[Qemu-devel] CPUTLBEntry Question

[Ryan Riley]

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