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    SubjectRe: [PATCH 20/30] microblaze_mmu_v1: uaccess MMU update
    Date
    On Wednesday 29 April 2009, Michal Simek wrote:
    > > The above is just the nommu variant. For mmu, you need to
    > > have exception handling in __clear_user to take care of the
    > > case where the address is part of the user mapping (access_ok)
    > > but not currently mapped.
    >
    > Is it possible to do it for noMMU kernel too? I mean current MMU
    > implementation of __clear_user in asm is faster than call memset
    > for noMMU. I think I can use MMU implementation for noMMU too.
    > Add two words to __ex_table just extend size of one section but
    > not too much and won't be used for noMMU.

    Well, you can probably do something like this:

    #ifdef CONFIG_MMU
    #define __FIXUP_SECTION ".section .fixup,\"ax\"\n"
    #define __EX_TABLE_SECTION ".section __ex_table,\"a\"\n"
    #else
    #define __FIXUP_SECTION ".section .discard,\"ax\"\n"
    #define __EX_TABLE_SECTION ".section .discard,\"a\"\n"
    #endif

    +#define __get_user_asm(insn, __gu_ptr, __gu_val, __gu_err) \
    +({ \
    + __asm__ __volatile__ ( \
    + "1:" insn " %1, %2, r0; \n" \
    + " addk %0, r0, r0; \n" \
    + "2: \n" \
    + __FIXUP_SECTION \
    + "3: brid 2b \n" \
    + " addik %0, r0, %3 \n" \
    + ".previous \n" \
    + __EX_TABLE_SECTION \
    + ".word 1b,3b \n" \
    + ".previous \n" \
    + : "=r"(__gu_err), "=r"(__gu_val) \
    + : "r"(__gu_ptr), "i"(-EFAULT) \
    + ); \
    +})

    This should simply throw away all the fixups if you list the .discard
    section in vmlinux.lds.S under '/DISCARD/:', so you have no
    overhead at all.

    Arnd <><


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