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Asked: 2026-05-26T15:07:40+00:00

For some reason, I need to translate the virtual address of the code section

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For some reason, I need to translate the virtual address of the code section to physical address. I did following experiment:

  1. I get the virtual address from the start_code and end_code in mm_struct of process A, which are the initial address and final address of the executable code.

  2. I get the CR3 of process A.

  3. I translate the virtual address to physical address page by page. For example, there are 10 pages for code section in process A. I will translate 10 virtual address of each beginning of the page.

  4. I found out some pages will get Page Table Entry(PTE) == 0.Some pages could successfully translate to a physical address.

  5. I tried Firefox and Minicom as my Process, and both of them will get into situation.

I guess my question is: could anyone explain to me why PTE == 0? Does it mean these pages have been swap out to disk? If this is the case, how can I find these pages?

Thanks for any input!!

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1 Answer

  1. Editorial Team

    It looks as if you are trying to perform page table introspection without using the kernel APIs for it. Note that the address space is arranged in a red-black tree of vm_area_struct structs and you should probably use the APIs that traverse them. The mappings might change at any time so using the proper locking for these data structures is necessary.

    For example, see the get_user_pages() function. It can be used to swap-in and temporarily pin the pages into memory. Using this function for page table introspection is usually asked for because once have the physical address in hand then the kernel can swap out the page at any time.

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