Re: [Qemu-devel] [PATCH for-2.12] tcg/mips: Handle large offsets from target env to tlb_table

["Alex Bennée" <alex.bennee@linaro.org>]

Peter Maydell <peter.maydell@linaro.org> writes:

> The MIPS TCG target makes the assumption that the offset from the
> target env pointer to the tlb_table is less than about 64K. This
> used to be true, but gradual addition of features to the Arm
> target means that it's no longer true there. This results in
> the build-time assertion failing:
>
> In file included from /home/pm215/qemu/include/qemu/osdep.h:36:0,
>                  from /home/pm215/qemu/tcg/tcg.c:28:
> /home/pm215/qemu/tcg/mips/tcg-target.inc.c: In function ‘tcg_out_tlb_load’:
> /home/pm215/qemu/include/qemu/compiler.h:90:36: error: static assertion failed: "not expecting: offsetof(CPUArchState, tlb_table[NB_MMU_MODES - 1][1]) > 0x7ff0 + 0x7fff"
>  #define QEMU_BUILD_BUG_MSG(x, msg) _Static_assert(!(x), msg)
>                                     ^
> /home/pm215/qemu/include/qemu/compiler.h:98:30: note: in expansion of macro ‘QEMU_BUILD_BUG_MSG’
>  #define QEMU_BUILD_BUG_ON(x) QEMU_BUILD_BUG_MSG(x, "not expecting: " #x)
>                               ^
> /home/pm215/qemu/tcg/mips/tcg-target.inc.c:1236:9: note: in expansion of macro ‘QEMU_BUILD_BUG_ON’
>          QEMU_BUILD_BUG_ON(offsetof(CPUArchState,
>          ^
> /home/pm215/qemu/rules.mak:66: recipe for target 'tcg/tcg.o' failed
>
> An ideal long term approach would be to rearrange the CPU state
> so that the tlb_table was not so far along it, but this is tricky
> because it would move it from the "not cleared on CPU reset" part
> of the struct to the "cleared on CPU reset" part.

Is that really a problem? Doesn't it mean we'll just reload the TLB
after a reset?

--
Alex Bennée