insn_translate(cpu, pc):
    return pc == skipped_addr

@panda.cb_insn_exec
def insn_exec(cpu, pc):
    if pc == skipped_addr:
        panda.arch.set_pc(cpu, target_addr)
        # panda.flush_tb()  # enabling/disabling this has no effect
        print(f"[*] skip {hex(pc)} to {hex(target_addr)}")
        return True  
    return False

However, this does not work as expected — the execution flow does not jump to target_addr. Instead, the instructions are executed normally without being skipped.

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My question is:

How can I correctly force a jump in control flow by setting the PC?
Is setting the PC and optionally flushing the translation block (flush_tb) supposed to be enough?
Or is there a more reliable way to skip certain instructions at runtime?

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Environment:

• OS:

• Ubuntu 22.04 LTS with default python 3.10.12

• PANDA version:

• https://github.com/panda-re/panda/releases/download/v1.8.58/pandare_22.04.deb
• https://github.com/panda-re/panda/releases/download/v1.8.58/pandare-1.8.58-py3-none-any.whl

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Thanks in advance!

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