RE: MIPS deadlock bug fix

[Slegers, Walter]

Hi Godmar,

> Are you saying that there's no access to any atomic instruction
> (test-and-set, cmp-exchange, fetch-and-add, whatever) in usermode
> on the MIPS R3000?

It's sad but true.

> Well, then why don't you put the generic version with jthread_ in 
> your config/mips/... file and ifdef it with (R3000) or whatever macro
> the compiler defines when compiling for it.  I take it the R4000 fixes
> that oversight.

Done. My locks.c file is now back to the original version.
I've modified config/mips/common.h to contain:

        #ifndef __mips_common_h
        #define __mips_common_h

        #ifdef __R3000__

        /* only works when Kaffe is compiled with jthreads */

        #define COMPARE_AND_EXCHANGE(A,O,N)             \
        ({                                              \
                int val = 0;                            \
                                                        \
                jthread_suspendall();                   \
                if (*A == O)                            \
                {                                       \
                        *A = N;                         \
                        val = 1;                        \
                }                                       \
                jthread_unsuspendall();                 \
                val;                                    \
        })

        #else

        #define COMPARE_AND_EXCHANGE(A,O,N)             \
        ({                                              \
                unsigned int tmp, ret;                  \
                                                        \
                asm volatile(                           \
                "       .set    noreorder\n"            \
                "       .set    mips2\n"                \
                "       li      %1, 0\n"                \
                "1:     ll      %0, %3\n"               \
                "       bne     %0, %4, 2f\n"           \
                "       move    %0, %5\n"               \
                "       sc      %0, %2\n"               \
                "       beqz    %0, 1b\n"               \
                "       nop\n"                          \
                "       li      %1, 1\n"                \
                "2:     .set    mips0\n"                \
                "       .set    reorder\n"              \
                : "=&r" (tmp), "=r" (ret), "=m" (*(A))  \
                : "m" (*(A)), "r" (O), "r" (N)          \
                : "memory");                            \
                ret;                                    \
        })

        #endif

The non R3000 part is from Edouard. I can only say that it compiles and
I think it works. Edouard can you test it and let us know?
For my R3000 it compiles, and runs repeatedly without problems.

Kind regards,
    Walter



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