Filling in struct mips64_watch_regs from a 32 bit process

[Earl Chew <echew@ixiacom.com>]

I notice that a 32 bit process running on a 64 bit kernel is expected to
know that it should fill in mips64_watch_regs --- even though it is running
against a 32 bit ABI.

Is this an oversight, or am I missing something ?

[ That same 32 bit process must fill in mips32_watch_regs when running on
  a 32 bit kernel. ]


In arch/mips/include/asm/ptrace.h:

struct mips32_watch_regs {
        unsigned int watchlo[8];
        ...
};

and

struct mips64_watch_regs {
        unsigned long long watchlo[8];
        ...
};

These are used in a union, but sizeof(mips64_watch_regs.watchlo) will not
match sizeof(mips32_watch_regs.watchlo).



For a 64 bit kernel, the code in arch/mips/kernel/ptrace.c reads:


        /* Check the values. */
        for (i = 0; i < current_cpu_data.watch_reg_use_cnt; i++) {
                __get_user(lt[i], &addr->WATCH_STYLE.watchlo[i]);
#ifdef CONFIG_32BIT
                if (lt[i] & __UA_LIMIT)
                        return -EINVAL;
#else
                if (test_tsk_thread_flag(child, TIF_32BIT_ADDR)) {
                        if (lt[i] & 0xffffffff80000000UL)
                                return -EINVAL;
                } else {
                        if (lt[i] & __UA_LIMIT)
                                return -EINVAL;
                }
#endif


Thus for a 64 bit kernel, WATCH_STYLE is defined to be mips64, and the code
goes on to obtain:

        addr->mips64.watchlo[i]

and to verify it based on TIF_32BIT_ADDR.


In other words, the 32 bit process is expected to fill in mips64_watch_regs
when it is running on a 64 bit kernel, and mips32_watch_regs when it is running
on a 32 bit kernel.



Earl