What is the issue when attempting to read from a memory address using ptrace(PTRACE_PEEKDATA)?

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There could be several issues when attempting to read from a memory address using ptrace(PTRACE_PEEKDATA):

1. The specified memory address might not be accessible to the calling process due to permission restrictions or the memory being protected by a memory management unit (MMU).

2. The memory address might not contain valid data, such as uninitialized memory or memory that has been freed.

3. The process being traced might have terminated, causing the memory address to become invalid or inaccessible.

4. There could be a problem with the ptrace system call itself, such as a failure to attach to the target process or a communication error between the tracer process and the traced process.