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Date: Wed, 13 Jun 2007 16:25:07 -0400
From: "Ryan Riley" <rileyrd@gmail.com>
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Subject: [Qemu-devel] CPUTLBEntry Question
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To: qemu-devel@nongnu.org

I'm making some small changes to the TLB stuff in QEMU 0.9.0
(specifically, I'm only working with i386-softmmu) and have run into
an odd question I'm hoping someone can answer for me.  The CPUTLBEntry
structure definition in cpu-defs.h looks like this...

typedef struct CPUTLBEntry {
    /* bit 31 to TARGET_PAGE_BITS : virtual address
       bit TARGET_PAGE_BITS-1..IO_MEM_SHIFT : if non zero, memory io
                                              zone number
       bit 3                      : indicates that the entry is invalid
       bit 2..0                   : zero
    */
    target_ulong addr_read;
    target_ulong addr_write;
    target_ulong addr_code;
    /* addend to virtual address to get physical address */
    target_phys_addr_t addend;
} CPUTLBEntry;

If I change it to add another member, like so..

typedef struct CPUTLBEntry {
    /* bit 31 to TARGET_PAGE_BITS : virtual address
       bit TARGET_PAGE_BITS-1..IO_MEM_SHIFT : if non zero, memory io
                                              zone number
       bit 3                      : indicates that the entry is invalid
       bit 2..0                   : zero
    */
    target_ulong addr_read;
    target_ulong addr_write;
    target_ulong addr_code;
    /* addend to virtual address to get physical address */
    target_phys_addr_t addend;
    /* New member */
    target_phys_addr_t blah;
} CPUTLBEntry;

then QEMU crashes on startup.  (It also crashes if I put that blah
entry on the beginning instead of the end.)  I'm sure there's code
somewhere that must be making assumptions about the size of TLB entry,
but I'm at a loss for finding it.  (I have noticed that the assembly
code in softmmu_header.h indexes to the addend based on addr_read or
addr_write, but adding a new member to the end of the structure
shouldn't impact that, right?)

If anyone has any insight, I would be very appreciative.

Thanks
Ryan