[Qemu-devel] Catching system calls and PIDs in Qemu

[Ricardo Alves <rdq.alves@gmail.com>]

Need Help!

I am editing the Qemu source code to be able to catch every system call made by the guest OS and which processes do those system calls.

I catch the system calls in the "void do_interrupt(CPUState *env1)" (op_helper.c) function by accessing the exception index on the cpu environment (env->exception_index == 0x80) and inspecting the system call ID in the eax register.

The difficulty resides in finding the process that made the system call. Linux uses the thread_info struct to store process information. The method to find this struct location is to apply a mask to the esp register and I would get the struct pointer. In qemu I would just do this -- target_ulong pos = env->regs[R_ESP] & 0xFFFFE000.

The problem is that I don't know how to access the guest main memory. The qemu function I found to access memory was this one -- void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,int len, int is_write) (exec.c). But as far as I know (I could be wrong) this function receives a guest physical adress and the one I have is a guest virtual adress. Can anybody help me convert this guest virtual adress to a guest physical adress?

Thank you.