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[Qemu-discuss] Some questions about memory access------target_mmap()&how

From: qi Lee
Subject: [Qemu-discuss] Some questions about memory access------target_mmap()&how can write one byte into memory
Date: Thu, 20 Dec 2012 23:54:22 +0800

Hi all
    If I already have an emulator, all instructions have been carried out. In order to reuse these codes on the other simulation platforms, as Simics, QEMU, SystemC. So, I want to  
skip over QEMU's TCG(guest binary-->IR-->host binary). Just let QEMU controll the cpu's execution and the cpu access QEMU's memory system. Just Load-elf, fetch and load/store operations need to access memory.  QEMU uses target_mmap() to allocate the memory and map the ELF into the memory. But my ELF is very special:
  type              offset               vaddr                 filesize
 PT_LOAD   0x0002f4         0x88000000          0x0016a
 PT_LOAD   0x00045e        0x88000180         0x00006
 PT_LOAD   0x000468        0x88000200         0x00006
ps =  0x88000000 & ~(unsigned long)((1 << 12)-1)) =  0x88000000
po =  0x88000000 &  ((1 << 12)-1) = 0   offset - po is not zero, so the offset is not multiple of the page size, program error. How can this ELF map into the virtual page?
    After allocating and loading the elf, target-arm uses ldl_code() to fetch the instruction from the corresponding memory address. My instruction is very long, it has 128 bytes. 
How can QEMU write one byte into the memory?  I have tried the stub_raw(), but it has the error message: segmentation fault.Are there other methods that allocate the memory space and writes (or read) one bytes into the memory.  Thank you!

best wishes!

Tim Lee(liqijun)

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